Copolyesters of ε-caprolactone and l-lactide catalyzed by a tetrabutylammonium phthalimide-N-oxyl organocatalyst

Aliphatic polyesters are biocompatible materials that can be used in biomedical applications. We report here the use of tetrabutylammonium phthalimide-N-oxyl catalyst (TBAPINO), as a thermally stable organocatalyst for the ring-opening polymerization (ROP) of cyclic esters under mild conditions. In the solution ROP of ε-caprolactone (ε-CL), quantitative conversion and M_n of ∼20 000 g mol⁻¹ are achieved in a wide temperature range from −15 to 60 °C. Under bulk condition, the conversion of ε-CL reaches over 85% at 120 °C within 2 h. The living ROP character of l-lactide (l-LA) catalyzed over TBAPINO is proved by multiple additions of monomer in the bulk polymerization. The catalyst shows comparable selectivity towards the ring-opening polymerization of l-LA and ε-CL. Their copolymerization over TBAPINO is carried out in one-pot bulk condition in terms of the reaction time, monomer feed ratio, and sequence of addition. The colorless poly(ε-caprolactone-co-lactide) (PCLA) is obtained with considerable conversion of both monomers with the M_n over 22 000 g mol⁻¹.

By utilizing tetrabutylammonium phthalimide-N-oxyl organocatalyst, copolymer PCLA with M_n over 20 000 g mol⁻¹ was synthesized by sequential ring-opening polymerization of ε-caprolactone and l-lactide under bulk conditions.     

Ethylene-bridged polysilsesquioxane/hollow silica particle hybrid film for thermal insulation material

Ethylene-bridged polysilsesquioxane (EBPSQ) was prepared by the sol–gel reaction of bis(triethoxysilyl)ethane. The whitish slurry was prepared by mixing EBPSQ and hollow silica particles (HSPs) with a median diameter of 18–65 μm at 80 °C, and it formed a hybrid film by heating at 80 and 120 °C for 1 h at each temperature, then at 200 °C for 20 min. The surface temperatures of EBPSQ films containing 10 wt% and 20 wt% of HSPs (90.2 °C–90.5 °C) were lower than those of EBPSQ films (93.6 °C), when the films on the duralumin plate were heated at 100 °C for 10 min from the bottom of the duralumin plate. The thermal conductivity/heat flux (k/q) obtained from the temperature difference between the surface temperature and bottom temperature of the films and the film thickness also decreased with adding the HSPs. EBPSQ film without HSPs exhibited T⁵_d of 258 °C and T¹⁰_d of 275 °C. However, EBPSQ film containing 20 wt% of HSPs exhibited high thermal stability, and T⁵_d and T¹⁰_d were 299 °C and 315 °C, respectively. Interestingly, T⁵_d and T¹⁰_d of the hybrid films increased with an increase in the number of HSPs. Overall, it was shown that HSPs could improve the thermal insulation properties and thermal stability.

Ethylene-bridged polysilsesquioxane/hollow silica particle hybrid films were prepared by the sol–gel reaction. The hybrid film containing hollow silica particles exhibited good thermal insulation properties and thermal stability.     

Phosphorus pentoxide as a cost-effective,metal-free catalyst for ring opening polymerization of ε-caprolactone

The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) using phosphorus pentoxide (P₂O₅) as a metal-free catalyst and isopropanol (iPrOH) as initiator resulted in the preparation of poly(ε-caprolactone) with narrow weight distribution. NMR spectroscopy analyses of the prepared PCL indicated the presence of the initiator residue at the end of the polymer chain, implying the occurrence of the ε-CL-catalysis ROP through a monomer activation mechanism. Kinetic experiments confirmed the controlled/living nature of ε-CL ring-opening catalyzed by phosphorus pentoxide. The commercial availability of phosphorus pentoxide and its easy-handling provide additional opportunities for polymer synthesis and nanocomposite manufacturing.

The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) using phosphorus pentoxide (P₂O₅) as a metal-free catalyst and isopropanol (iPrOH) as initiator resulted in the preparation of poly(ε-caprolactone) with narrow weight distribution.     

Eucalyptus red grandis pretreatment with protic ionic liquids: effect of severity and influence of sub/super-critical CO2 atmosphere on pretreatment performance

Deconstruction of lignocellulosic biomass with low-cost ionic liquids (ILs) has proven to be a promising technology that could be implemented in a biorefinery to obtain renewable materials, fuels and chemicals. This study investigates the pretreatment efficacy of the ionoSolv pretreatment of Eucalyptus red grandis using the low-cost ionic liquid triethylammonium hydrogen sulfate ([N₂₂₂₀][HSO₄]) in the presence of 20 wt% water at 10% solids loading. The temperatures investigated were 120 °C and 150 °C. Also, the influence of performing the pretreatment under sub-critical and supercritical CO₂ was investigated. The IL used is very effective in deconstructing eucalyptus, producing cellulose-rich pulps resulting in enzymatic saccharification yields of 86% for some pretreatment conditions. It has been found that under a CO₂ atmosphere, the ionoSolv process is pressure independent. The good performance of this IL in the pretreatment of eucalyptus is promising for the development of a large-scale ionoSolv pretreatment processes.

Deconstruction of lignocellulosic biomass with low-cost ionic liquids (ILs) has proven to be a promising technology that could be implemented in a biorefinery to obtain renewable materials, fuels and chemicals.     

High voltage,solvent-free solid polymer electrolyte based on a star-comb PDLLA–PEG copolymer for lithium ion batteries

In this work, a novel star-comb copolymer based on poly(d,l-lactide) (PDLLA) macromonomer and poly(ethylene glycol)methyl ether methacrylate (PEGMA) was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries. The six-arm vinyl functionalized PDLLA macromonomer was synthesized by a ring-opening polymerization (ROP) of d,l-lactide and subsequently an acylation of the hydroxy end-groups. A series of free-standing solid polymer electrolyte membranes from different ratios of PDLLA, PEGMA and LiTFSI were prepared through solvent-free free radical polymerization under UV radiation. The chemical structure of the obtained polymers was confirmed by ¹H NMR and FTIR. The as-prepared six-arm star-comb solid polymer electrolytes (PDLLA-SPEs) exhibit good thermal stability with T_d^5%s of ∼270 °C and low T_gs of −48 to −34 °C. The electrochemical characterization shows that the PDLLA-SPEs possess a wide electrochemical window up to 5.1 V with an optimal ionic conductivity of 9.7 × 10⁻⁵ S cm⁻¹ at 60 °C at an EO/Li⁺ ratio of 16 : 1. Furthermore, the all-solid-state LiFePO₄/Li cells display extraordinary cycling and rate performances at 60 °C by curing the PDLLA-SPEs directly on the cathode. These superior properties of the six-arm star-comb PDLLA-SPE make it a promising candidate solid electrolyte for lithium batteries.

In this work, a novel star-comb copolymer based on PDLLA macromonomer and PEGMA was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries.     

Synthesis and thermal stability of ZrO2@SiO2 core–shell submicron particles

ZrO₂@SiO₂ core–shell submicron particles are promising candidates for the development of advanced optical materials. Here, submicron zirconia particles were synthesized using a modified sol–gel method and pre-calcined at 400 °C. Silica shells were grown on these particles (average size: ∼270 nm) with well-defined thicknesses (26 to 61 nm) using a seeded-growth Stöber approach. To study the thermal stability of bare ZrO₂ cores and ZrO₂@SiO₂ core–shell particles they were calcined at 450 to 1200 °C. After heat treatments, the particles were characterized by SEM, TEM, STEM, cross-sectional EDX mapping, and XRD. The non-encapsulated, bare ZrO₂ particles predominantly transitioned to the tetragonal phase after pre-calcination at 400 °C. Increasing the temperature to 600 °C transformed them to monoclinic. Finally, grain coarsening destroyed the spheroidal particle shape after heating to 800 °C. In striking contrast, SiO₂-encapsulation significantly inhibited grain growth and the t → m transition progressed considerably only after heating to 1000 °C, whereupon the particle shape, with a smooth silica shell, remained stable. Particle disintegration was observed after heating to 1200 °C. Thus, ZrO₂@SiO₂ core–shell particles are suited for high-temperature applications up to ∼1000 °C. Different mechanisms are considered to explain the markedly enhanced stability of ZrO₂@SiO₂ core–shell particles.

Silica encapsulation dramatically enhances the thermal stability of zirconia submicron particles by grain growth inhibition and tetragonal phase stabilization.     

Cerium and tin oxides anchored onto reduced graphene oxide for selective catalytic reduction of NO with NH3 at low temperatures

A series of cerium and tin oxides anchored on reduced graphene oxide (CeO₂–SnO_x/rGO) catalysts are synthesized using a hydrothermal method and their catalytic activities are investigated by selective catalytic reduction (SCR) of NO with NH₃ in the temperature range of 120–280 °C. The results indicate that the CeO₂–SnO_x/rGO catalyst shows high SCR activity and high selectivity to N₂ in the temperature range of 120–280 °C. The catalyst with a mass ratio of (Ce + Sn)/GO = 3.9 exhibits NO conversion of about 86% at 160 °C, above 97% NO conversion at temperatures of 200–280 °C and higher than 95% N₂ selectivity at 120–280 °C. In addition, the catalyst presents a certain SO₂ resistance. It is found that the highly dispersed CeO₂ nanoparticles are deposited on the surface of rGO nanosheets, because of the incorporation of Sn⁴⁺ into the lattice of CeO₂. The mesoporous structures of the CeO₂–SnO_x/rGO catalyst provides a large specific surface area and more active sites for facilitating the adsorption of reactant species, leading to high SCR activity. More importantly, the synergistic interaction between cerium and tin oxides is responsible for the excellent SCR activity, which results in a higher ratio of Ce³⁺/(Ce³⁺ + Ce⁴⁺), higher concentrations of surface chemisorbed oxygen and oxygen vacancies, more strong acid sites and stronger acid strength on the surface of the CeSn(3.9)/rGO catalyst.

A series of cerium and tin oxides anchored on graphene oxide (CeO₂–SnO_x/rGO) catalysts are synthesized for selective catalytic reduction of NO with NH₃ in the temperature range of 120–280 °C.     

Selective hydroconversion of coconut oil-derived lauric acid to alcohol and aliphatic alkane over MoOx-modified Ru catalysts under mild conditions

Molybdenum oxide-modified ruthenium on titanium oxide (Ru–(y)MoO_x/TiO₂; y is the loading amount of Mo) catalysts show high activity for the hydroconversion of carboxylic acids to the corresponding alcohols (fatty alcohols) and aliphatic alkanes (biofuels) in 2-propanol/water (4.0/1.0 v/v) solvent in a batch reactor under mild reaction conditions. Among the Ru–(y)MoO_x/TiO₂ catalysts tested, the Ru–(0.026)MoO_x/TiO₂ (Mo loading amount of 0.026 mmol g⁻¹) catalyst shows the highest yield of aliphatic n-alkanes from hydroconversion of coconut oil derived lauric acid and various aliphatic fatty acid C6–C18 precursors at 170–230 °C, 30–40 bar for 7–20 h. Over Ru–(0.026)MoO_x/TiO₂, as the best catalyst, the hydroconversion of lauric acid at lower reaction temperatures (130 ≥ T ≤ 150 °C) produced dodecane-1-ol and dodecyl dodecanoate as the result of further esterification of lauric acid and the corresponding alcohols. An increase in reaction temperature up to 230 °C significantly enhanced the degree of hydrodeoxygenation of lauric acid and produced n-dodecane with maximum yield (up to 80%) at 230 °C, H₂ 40 bar for 7 h. Notably, the reusability of the Ru–(0.026)MoO_x/TiO₂ catalyst is slightly limited by the aggregation of Ru nanoparticles and the collapse of the catalyst structure.

Ru–(y)MoO_x/TiO₂ catalysed the hydroconversion of lauric acid to allow a remarkable yield of n-dodecane (up to 80%) under mild reaction conditions.     

Binary catalytic system for homo- and block copolymerization of ε-caprolactone with δ-valerolactone

The combined interaction of 2,3,6,7-tetrahydro-5H-thiazolo[3,2-a] pyrimidine (ITU) as the organocatalytic nucleophile with YCl₃ as Lewis acid cocatalyst, generating ITU/YCl₃, was employed for homo- and copolymerization of ε-caprolactone (CL) with δ-valerolactone (VL). Poly(caprolactone) (PCL) and poly(caprolactone)–poly(ethylene glycol)–poly(caprolactone) (PCL–PEG–PCL) triblock copolymer and poly(valerolactone)–poly(caprolactone)–poly(ethylene glycol)–poly(caprolactone)–poly(valerolactone) (PVL–PCL–PEG–PCL–PVL) pentablock copolymer were successfully prepared by ring-opening polymerization (ROP) of CL employing ITU/YCl₃ as catalyst in the presence of benzyl alcohol (BnOH) or poly(ethylene glycol) (PEG) as initiator, respectively. The reaction was systematically optimized, and the architecture, molecular weight and thermal properties of the polymers were characterized by NMR, FTIR, SEC and DSC analyses. Finally, a plausible polymerization mechanism was proposed.

The combined interaction of 2,3,6,7-tetrahydro-5H-thiazolo[3,2-a] pyrimidine (ITU) as the organocatalytic nucleophile with YCl₃ as Lewis acid cocatalyst, generating ITU/YCl₃, was employed for homo- and copolymerization of CL with VL.     

Ti surface doping of LiNi0.5Mn1.5O4−δ positive electrodes for lithium ion batteries

The particle surface of LiNi_0.5Mn_1.5O_4−δ (LNMO), a Li-ion battery cathode material, has been modified by Ti cation doping through a hydrolysis–condensation reaction followed by annealing in oxygen. The effect of different annealing temperatures (500–850 °C) on the Ti distribution and electrochemical performance of the surface modified LNMO was investigated. Ti cations diffuse from the preformed amorphous ‘TiO_x’ layer into the LNMO surface during annealing at 500 °C. This results in a 2–4 nm thick Ti-rich spinel surface having lower Mn and Ni content compared to the core of the LNMO particles, which was observed with scanning transmission electron microscopy coupled with compositional EDX mapping. An increase in the annealing temperature promotes the formation of a Ti bulk doped LiNi_(0.5−w)Mn_(1.5+w)−tTi_tO₄ phase and Ti-rich LiNi_0.5Mn_1.5−yTi_yO₄ segregates above 750 °C. Fourier-transform infrared spectrometry indicates increasing Ni–Mn ordering with annealing temperature, for both bare and surface modified LNMO. Ti surface modified LNMO annealed at 500 °C shows a superior cyclic stability, coulombic efficiency and rate performance compared to bare LNMO annealed at 500 °C when cycled at 3.4–4.9 V vs. Li/Li⁺. The improvements are probably due to suppressed Ni and Mn dissolution with Ti surface doping.

LiNi_0.5Mn_1.5O_4−δ surface is doped with Ti ion maintaining the spinel structure at 500 °C, higher annealing temperatures cause Ti diffusion from surface towards the core.     

Temperature independence of piezoelectric properties for high-performance BiFeO3–BaTiO3 lead-free piezoelectric ceramics up to 300 °C

The temperature-dependence behaviors of ferroelectric, piezoelectric, k_p and electrical-field-induced strain were carefully evaluated for high-performance BiFeO₃–0.3BaTiO₃ (BF–0.3BT) ceramics. There results indicate, combined with Rayleigh analysis and temperature-dependence XRD and PFM, that the increase of strain and large signal with increasing the temperature from room temperature to 180 °C is related to the joint effect of intrinsic contribution (lattice expansion) and extrinsic contribution (domain switching). With further increasing the temperature to 300 °C, the large signal d₃₃ and electrical-field-induced strain mildly decrease because of the increase of conductivity for BF–0.3BT ceramics. However, different from strain and large signal the small signal d₃₃(E₀) and k_p exhibit excellent temperature stability behavior as the temperature increases from room temperature to 300 °C.

The temperature-dependence behaviors of ferroelectric, piezoelectric, k_p and electrical-field-induced strain were carefully evaluated for high-performance BiFeO₃–0.3BaTiO₃ (BF–0.3BT) ceramics.     

Experimental study on light volatile products from thermal decomposition of lignin monomer model compounds: effect of temperature,residence time and methoxyl group

In order to investigate the effects of temperature, residence time (RT) and methoxyl (OCH₃) on the product distribution and vapor phase reactions during pyrolysis of complex solid fuels, three model phenolic representatives, phenol, guaiacol and syringol, were pyrolyzed at a residence time of 0.7 s, over a temperature range of 400 °C–950 °C, and at temperatures of 650 °C and 750 °C, in a RT region of 0.1 s–4.2 s. Increasing yields of CO and C₁–C₅ light hydrocarbons (LHs) with RT at 650 °C and 750 °C indicated that ring-reduction/CO elimination of phenolic compounds happened at 650 °C, and dramatically at 750 °C. The addition of OCH₃ affects the product distribution and ring-reduction pathways: C₅ LHs from phenol, C₂ LHs, C₄ LHs and C₅ LHs from guaiacol, and C₁–C₂ LHs from syringol. CO₂ yields increase with the addition of OCH₃. CO₂ was formed via benzoyl and a four-membered ring, which would compete with the CO formation. The addition of OCH₃ promotes the formation of coke and tar. The decomposition pathways are discussed, based on the experimental data, focusing on ring-reduction reactions and the formation of CO/CO₂ and C₁–C₅ LHs.

Effects of temperature, residence time and methoxyl on the decomposition of phenol, guaiacol and syringol, were investigated. Thermal decomposition pathways of the three model compounds were discussed based on ring reduction/CO elimination reactions.     

A concise and efficient total synthetic route of active stilbene dimer (±)-ε-viniferin

A concise and efficient procedure for the total synthesis of natural stilbene dimer (±)-ε-viniferin was accomplished with high overall yield. Demethylation of the key intermediate methyl 3-arylbenzofuran-4-carboxylate was achieved successfully through bromination followed by BBr₃-or BCl₃/TBAI-mediated ether cleavage reaction. Pd/C and bromobenzene-catalyzed MOM ether cleavage was successfully carried out to aquire (±)-ε-viniferin.

Demethylation of the key intermediate methyl 3-arylbenzofuran-4-carboxylate resulted in a concise and efficient procedure for the total synthesis of active natural stilbene dimer (±)-ε-viniferin with MOM as a protecting group.

Oligostilbenes are highly oxygenated natural products possessing more than two stilbene monomers and complex structures. The total synthesis of several oligostilbenes isolated from natural sources has been investigated in the past three decades due to their interesting structures and different biological activities.^1–7 (±)-ε-Viniferin (1), a natural resveratrol dimer containing the 2,3-diaryl-4-styryldihydrobenzofuran skeleton (Fig. 1), has been isolated from Vitaceaeous plants and determined to have potent activities, such as anti-inflammatory, antioxidant, antifungal, and anticancer.^8–13 However, only a few chemical approaches for this compound have been reported because of their unique carbon framework and structural instability.^14,15 Most of the attempts to prepare (±)-ε-viniferin derived from its presumed biogenesis, that is, oxidative dimerization of resveratrol, which led to the generation of its dimer (±)-ε-viniferin.^16–20 Several well-designed cascadse reactions and total synthesis methods for the chemically controlled synthetic routes are not readily applicable to the synthesis of (±)-ε-viniferin because of the insufficient regioselectivity and low yield.^6,7,21,22 Therefore, the development of an effective synthetic route for the preparation of (±)-ε-viniferin is of great important.Open in a separate windowFig. 1Structure of (±)-ε-viniferin (1).In 2009, Ikyon Kim and Jihyun Choi reported a versatile synthetic route to permethylated vinferifuan.²³ Encouraged by their work, Elofsson et al. investigated the total synthesis of (±)-ε-viniferin and reported a synthetic route with methyl, cyclopropylmethyl and acetyl as protecting group.²¹ However, the long reaction steps and multiple protecting group switch make their synthetic route unsuitable for specific alterations of substitution patterns. We also failed in our investigation on the total synthesis of (±)-ε-viniferin due to the unsuccessful demethylation of pentamethylated (±)-ε-viniferin in the last step.²²Considering the importance of (±)-ε-viniferin as an active lead compound and existing synthesis challenges, we continuously focused our attention on the total synthesis of (±)-ε-viniferin and its analogues. In this study, we report a practical total synthetic route of (±)-ε-viniferin on the basis of the exploration of the demethylation of methylated methyl 3-arylbenzofuran-4-carboxylate mediated by BBr₃ or BCl₃ under the assistance of bromination.In 2016, Elofsson and our group described two approaches to the synthesis of (±)-ε-viniferin with phenols protected as methyl or cyclopropylmethyl (cPrMe) ethers.^21,22 As outlined in Scheme 1, etherification of compounds 2 (or 2a) and 3 followed by dehydrative cyclization (or alkoxycarbonylation) generated the key intermediate 3-arylbenzofuran 4 (or 4a). Then, direct arylation of 4 (or 4a) produced the key intermediate 5 (or 5a), which was converted to methyl or cyclopropylmethyl ethers of (±)-ε-viniferin 6 (or 6a) through further elaboration. However, when 6 (or 6a) was treated with well-established techniques for ether cleavage, it was unexpectedly directly converted into (±)- ampelopsin F (7) or (±)-ampelopsin B (8) rather than into the desired target (±)-ε-viniferin (1). This result indicates that the conditions for removing the alkyl ether-protecting group were incompatible with the structure of 2,3-diaryl-4-styryldihydrobenzofuran. Hence, we realized that a different protecting group was necessary for the synthesis. Recently, we found that MOM as protecting group is easy to remove under the presence of Pd/C, bromobenzene, and hydrogen, but it has no effect on the 2,3-diaryl-4-styryldihydrobenzofuran skeleton. Comparison with acetyl group, MOM is able to tolerate the strong alkali conditions in the Horner–Wadsworth–Emmons-type olefination reaction. Its removal conditions is compatible with the 2,3-diaryl-4-styryldihydrobenzofuran skeleton. So, we envisioned that the MOM protecting group is suitable in the total synthesis of (±)-ε-viniferin.Open in a separate windowScheme 1Previous synthetic approach to stilbene dimers.Hence, we commenced our synthesis with the preparation of 2,3-diarylbenzofuran (5), which was prepared from the etherification of α-bromoketone 3 and phenol 9 with 98% yield in the presence of K₂CO₃, followed by Bi(OTf)₃-catalyzed dehydrative cyclization to produce 2-arylbenzofuran intermediate 4 with 81% yield, which was then converted to 5via direct arylation with 10 at the C2 position in 87% yield (Scheme 2).^22,23Open in a separate windowScheme 2Preparation of methylated arylbenzofuran 4 and diarylbenzofuran 5. Reagents and conditions: (a) K₂CO₃, acetone, CH₃I, r.t., 18 h, 42%; (b) K₂CO₃, acetone, reflux, 3 h, 98%; (c) Bi(OTf)₃, DCM, reflux, 23 h, 81%; (d) Pd(OAc)₂, PCy₃·HBF₄, Cs₂CO₃, Pivalic acid, DMA, 140 °C, 20 h, 87.0%.Next, we focused our effort on the demethylation of the key intermediate 2,3-diarylbenzofuran 5. When 5 was treated with BBr₃ in dichloromethane at −45 °C, followed by slow warming to room temperature overnight under nitrogen atmosphere, it was unexpectedly converted into Friedel–Crafts acylation product 11 rather than into the desired demethylation target molecule 15. Most well-established techniques for ether cleavage have been investigated, but none has been found to remove methyl groups with acceptable yield without Friedel–Crafts cyclization.^24–26 Even with the more stable tert-butyl ester 5b instead of methyl ester 5, the same results were obtained. In line with literature,²⁷ the acylation reaction occurred easily at the ortho-positions of 3,5-dimethoxyphenyl, which were prone to bromination. Moreover, the addition of halogen electrophile to alkenes was reversible. Initially, we envisaged that demethylation of 5 could be realized from bromide 12 through global demethylation and dehalogenation reactions. Exposure of 5 to 10 equivalent of Br₂ in CH₂Cl₂ at 0 °C provided 12 with three extra halogen attached in 80% yield, and subsequent demethylation of 12 with BBr₃ in CH₂Cl₂ under nitrogen atmosphere was achieved successfully to provide 13 in 39% yield. To our surprise, debromination of 13 in the presence of Pd/C under hydrogen atmosphere for 16 h produced only the monobrominated product 14 in 79% yield, but not the desired global dehalogenation product 15. The large steric hindrance at ortho-positions of 3,5-dimethoxyphenyl caused by the aromatic ring at C2 in 14 could be responsible for the results (Scheme 3).Open in a separate windowScheme 3Demethylation of diarylbenzofuran 5. Reagents and conditions: (a) BBr₃, DCM, N₂,−45 °C -r.t, overnight, 36%; (b) Br₂, DCM, 0 °C, 6 h, 80%; (c) BBr₃, DCM, N₂, −45 °C -r.t, overnight, 39%; (d) 10% Pd–C, H₂ (0.6 MPa), 16 h, 79%; (e) BCl₃, TBAI, Ar, 0 °C, 6 h, 65%.Afterward, we turned our attention to another intermediate 3-arylbenzofuran 4, which is theoretically the most likely to generate demethylated product 15. Exposure of 4 to 10 equivalent of bromine source in dichloromethane at 0 °C for 6 h afforded the desired bromide 16 with four extra halogen attached in 86% yield. From this bromide, BBr₃-catalyzed demethylation in CH₂Cl₂ at −45 to 0 °C and subsequent Pd/C-catalyzed hydrogenative debromination in methanol under hydrogen atmosphere were achieved smoothly to provide 17 and 18 with yields of 42% and 67%, respectively, as expected. When 18 was exposed to the conditions [Pd(OAc)₂, PCy₃·HBF₄Cs₂CO₃, pivalic acid, 19, DMA, 140 °C, 20 h] as reported by Zhang et al.,²² followed by Pd/C-catalyzed debenzylation reaction in ethanol under hydrogen atmosphere, the key intermediate 15 was obtained successfully with an overall yield of 44% in two steps (Scheme 4). Obviously, C2 arylation reaction of 18 also proceeded smoothly in the absence of protecting group for phenolic hydroxyls, although the yield is lower.Open in a separate windowScheme 4Demethylation of arylbenzofuran 4 and preparation of diarylbenzofuran 15. Reagents and conditions: (a) Br₂, DCM, 0 °C, 6 h, 86%; (b) BBr₃, DCM, −45 to 0 °C, overnight, 42%; (c) 10% Pd–C, H₂ (0.5 MPa), MeOH, 6 h, 67%; (d) Pd(OAc)₂, PCy₃·HBF₄, Cs₂CO₃, pivalic acid, DMA, 140 °C, 20 h; (e) 10% Pd–C, H₂ (0.5 MPa), EtOH, 6 h. 44% for two steps; (f) BBr₃, DCM, Ar, −20 to 0 °C, 6 h, 57%.However, the overall yield of 11% for 15 from 4 in four steps was too low to be acceptable. Through a series of investigations, combined with the methods reported in literature,^25,26 we found that under high-purity argon atmosphere, direct demethylation of 4 mediated by BBr₃ in CH₂Cl₂ at −20 °C to 0 °C produced the target 18 successfully with 57% yield (Scheme 4). Similarly, direct demethylation of 5 mediated by BCl₃/TBAI in CH₂Cl₂ at 0 °C under argon atmosphere produced the target 15 with 65% yield (Scheme 3). Evidently, both global demethylation reactions were implemented at high yields, and high-purity argon played an important role in the two reactions.With the key intermediate diarylbenzofuran 15 on hand, we explored the total synthesis of (±)-ε-viniferin. As mentioned above, identifying an applicable protecting group for phenolic hydroxyls is the critical issue in this synthesis. The group should be able to tolerate the strong alkali conditions in the Horner–Wadsworth–Emmons-type olefination reaction, and its removal conditions should be compatible with the 2,3-diaryl-4-styryldihydrobenzofuran skeleton. The protecting group MOM, which we found recently and proved to be easy to remove under mild conditions using Pd/C and bromobenzene under hydrogen atmosphere, should be suitable for this procedure. More importantly, its removing conditions has no effect on the reducible group (double bond) in (±)-ε-viniferin 1.Similar to literature,^6,22 when 15 was treated with triethylsilane in trifluoroacetic acid at 0 °C to room temperature overnight, dihydrobenzofuran 20 was obtained with 65% yield. Product 20 was then treated with MOMCl in the presence of Cs₂CO₃ in dry acetone at room temperature for 20 h to achieve MOM ether 21 with 97% yield. The methyl ester in 21 was subsequently reduced using LiAlH₄ in THF at room temperature, then reoxidized with Dess–Martin periodinane in dichloromethane overnight to produce aldehyde 22 with an overall yield of 66% in two steps. As expected, Horner–Wadsworth–Emmons-type olefination of 22 with diethyl 4-methoxymethoxy benzylphosphonate 23 in the presence of t-BuOK in THF at room temperature for 24 h successfully generated MOM ether 24 with 93% yield. Final deprotection of MOM ether 24 catalyzed by Pd/C and bromobenzene in MeOH under hydrogen atmosphere led to the production of (±)-ε-viniferin 1 in quantitative yield (97%, Scheme 5).Open in a separate windowScheme 5Synthesis of (±)-ε-viniferin. Reagents and conditions: (a) TFA, TES, 0 °C-r.t., overnight, 65%; (b) MOMCl, Cs₂CO₃, r.t., 20 h, 97%; (c) LiAlH₄, THF, MeOH, r.t., 6 h; Dess-Martin, DCM, r.t., overnight, 66% for two steps; (d) t-BuOK, THF, r.t., 24 h, 93%; (e) 10% Pd–C, PhBr, H₂ (0.5 MPa), MeOH, 5 h. 97%.In conclusion, we accomplished the total synthesis of resveratrol dimer (±)-ε-viniferin in 14 steps with an overall yield of 6.8%, through which a series of natural viniferin analogues could be prepared conveniently. Demethylation of the key intermediate methyl 3-arylbenzofuran-4-carboxylate was achieved through consecutive bromination, BBr₃-mediated direct demethylation, and dehalogenation catalyzed by Pd/C and hydrogen or BBr₃-and BCl₃/TBAI-mediated direct demethylation under argon atmosphere. Pd/C and bromobenzene-catalyzed MOM ether cleavage was successfully carried out to acquire (±)-ε-viniferin for the first time. The efficient procedure for the removal of the MOM group in the presence of reducible and acid-sensitive groups was meaningful, and it will be reported in due course.     

Microwave dielectric properties of low-temperature-fired MgNb2O6 ceramics for LTCC applications

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route. The effects of LMZBS addition on microwave dielectric properties, grain growth, phase composition and morphology of MgNb₂O₆ ceramics were studied. The SEM results show dense and homogeneous microstructure with grain size of 1.72 μm. Raman spectra and XRD patterns indicate the pure phase MgNb₂O₆ ceramic. The experimental results show that LMZBS glass can markedly decrease the sintering temperature from 1300 °C to 925 °C. Higher density and lower porosity make ceramics have better dielectric properties. The MgNb₂O₆ ceramic doped with 1 wt% LMZBS glass sintered at 925 °C for 5 h, possessed excellent dielectric properties: ε_r = 19.7, Q·f = 67 839 GHz, τ_f = −41.01 ppm °C⁻¹. Moreover, the favorable chemical compatibility of the MgNb₂O₆ ceramic with silver electrodes makes it as promising material for low temperature co-fired ceramic (LTCC) applications.

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route.     

β-Myrcene/isobornyl methacrylate SG1 nitroxide-mediated controlled radical polymerization: synthesis and characterization of gradient,diblock and triblock copolymers

β-Myrcene (My), a natural 1,3-diene, and isobornyl methacrylate (IBOMA), from partially bio-based raw materials sources, were copolymerized by nitroxide-mediated polymerization (NMP) in bulk using the SG1-based BlocBuilder™ alkoxyamine functionalized with an N-succinimidyl ester group, NHS-BlocBuilder, at T = 100 °C with initial IBOMA molar feed compositions f_IBOMA,0 = 0.10–0.90. Copolymer reactivity ratios were r_My = 1.90–2.16 and r_IBOMA = 0.02–0.07 using Fineman–Ross, Kelen–Tudos and non-linear least-squares fitting to the Mayo–Lewis terminal model and indicated the possibility of gradient My/IBOMA copolymers. A linear increase in molecular weight versus conversion and a low dispersity (Đ ≤ 1.41) were exhibited by My/IBOMA copolymerization with f_IBOMA,0 ≤ 0.80. My-rich and IBOMA-rich copolymers were shown to have a high degree of chain-end fidelity by performing subsequent chain-extensions with IBOMA and/or My, and by ³¹P NMR analysis. The preparation by NMP of My/IBOMA thermoplastic elastomers (TPEs), mostly bio-sourced, was then attempted. IBOMA-My-IBOMA triblock copolymers containing a minor fraction of My or styrene (S) units in the outer hard segments (M_n = 51–95 kg mol⁻¹, Đ = 1.91–2.23 and F_IBOMA = 0.28–0.36) were synthesized using SG1-terminated poly(ethylene-stat-butylene) dialkoxyamine. The micro-phase separation was suggested by the detection of two distinct T_gs at about −60 °C and +180 °C and confirmed by atomic force microscopy (AFM). A plastic stress–strain behavior (stress at break σ_B = 3.90 ± 0.22 MPa, elongation at break ε_B = 490 ± 31%) associated to an upper service temperature of about 140 °C were also highlighted for these triblock polymers.

β-Myrcene (My), a natural 1,3-diene, and isobornyl methacrylate (IBOMA), from partially bio-based raw materials sources, were copolymerized by nitroxide-mediated polymerization (NMP) in bulk.     

High temperature structure evolution of SiBZrOC quinary polymer derived ceramics

SiBZrOC quinary ceramics were obtained through the modification of a SiOC precursor with B(OH)₃ and Zr(OnPr)₄. The results showed that both B and Zr atoms were involved in the SiOC network through Si–O–B and Si–O–Zr bonds, respectively. The combined effects of B and Zr on the chemical structure and the thermal stability of the SiBZrOC system were investigated in detail. The sp³–C/Si ratio of SiBZrOC ceramics was between the values for SiZrOC and SiBOC. The presence of B promotes the crystallization of t-ZrO₂, which precipitated at 1000 °C and transformed to m-ZrO₂ at 1400 °C. At 1600 °C, ZrO₂ reacted with the matrix and formed ZrSiO₄, which consumed SiO₂ and thus inhibited the carbothermal reaction. The very small I(D)/I(G) ratio of 0.13 in the Raman spectra indicated the high graphitization of free carbon in SiBZrOC ceramics, which was observed by TEM with 10–20 graphene layers. The SiBZrOC ceramics showed excellent thermal stability in argon at 1600 °C for 5 h with a mass loss of 6%. Both the formation of ZrSiO₄ and the highly graphitized free carbon play important roles in inhibiting the carbothermal reaction and thus improving the thermal stability of SiBZrOC ceramics.

SiBZrOC quinary ceramics were obtained through the modification of a SiOC precursor with B(OH)₃ and Zr(OnPr)₄.     

pH-responsive polymeric vesicles from branched copolymers

A new type of branched copolymer, poly(l-lactide)₂-b-poly(l-glutamic acid) (PLLA₂–PLGA), based on polypeptide PLGA is synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG–NCA) with amino-terminated PLLA₂–NH₂ and subsequent deprotection. The branched copolymer is characterized by ¹H NMR, FTIR and GPC measurements. The self-assembly of the copolymers in aqueous media has been systematically discussed. A pyrene probe has been used to demonstrate the aggregated formation of PLLA₂–PLGA in solution by measuring the critical micelle concentration (cmc). The morphology and size of the micelles have further been studied by transmission electron microscopy (TEM), dynamic light scattering (DLS) and field emission scanning electron microscopy (ESEM). We demonstrated that the Rh of the vesicle is depending on solution pH and salt concentration. The vesicles show good stability with remained shapes and sizes during the lyophilizing process. These vesicles have great potential in the application of drug delivery.

A new type of branched copolymer, poly(l-lactide)₂-b-poly(l-glutamic acid), based on polypeptide PLGA is synthesized by the ring-opening polymerization of N-carboxyanhydride of γ-benzyl-l-glutamate with amino-terminated PLLA₂–NH₂ and subsequent deprotection.     

Enhancing the thermal stability of the carbon-based perovskite solar cells by using a CsxFA1−xPbBrxI3−x light absorber

Despite the impressive photovoltaic performance with a power conversion efficiency beyond 23%, perovskite solar cells (PSCs) suffer from poor long-term stability, failing by far the market requirements. Although many efforts have been made towards improving the stability of PSCs, the thermal stability of PSCs with CH₃NH₃PbI₃ as a perovskite and organic hole-transport material (HTM) remains a challenge. In this study, we employed the thermally stable (NH₂)₂CHPbI₃ (FAPbI₃) as the light absorber for the carbon-based and HTM-free PSCs, which can be fabricated by screen printing. By introducing a certain amount of CsBr (10%) into PbI₂, we obtained a phase-stable Cs_xFA_1−xPbBr_xI_3−x perovskite by a “two-step” method and improved the device power conversion efficiency from 10.81% to 14.14%. Moreover, the as-prepared PSCs with mixed-cation perovskite showed an excellent long-term stability under constant heat (85 °C) and thermal cycling (−30 °C to 85 °C) conditions. These thermally stable and fully-printable PSCs would be of great significance for the development of low-cost photovoltaics.

Mixed-cation Cs_xFA_1–xPbBr_xI_3–x perovskite was used as light absorber for the carbon-based perovskite solar cells, and the as-prepared solar devices showed excellent long-term stability under constant heat (85 °C) and thermal cycling (−30 °C to 85 °C) condition.     

One-step synthesis,characterization and properties of novel hybrid electromagnetic nanomaterials based on polydiphenylamine and Co–Fe particles in the absence and presence of single-walled carbon nanotubes

A one-step preparation method for hybrid electromagnetic nanomaterials based on polydiphenylamine (PDPA) and bimetallic Co–Fe particles in the absence and presence of single-walled carbon nanotubes (SWCNT) was proposed. During IR heating of PDPA in the presence of Co(ii) and Fe(iii) salts in an inert atmosphere at T = 450–600 °C, the polycondensation of diphenylamine (DPA) oligomers and dehydrogenation of phenyleneamine units of the polymer with the formation of C N bonds and reduction of metals by evolved hydrogen with the formation of bimetallic Co–Fe particles dispersed in a polymer matrix occur simultaneously. When carbon nanotubes are introduced into the reaction system, a nanocomposite material is formed, in which bimetallic Co–Fe particles immobilized on SWCNT are distributed in the matrix of the polymer. According to XRD data, reflection peaks of bimetallic Co–Fe particles at diffraction scattering angles 2θ = 69.04° and 106.5° correspond to a solid solution based on the fcc-Co crystal lattice. According to SEM and TEM data, a mixture of particles with sizes of 8–30 nm and 400–800 nm (Co–Fe/PDPA) and 23–50 nm and 400–1100 nm (Co–Fe/SWCNT/PDPA) is formed in the nanocomposites. The obtained multifunctional Co–Fe/PDPA and Co–Fe/SWCNT/PDPA nanomaterials demonstrate good thermal, electrical and magnetic properties. The saturation magnetization of the nanomaterials is M_S = 14.99–31.32 emu g⁻¹ (Co–Fe/PDPA) and M_S = 29.48–48.84 emu g⁻¹ (Co–Fe/SWCNT/PDPA). The electrical conductivity of the nanomaterials reaches 3.5 × 10⁻³ S cm⁻¹ (Co–Fe/PDPA) and 1.3 S cm⁻¹ (Co–Fe/SWCNT/PDPA). In an inert medium, at 1000 °C the residue is 71–77%.

In a self-organizing system within one stage under IR heating conditions, hybrid nanomaterials are formed with a structure that contains bimetallic Co–Fe particles, free or immobilized on the SWCNT surface, dispersed in the polymer PDPA matrix.     

Effective doping control in Sm-doped BiFeO3 thin films via deposition temperature

Sm-doped BiFeO₃ (Bi_0.85Sm_0.15FeO₃, or BSFO) thin films were fabricated on (001) SrTiO₃(STO) substrates by pulsed laser deposition (PLD) over a range of deposition temperatures (600 °C, 640 °C and 670 °C). Detailed analysis of their microstructure via X-ray diffraction (XRD) and transmission electron microscopy (TEM) shows the deposition temperature dependence of ferroelectric (FE) and antiferroelectric (AFE) phase formation in BSFO. The Sm dopants are clearly detected by high-resolution scanning transmission electron microscopy (HR-STEM) and prove effective in controlling the ferroelectric properties of BSFO. The BSFO (T_dep = 670 °C) presents larger remnant polarization (Pr) than the other two BSFO (T_dep = 600 °C, 640 °C) and pure BiFeO₃ (BFO) thin films. This study paves a simple way for enhancing the ferroelectric properties of BSFO via deposition temperature and further promoting BFO practical applications.

Sm-doped BiFeO₃ (Bi₀.₈₅Sm_0.15FeO₃) thin films were fabricated on (001) SrTiO₃ substrates by PLD over a range of deposition temperatures. The Sm dopants are clearly detected by high-resolution scanning transmission electron microscopy.

As a promising alternative lead-free piezoelectric material, BiFeO₃ (BFO) thin films have attracted enormous research interest due to their remarkable multiferroic properties and piezoelectric response.^1–4 However, the high leakage current and large coercive field are factors limiting the extensive use of BFO.⁵ Since the polarization is mainly induced by the Bi³⁺ ions, various rare-earth elements (e.g., La, Nd, Sm, and Gd) have been doped into the Bi-site to improve the overall ferroelectric response.^6–8 According to the site-engineering concept, the doping of foreign elements causes chemical pressure and controls the volatility of Bi atoms in BFO systems.^9,10 The structural information of rare-earth-doped BFO (Re-BFO) systems is therefore upgraded and a preliminary phase diagram is proposed.^11–14Sm-doped BFO (Bi_1−xSm_xFeO₃, BSFO) thin film has attracted research attention, due to the narrow concentration range at room temperature.¹⁵ It shows ferroelectric (FE) rhombohedral to antiferroelectric (AFE) orthorhombic phase transitions as the Sm doping amount increases. Morphotropic phase boundary (MPB) appears at around x = 0.13–0.15, and high values of out-of-plane piezoelectric coefficient (d₃₃ ∼ 110 pm V⁻¹) and enhanced dielectric constant at x = 0.14 are reported in such systems.^16,17 Structure studies show that three main phase, FE R3c phase, AFE PbZrO₃-like phase, and paraelectric Pnma phase, coexist at the MPB composition.¹⁸ In this regard, many efforts have been made on the investigation of phase transitions under external stimuli.^19,20 However, there are not much work on the structure analysis of BSFO at the atomic-scale level. It will be interesting to investigate the microstructure with high-resolution transmission electron microscopy (TEM) and high-resolution scanning transmission electron microscopy (HR-STEM). The detailed microstructure information will reveal how the Sm dopants distribute in the overall BSFO lattice. In addition, BSFO films in previous studies are mostly prepared by solid phase synthesis and sol–gel method^15,20,21 with very few reports using pulsed laser deposition (PLD).^17,22 In those prior reports, Sm-doping amounts in films were controlled by changing the composition of the deposition targets. Deposition temperature has been proven as an effective parameter for PLD in controlling the doping amount, thin film microstructure and the related properties. In the Ag-doped ZnO (SZO) system, deposition temperature was directly used to control the density of stacking faults and consequently affect the electrical transport properties.²³ Table S1^† lists several reported deposition temperatures for Re-BFO thin films, which is in the range of 520 °C to 850 °C. Here, we used three different substrate temperatures, 600 °C, 640 °C and 670 °C, for the BSFO film fabrication via PLD. Pure BFO film was also grown as a reference sample for comparison. Besides the detailed microstructure, the corresponding ferroelectric property measurements were conducted on the BSFO thin films to investigate how the Sm dopants affect the ferroelectric behavior of BSFO.In the present work, Bi_0.85Sm_0.15FeO₃ (BSFO) was selected as the model system. The BSFO target was synthesized by a conventional solid-state sintering method using high-purity Bi₂O₃ (99.99%), Fe₂O₃ (99.95%) and Sm₂O₃ (99.90%) powders. Thin films were grown on (001) single-crystal SrTiO₃ (STO) substrates epitaxially via PLD. KrF excimer laser with a wavelength of 248 nm was used as the laser source. Three different substrate temperatures, 600 °C, 640 °C and 670 °C, were applied in the deposition. For all depositions, oxygen partial pressure was kept at 200 mTorr and the deposition rate was 5 Hz. The films were cooled down to room temperature at a cooling rate of 10 °C min⁻¹ in 200 torr oxygen atmospheres. The growth condition and parameters of BFO film is same with our previous report.²⁴ Au top contacts with 100 nm thickness and 0.1 mm² were deposited by a custom-built magnetron sputtering system. The Au sputter target (99.99% pure) is made by Williams Advanced Materials.X-ray diffraction (XRD) spectra were collected by a PANalytical Empyrean system using Cu K_α radiation. The Raman spectra were measured by Renishaw''s inVia Raman microscope. The microstructure analysis was performed on FEI TALOS F200X TEM/STEM operated at 200 kV. The energy-dispersive X-ray spectroscopy (EDS) chemical mapping was acquired by the SuperX EDS system with four silicon drift detectors. Ferroelectric characterization was conducted by Precision LC II Ferroelectric Tester (Radiant Technologies, Inc.). Fig. 1(a) shows the θ–2θ XRD spectra of the as-prepared thin film samples deposited at 600 °C, 640 °C and 670 °C. All the films display BSFO (00l) diffraction peaks, indicating highly textured BSFO along c-axis. It is noted that BSFO (003) peak shifts from 71.62°, to 70.82° and to 70.70° with the deposition temperature increasing from 600 °C to 640 °C, and 670 °C. The corresponding out-of-plane lattice parameters are calculated to be 3.951 Å, 3.987 Å and 3.993 Å, respectively and are summarized in Fig. 1(b). Compared with the out-of-plane lattice parameter of pure BFO film (∼4.000 Å) on STO substrate,²⁴ three BSFO samples show smaller lattice parameters than that of pure BFO. This is because partial Bi³⁺ (radius = 1.030 Å) ions have been substituted by Sm³⁺ ions with smaller radius (radius = 0.958 Å).²⁵ The BSFO peak at around 32.155° (denoted as “*”) in Fig. 1(a) comes from rhombohedral (110) peak and the peak disappears when the deposition temperature increases to 670 °C. The above results indicate that the deposition temperature influences the Sm-doping amount and the BSFO crystal structure. Raman analysis has been conducted on all BSFO and pure BFO films. The Raman spectra were fitted with Lorentzian curves, as shown in Fig. S1.^† The reported data of bulk polycrystalline Bi_1−xSm_xFeO₃ was taken as reference.²⁶ The overall shape of peaks is the same, which implies that the main structure of BSFO sample is the same as the rhombohedral R3c structure of BFO.Open in a separate windowFig. 1(a) θ–2θ XRD spectra of BSFO film deposited at 600 °C, 640 °C and 670 °C. (b) The summary of out-of-plane lattice parameter. (c–e) Reciprocal space map (RSM) results of BSFO (103) peaks.To further analyze the detailed phase information, asymmetric reciprocal space mapping (RSM) measurements were performed around the (103) diffraction peak for all the three BSFO samples and the results are shown in Fig. 1(c)–(e). The RSM pattern of sample (T_dep = 600 °C) exhibits four domains, which are shown by red triangles. It indicates the existence of rhombohedral-like phase which has antipolar nature.^27–29 For the other two samples (T_dep = 670 °C and T_dep = 640 °C), peak split along Q_x direction is not apparent and the narrower width along Q_x direction is observed, indicating less structure distortion in BSFO films deposited at higher temperature. These results provide direct evidence that the deposition temperature significantly affects the domain structure of the BSFO film.In order to analyze the microstructure structure, TEM analysis has been applied on two samples (T_dep = 670 °C and T_dep = 600 °C). Fig. 2(a) and (c) show the overall films stacks of BSFO on STO substrates. The corresponding selected area electron diffraction (SAED) patterns of BSFO thin films only demonstrate the rhombohedral-like phases. It is interesting to note that the TEM image of high deposition temperature sample (T_dep = 670 °C) exhibits few dark lines. And the dark line density in the high deposition temperature sample is obviously higher than that in the lower deposition temperature one. The image contrast is proportional to ∼Z² (Z, atomic number) in TEM bright-field mode. The dark line is therefore proposed be related with Sm, owing to Z_Sm is larger than Z_Bi and Z_Fe. It also suggests that the higher deposition temperature introduce more Sm dopants in BSFO films than the lower one. The Fig. 2(b) and (d) are high resolution TEM (HR-TEM) images from local areas, which were analyzed by Fast Fourier Transform (FFT). The spots (marked by red arrows) in the FFT image of the sample (T_dep = 670 °C) correspond to the incommensurate phase, which is caused by the competition between ferroelectric (FE) and antiferroelectric (AFE) phases. Different phase emerges in the sample (T_dep = 600 °C), and the corresponding spots are marked by red circle. It has been proved as the antipolar orthorhombic AFE phase, linked to the macroscopic AFE behavior. The phase information of Bi_0.85Sm_0.15FeO₃ thin film in this study is different from previous reported BSFO with only AFE phases.¹⁶ The above microstructure analysis shows the effect of deposition temperature on the phase formation in BSFO system even with 15 atomic percent Sm.Open in a separate windowFig. 2(a and c) Cross-sectional TEM images of BSFO thin films (670 °C and 600 °C) on STO substrates. (b and d) High resolution TEM images. The insets in (a and c) show the corresponding (SAED) pattern of BSFO thin films. The insets in (b and d) show the fast-Fourier transformed (FFT) images from the blue squared region.STEM analysis was then performed to resolve the composition information. Fig. 3(a) shows the high-resolution STEM (HR-STEM) image of the 670 °C sample. The high angle annular dark field mode (HADDF) image intensity is proportional to the atomic number Z. Thus, the white line areas in STEM image correspond to the dark lines in TEM images. We further examined the composition distribution across this Sm layer using the intensity line profile (Fig. 3(b)), which provides a direct interpretation of composition information in the HAADF imaging mode. It is obvious that the position near white line area has higher intensity than other areas. This result proves that Sm³⁺ ion has been doped into BFO system effectively. Energy dispersive spectroscopy (EDS) measurements have been further applied on the same area. The EDS mapping of Bi and Sm elements are shown in Fig. S2(b) and (c).^† The EDS line-scan analysis of Sm is overlaid on the HADDF image and displayed in Fig. S2(a).^† The line profile reflects high content of Sm corresponding to the white line area. Therefore, both the TEM and STEM results show that the higher deposition temperature BSFO sample (T_dep = 670 °C) has higher Sm-doping amount.Open in a separate windowFig. 3(a) HR-STEM image of BSFO film deposited at 670 °C. (b) Enlarged view of the yellow dashed square area from (a). The intensity line profile is inserted along the marked blue line.The ferroelectric behaviors were characterized by the polarization–electric field (P–E) hysteresis loops. Fig. 4(a)–(c) show the P–E loops of BSFO samples with three different deposition temperatures, while Fig. 4(d) shows the loop of pure BFO as a comparison. The polarization measurement as a function of electric field measurement was carried out at room temperature for several times to ensure the reproducibility of the measurements. The BSFO sample (T_dep = 670 °C) with higher Sm-doping amount exhibits obvious enhanced polarization. The remnant polarization (Pr) for the film is determined to be 17 μC cm⁻², much larger than other two BSFO samples and the BFO sample. It was proposed that the incorporation of Sm could break the short-range dipolar regions, surmount the local barrier and transform it to the long-range polar structure.³⁰ The BFO film with four-variant domains exhibits a lower electric filed and remnant polarization Pr.³¹ It was also found that the formation of bridging phase could enhance piezoelectric and dielectric properties of BSFO.¹⁶ In this work, the BSFO sample (T_dep = 600 °C) shows four structural domain structure and the lowest Pr. With the increase amount of Sm-doping amount, incommensurate phase appears in the 670 °C sample. We conclude that the higher deposition temperature introduces the higher Sm-doping amount, which further assists the incommensurate phase formation and suppresses the AFE phase. In addition, the unsaturated P–E loop of BFO film indicates it suffers from high leakage current, which is generally due to the appearance of Bi deficiencies and oxygen vacancies.³² The Sm–O bond enthalpy (565 ± 13 kJ mol⁻¹) is stronger than the Bi–O bond enthalpy (337 ± 12.6 kJ mol⁻¹).³³ Therefore, the higher polarization exhibited by BSFO samples (T_dep = 670 °C) than the pure BFO proves that the Sm dopant could compensate for the Bi loss and suppress the formation of oxygen vacancies. The P–E loop results were compared with prior reports on Re-BFO films. As shown in Table S1,^† the remnant polarization is quite different for Re-BFO systems. It is due to the different ionic radii of the rare earth elements, which result in different structural distortion of BFO and diverse critical doping ratio for phase transitions. Besides the phase variants, the polarization is closely related with the orientation of crystalline structures.Open in a separate windowFig. 4(a–c) Polarization hysteresis measurements for BSFO film deposited at 670 °C, 640 °C and 600 °C. (d) Polarization hysteresis measurements for BFO film.This study demonstrates that Sm-doping amount in BSFO thin films can be effectively tuned via deposition temperature. The Sm dopants influence phase formation of BSFO and further control the macroscopic ferroelectric properties. The local incommensurate phase presented by Bi_0.85Sm_0.15FeO₃ with higher Sm-doping amount than the reported ones (Bi_0.86Sm_0.14FeO₃), which is extremely helpful in constructing phase diagram of BSFO. More interestingly, the existence and location of Sm dopants in BSFO thin film have been directly demonstrated by the HR-STEM and corresponding EDS analysis. This work is also beneficial for the exploration of other Re-BFO films with deposition temperatures and detailed structure analysis, which is an important step toward the practical applications of Re-BFO in electronic devices.