Multifunctional Nd3+ substituted Na0.5Bi0.5TiO3 as lead-free ceramics with enhanced luminescence,ferroelectric and energy harvesting properties

Herein, we present comprehensive investigations of the optical and electrical properties of Nd³⁺ substitution in sodium bismuth titanate ceramics (NBNT) with varying Nd³⁺ concentration. The room temperature photoluminescence (PL) emission for both unpoled and poled samples is observed to be a maximum for an Nd³⁺ substitution of 1 mol%. Upon poling, the PL intensity is observed to be quenched, consistent with the obtained XRD data, indicating an electric-field induced structural ordering towards higher symmetry, confirmed with the help of structural refinement. The evaluated ferroelectric to relaxor and antiferroelectric relaxor T_(F–R) was observed clearly from the poled dielectric–loss curve for the 1 mol% of Nd³⁺ substitution. Furthermore, the optimized NBNT exhibited a lower E_c and a higher off-resonance figure of merit (FOM_off) for energy harvesting by 12% and 30%, respectively, in comparison with un-doped NBT.

Herein, we present investigations on the effect of electrical poling on the optical and electrical properties of Nd³⁺ substituted NBT ceramics with varying Nd³⁺ concentrations.     

High electrostrictive properties and energy storage performances with excellent thermal stability in Nb-doped Bi0.5Na0.5TiO3-based ceramics

As a promising candidate material replacing Pb(ZrTi)O₃ (PZT), the lead-free Bi_0.5Na_0.5TiO₃ (BNT) system exhibits outstanding piezoelectric and ferroelectric properties. However, the weak thermal stability of these electric properties hampers its practical applications. In this work, we designed and prepared novel Nb-doped 0.76Bi_0.5Na_0.5TiO₃–0.24Bi_0.5K_0.5TiO₃ (BNT–BKT) ceramics with superior temperature stability of electric properties. Both strain as well as discharging properties of 5% Nb-doped BNT–BKT ceramics varied less than 3% and 12.5% respectively from room temperature to 160 °C, ascribed to the enlarged gap between the depolarized temperature (T_d or T_F–R) and the maximum dielectric temperature (T_m). In addition, we investigated the impacts of Nb doping on the phase transition, dielectric, piezoelectric and ferroelectric behaviors of BNT–BKT ceramics in detail. Temperature dependent dielectric spectrums indicated that T_d decreased below room temperature with Nb modifying, revealing that the phase structure transformed from ferroelectric into ergodic relaxor. Accordingly, the maximum strain value of 0.21% and recoverable energy storage of 1.2 J cm⁻³ were simultaneously acquired at the critical composition of 5% Nb incorporation. Our results provide an effective means of obtaining BNT-based ceramics with simultaneously thermally stable strain and discharge properties for wide temperature actuator and capacitor applications.

Lowering T_d to enlarge the temperature range between T_d and the maximum dielectric temperature (T_m) proved to be an effective strategy to enhance the thermal stability strain and energy storage properties in BNT-based ceramics.     

Structural,electrical, and multiferroic characteristics of lead-free multiferroic: Bi(Co0.5Ti0.5)O3–BiFeO3 solid solution

A solid solution of bismuth cobalt titanate [Bi(Co_0.5Ti_0.5)O₃] and bismuth ferrite (BiFeO₃) with a composition Bi(Co_0.40Ti_0.40Fe_0.20)O₃ (abbreviated as BCTF80/20) was synthesized via a cost effective solid-state technique. Phase identification and basic structural symmetry of the samples were determined by analyzing powder X-ray diffraction data. Field emission scanning electron micrograph (FE-SEM) and energy dispersive X-ray (EDX) spectra were analyzed to evaluate the micro-structural aspects (shape and size, distribution of grains) as well as a quantitative evaluation of the sample. The average crystallite (particle) and grain size were found to be ∼30 nm and ∼1–2 micron, respectively. The electrical parameters (dielectric constant, tangent loss, impedance, modulus, and conductivity) of as-synthesized material were obtained in a temperature range of 300 to 773 K and frequency range of 1 kHz and 1000 kHz. The strong correlation of microstructure (i.e., grains, grain boundary, etc.) and electrical parameters of this material were observed. The frequency dependence of electrical impedance and modulus exhibited a deviation from an ideal Debye-like relaxation process. The dependence of dielectric relaxation mechanism on frequency and temperature is discussed in detail. The field dependent polarization (P–E hysteresis loop) of BCTF80/20 exhibited an enhanced value of remnant polarization as compared to that of BiFeO₃ (referred as BFO). At room temperature (300 K), the magnetic hysteresis loop measurements also showed a significant improvement in the magnetization of BCTF80/20. Thus, based on these enhanced values of remnant polarization and magnetic parameters, we can assume that BCTF80/20 may be considered as a promising candidate for some new generations of electronic devices.

A solid solution of bismuth cobalt titanate [Bi(Co_0.5Ti_0.5)O₃] and bismuth ferrite (BiFeO₃) with a composition Bi(Co_0.40Ti_0.40Fe_0.20)O₃ (abbreviated as BCTF80/20) was synthesized via a cost effective solid-state technique.     

Structure,dielectric, and piezoelectric properties of K0.5Na0.5NbO3-based lead-free ceramics

Lead-free ceramics based on the (1 − x)K_0.5Na_0.5NbO₃–xBi(Zn_0.5Ti_0.5)O₃ (KNN–BZT) system obtained via the conventional solid-state processing technique were characterized for their crystal structure, microstructure, and electrical properties. Rietveld analysis of X-ray diffraction data confirmed the formation of a stable perovskite phase for Bi(Zn_0.5Ti_0.5)O₃ substitutions up to 30 mol%. The crystal structure was found to transform from orthorhombic Amm2 to cubic Pm$\bar{3}$m through mixed rhombohedral and tetragonal phases with the increase in Bi(Zn_0.5Ti_0.5)O₃ content. Temperature-dependent dielectric behavior indicated an increase in diffuseness of both orthorhombic to tetragonal and tetragonal to cubic phase transitions as well as a gradual shift towards room temperature. The sample with x ≈ 0.02 exhibited a mixed rhombohedral and orthorhombic phase at room temperature. A high-temperature X-ray diffraction study confirmed the strong temperature dependence of the phase coexistence. The sample with the composition 0.98(K_0.5Na_0.5NbO₃)–0.02(BiZn_0.5Ti_0.5O₃) showed an improved room temperature piezoelectric coefficient d₃₃ = 109 pC/N and a high Curie temperature T_C = 383 °C.

Room temperature powder X-ray diffraction patterns of (1 – x)K_0.5Na_0.5NbO₃–xBi(Zn_0.5Ti_0.5)O₃ system.     

Composition design,electrical properties,and temperature stability in (1 − x)K0.44Na0.56Nb0.96Sb0.04O3-xBi0.45La0.05Na0.5ZrO3 lead-free ceramics

In this work, we designed a new system of (1 − x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ (KNNS-xBLNZ, 0 ≤ x ≤ 0.06) ceramics, and systemically investigated both their electrical performance and temperature stability. Through optimizing the composition, a relatively good comprehensive performance (e.g., d₃₃ ∼ 455 ± 10 pC N⁻¹, k_p ∼ 0.47 ± 0.02, T_C ∼ 266 °C, strain ∼ 0.148%, and ) is obtained in the ceramics with x = 0.040, which is attributed to the construction of a rhombohedral–orthorhombic–tetragonal (R–O–T) phase boundary. Moreover, a good temperature stability of remnant polarization (P_r) as well as strain value (P_{r100 °C}/P_rRT ∼ 89.6%, P_{r180 °C}/P_rRT ∼ 73.2%, S_{100 °C}/S_RT ∼ 92.6%, S_{180 °C}/S_RT ∼ 74.1%) is gained in KNNS-0.040BLNZ ceramics with a broad temperature range from room temperature to 180 °C. Hence, we believe that KNNS-xBLNZ ceramics opens a window for the practical application of lead-free ceramics.

A new system of (1 – x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ (KNNS-xBLNZ, 0 ≤ x ≤ 0.06) ceramics was designed, and systemically investigated both their electrical performance and temperature stability.     

Correction: Composition design,electrical properties,and temperature stability in (1 − x)K0.44Na0.56Nb0.96Sb0.04O3-xBi0.45La0.05Na0.5ZrO3 lead-free ceramics

Correction for ‘Composition design, electrical properties, and temperature stability in (1 − x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ lead-free ceramics’ by Jian Ma et al., RSC Adv., 2018, 8, 29871–29878.

The authors regret that an incorrect version of Fig. 4 was included in the original article. The correct version of Fig. 4 is presented below.Open in a separate windowFig. 1FE-SEM surface images of (1 − x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ ceramics with (a) x = 0, (b) x = 0.020, (c) x = 0.040, (d) x = 0.060.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Composition-induced phase evolution and high strain response in Ba(Zn1/3Nb2/3)O3-modified (Bi0.5Na0.5)TiO3-based lead-free ferroelectrics

In this work, a paraelectric complex perovskite Ba(Zn_1/3Nb_2/3)O₃ (BZN) was introduced into the morphotropic boundary composition (Bi_0.5Na_0.5)_0.93Ba_0.07TiO₃ (BNBT) to modulate the phase structure and electrical properties as well as the field-induced strain behavior. Using a columbite route, the ceramics with pure perovskite structure were successfully fabricated. The structure and electrical measurements showed that the introduction of BZN into BNBT results in the decrease of the rhombohedrality 90-γ, and promotes the evolution from ferroelectric to antiferroelectric (AFE) relaxor. Besides, the introduction of BZN induces the volume increase and dimension reduction of the nanosized AFE relaxor domains. A large field-induced strain of 0.39% with good stability against frequency, field, and temperature was obtained at the BNZ addition of composition x = 0.01, which locates at the critical composition boundary between ferroelectric state and AFE relaxor state.

Addition of 1.0 mol% Ba(Zn_1/3Nb_2/3O₃) into (Bi_0.5Na_0.5)_0.93Ba_0.07TiO₃ results in the decrease of the rhombohedrality and the evolution from ferroelectric to antiferroelectric relaxor, thus leads to the emergence of a large field-induced strain of 0.39%.     

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.     

Effect of Bi2O3 content on the microstructure and electrical properties of SrBi2Nb2O9 piezoelectric ceramics

Lead-free ceramics, SrBi₂Nb₂O₉–xBi₂O₃ (SBN–xBi), with different Bi contents of which the molar ratio, n(Sr) : n(Bi) : n(Nb), is 1 : 2(1 + x/2) : 2 (x = −0.05, 0.0, 0.05, 0.10), were prepared by conventional solid-state reaction method. The effect of excess bismuth on the crystal structure, microstructure and electrical properties of the ceramics were investigated. A layered perovskite structure without any detectable secondary phase and plate-like morphologies of the grains were clearly observed in all samples. The value of the activation energy suggested that the defects in samples could be related to oxygen vacancies. Excellent electrical properties (e.g., d₃₃ = 18 pC N⁻¹, 2P_r = 17.8 μC cm⁻², ρ_rd = 96.4% and T_c = 420 °C) were simultaneously obtained in the ceramic where x = 0.05. Thermal annealing studies indicated the SBN–xBi ceramics system possessed stable piezoelectric properties, demonstrating that the samples could be promising candidates for high-temperature applications.

Lead-free ceramics, SrBi₂Nb₂O₉–xBi₂O₃ (SBN–xBi), with different Bi contents of which the molar ratio, n(Sr) : n(Bi) : n(Nb), is 1 : 2(1 + x/2) : 2 (x = −0.05, 0.0, 0.05, 0.10), were prepared by conventional solid-state reaction method.     

Electrical properties of Sb2O3-modified BiScO3–PbTiO3-based piezoelectric ceramics

Compared with pure Pb-based perovskite ferroelectric materials, BiMeO₃–PbTiO₃ (Me = Sc³⁺, In³⁺, and Yb³⁺) systems have remarkable advantages in their Curie temperatures. As a member of this group, the BiScO₃–PbTiO₃ (BS–PT) solid solution has drawn considerable attention from scientists for its high Curie temperature and excellent piezoelectric coefficient. However, BS–PT ceramics still have some shortcomings, such as high dielectric loss and low mechanical quality factor, which make them unsuitable for high-temperature applications. Herein, we report the effect of the addition of complex ions on the electrical properties of BS–PT ceramics. Sb₂O₃-doped 0.36BiScO₃–0.64PbTi_0.97Fe_0.03O₃ + 1 mol% MnO₂ (BS–PTFMn + x% Sb₂O₃) ceramics were fabricated and their electrical properties were studied. BS–PTFMn + 0.75% Sb₂O₃ had an optimal piezoelectric coefficient, exhibiting which indicates that Sb₂O₃ doping can improve the piezoelectric properties of the BS–PT ceramics, exhibiting a “soft” effect of Sb₂O₃ doping. In addition, the thermal depolarization temperature (T_d) of BS–PTFMn + 0.75% Sb₂O₃ ceramics remained above 300 °C, such as 325 °C for BS–PTFMn + 0.75% Sb₂O₃. It was concluded that the piezoelectric properties of BS–PT ceramics were enhanced by the addition of Sb₂O₃.

Compared with pure Pb-based perovskite ferroelectric materials, BiMeO₃–PbTiO₃ (Me = Sc³⁺, In³⁺, and Yb³⁺) systems have remarkable advantages in their Curie temperatures.     

A modified random network model for P2O5–Na2O–Al2O3–SiO2 glass studied by molecular dynamics simulations

We investigated the short- and medium-range structural features of sodium aluminosilicate glasses with various P₂O₅ (0–7 mol%) content and Al/Na ratios ranging from 0.667 to 2.000 by using molecular dynamics simulations. The local environment evolution of network former cations (Si, Al, P) and the extent of clustering behavior of modifiers (Na⁺) is determined through pair distribution function (PDF), total correlation function (TDF), coordination number (CN), Q_xⁿ distribution and oxygen speciation analysis. We show that Al–O–P and Si–O–Al linkage is preferred over other connections as compared to a random model and that Si–O–Si linkage is promoted by the P₂O₅ addition, which is related to structural heterogeneity and generates well-separated silicon-rich and aluminum–phosphorus-rich regions. Meanwhile, due to the relatively high propensity of Al to both Si and P, heterogeneity can be partly overcome with high Al content. A small amount of Si–O–P linkages have been detected at the interface of separated regions. Clustering of Na⁺ is also observed and intensified with the addition of P₂O₅. Based on the simulated structural information, a modified random network model for P₂O₅-bearing sodium aluminosilicate glass has been proposed, which could be useful to optimize the mobility of sodium ions and design novel functional glass compositions.

(A) A modified structural model proposed for P₂O₅-bearing sodium aluminosilicate glasses. (B) Degree of preferred connection (DPC) of different T–O–T network linkage for LAP, MAP and HAP glass compositions with various P₂O₅ content.     

The preparation,microstructure and mechanical properties of a dense MgO–Al2O3–SiO2 based glass-ceramic coating on porous BN/Si2N2O ceramics

A dense MgO–Al₂O₃–SiO₂ based glass-ceramic coating was prepared by a doctor blade process on a porous BN/Si₂N₂O ceramic surface followed by heat treatment at 1050 °C under nitrogen flow. The phase composition, microstructure, mechanical properties and water absorption of the coating were studied. The coating consisted of α-cordierite phase with a small amount of glass phase. The dense coating without pores and cracks was favorable to seal and densify the porous ceramic surface due to part of the molten glass infiltrating the surface pores. The coating was defect-free and tightly bonded to the substrate because of a larger bonding area between the coating and the substrate. The elastic modulus and bending strength of the glass-ceramic coating were 37.9 GPa and 67.1 MPa, respectively. Moreover, the coated samples had a high Vickers hardness and low water absorption.

A dense MgO–Al₂O₃–SiO₂ based glass-ceramic coating was prepared by a doctor blade process on a porous BN/Si₂N₂O ceramic surface followed by heat treatment at 1050 °C under nitrogen flow.     

Improvements in piezoelectric and energy harvesting properties with a slight change in depolarization temperature in modified BNKT ceramics by a simple technique

For many BNT-based ceramics, an attempt to increase the piezoelectric properties usually results in a decrease in depolarization temperature (T_d). This trend limits the applications of the materials. Many previous experiments have used different methods to enhance the piezoelectric properties and improve the T_d characteristic. In this study, we demonstrated a simple technique (thermal annealing) to enhance the piezoelectric properties with a very slight decrease in T_d by ∼2 °C for a modified BNKT ceramic (BNKT doped with ZnO). Other phase transition characteristic temperatures of the studied ceramics were also slightly changed. The optimum dielectric (ε_r = 651, tan δ = 0.0503, T_F–R = 167.38 °C, T_m = 305.41 °C, ε_max = 5551, T_B = 367.15 °C, T_d = 155.98 °C, and γ = 1.43), ferroelectric (P_max = 41.28 μC cm⁻², P_r = 35.85 μC cm⁻², E_c = 42.60 kV cm⁻¹ and R_sq = 1.42), piezoelectric (d₃₃ = 198 pC N⁻¹, k_p = 0.598, and g₃₃ = 34.35 × 10⁻³ Vm N⁻¹), and energy harvesting (FoM = 6.80 pm² N⁻¹) were obtained for the 8 h annealed ceramic. Furthermore, higher energy harvesting properties (which were 32% higher than that of the unannealed ceramic) were obtained after employing this technique.

In this study, we demonstrated a simple technique (thermal annealing) to enhance the piezoelectricity with a very slight decrease in T_d by ∼2 °C for a modified BNKT ceramic (BNKT doped with ZnO).     

Ni nanocatalysts supported on mesoporous Al2O3–CeO2 for CO2 methanation at low temperature

The selectivity and activity of a nickel catalyst for the hydrogenation of carbon dioxide to form methane at low temperatures could be enhanced by mesoporous Al₂O₃–CeO₂ synthesized through a one-pot sol–gel method. The performances of the as-prepared Ni/Al₂O₃–CeO₂ catalysts exceeded those of their single Al₂O₃ counterpart giving a conversion of 78% carbon dioxide with 100% selectivity for methane during 100 h testing, without any deactivation, at the low temperature of 320 °C. The influence of CeO₂ doping on the structure of the catalysts, the interactions between the mesoporous support and nickel species, and the reduction behaviors of Ni²⁺ ions were investigated in detail. In this work, the addition of CeO₂ to the composites increased the oxygen vacancies and active metallic nickel sites, and also decreased the size of the nickel particles, thus improving the low temperature catalytic activity and selectivity significantly.

The addition of CeO₂ to form Ni composite catalysts increased the oxygen vacancies and active metallic nickel sites thus improving the low temperature CO₂ methanation performance.     

Conversion of levulinic acid to γ-valerolactone over Ru/Al2O3–TiO2 catalyst under mild conditions

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water. In this study, mixed oxides Al₂O₃–TiO₂, Al₂O₃–MoO₃ and Al₂O₃–Co₃O₄ were synthesized by co-precipitation using aqueous solution of NaOH as precipitant. Ru catalysts supported on mixed oxides were prepared by impregnation method and their catalytic performances were tested in the hydrogenation of LA to GVL on a fixed bed reactor. The physicochemical properties of the catalysts were characterized by XRD, H₂-TPR, NH₃-TPD, and BET techniques. The TiO₂ component significantly affected the acidity of the catalyst, and thus its catalytic activity for the GVL yield was affected. The desired product GVL with a yield of about 97% was obtained over the Ru/Al₂O₃–TiO₂ catalyst under mild conditions (WHSV = 1.8 h⁻¹, T = 80 °C). Moreover, the catalyst Ru/Al₂O₃–TiO₂ exhibited excellent thermal stability in the test period of time.

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water.     

Improved electrical transport properties of polycrystalline La0.8(Ca0.12Sr0.08)MnO3 ceramics by Ag2O doping

Polycrystalline La_0.8(Ca_0.12Sr_0.08)MnO₃:mol%Ag_x (LCSMO:Ag_x, x = 0, 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized by the sol–gel technique. Structural, electrical and magnetic properties of the LCSMO:Ag_x ceramics were investigated in detail. X-ray diffraction (XRD) data analyses revealed that all the samples were crystalized in the orthorhombic structure with space group of Pnma. With the increase in Ag doping (x), the grain sizes of the LCSMO:Ag_x samples increased and the amount of grain boundaries (GBs) decreased accordingly. At the same time, the Mn–O bond distance and the Mn–O–Mn bond angles changed correspondingly, leading to the slight increase in the lattice constants (a, b and c) and slight expansion of cell volume (V). For the LCSMO:Ag_x sample with x = 0.3, the optimal values of temperature coefficient of resistivity (TCR) and magnetoresistance (MR) reached 16.22% K⁻¹ (265.1 K) and 42.07% K⁻¹ (270.48 K), respectively. In addition, the fitting analysis of ρ–T curves showed that the experimental data were consistent with the theoretical calculation data. In the T < T_MI (metal-insulator transition temperature) region, the electrical conduction mechanism of LCSMO:Ag_x was clarified by electron-magnon, electron–electron and electron-phonon scattering. In the T > T_MI region, the resistivity data were interpreted by using the adiabatic small-polaron hopping model. Furthermore, in the entire temperature range, the phenomenological equation called the percolation model was used to explain the resistivity data and the phase-separation mechanism of ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases. All the obtained results indicated that the improvement in the electrical properties of the LCSMO:Ag_x samples was attributed to the doping of Ag, which changed the A-site (La, Ca and Sr ions) average ion radius, the Mn–O–Mn bond angles and the Mn–O bond distance. In addition, the grain size increased, which led to improvement in the Mn⁴⁺ ion concentration and the GBs connectivity in the LCSMO:Ag_x polycrystalline ceramics.

Polycrystalline La_0.8(Ca_0.12Sr_0.08)MnO₃:mol%Ag_x (LCSMO:Ag_x, x = 0, 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized by the sol–gel technique.     

Continuous selective deoxygenation of palm oil for renewable diesel production over Ni catalysts supported on Al2O3 and La2O3–Al2O3

The present study provides, for the first time in the literature, a comparative assessment of the catalytic performance of Ni catalysts supported on γ-Al₂O₃ and γ-Al₂O₃ modified with La₂O₃, in a continuous flow trickle bed reactor, for the selective deoxygenation of palm oil. The catalysts were prepared via the wet impregnation method and were characterized, after calcination and/or reduction, by N₂ adsorption/desorption, XRD, NH₃-TPD, CO₂-TPD, H₂-TPR, H₂-TPD, XPS and TEM, and after the time-on-stream tests, by TGA, TPO, Raman and TEM. Catalytic experiments were performed between 300–400 °C, at a constant pressure (30 bar) and different LHSV (1.2–3.6 h⁻¹). The results show that the incorporation of La₂O₃ in the Al₂O₃ support increased the Ni surface atomic concentration (XPS), affected the nature and abundance of surface basicity (CO₂-TPD), and despite leading to a drop in surface acidity (NH₃-TPD), the Ni/LaAl catalyst presented a larger population of medium-strength acid sites. These characteristics helped promote the SDO process and prevented extended cracking and the formation of coke. Thus, higher triglyceride conversions and n-C₁₅ to n-C₁₈ hydrocarbon yields were achieved with the Ni/LaAl at lower reaction temperatures. Moreover, the Ni/LaAl catalyst was considerably more stable during 20 h of time-on-stream. Examination of the spent catalysts revealed that both carbon deposition and degree of graphitization of the surface coke, as well as, the extent of sintering were lower on the Ni/LaAl catalyst, explaining its excellent performance during time-on-stream.

Highly selective and stable Ni supported on La₂O₃–Al₂O₃ catalyst on the deCO/deCO₂ reaction paths for the production of renewable diesel.     

Effects of alternating current poling on the dielectric and piezoelectric properties of Pb(In0.5Nb0.5)O3–PbTiO3 crystals with a high Curie temperature

The alternating current poling (ACP) method has been become more and more popular recently because of its advantages of being low cost, time saving and highly efficient. Few ACP studies have focused on relaxor-PT crystals with a high coercive field and high Curie temperature or the effects of ACP on intrinsic and extrinsic contributions. The effects of the electric field, frequency, and number of cycles of ACP on the piezoelectric and dielectric properties of 〈001〉-oriented Pb(In_0.5Nb_0.5)O₃–PbTiO₃ ferroelectric crystals were studied. The dielectric permittivity ε₃₃^T/ε₀ and piezoelectric coefficient d₃₃ of an ACP sample are 3070 and 1400 pC N⁻¹, respectively, which are 14% and 18% larger than those of a DCP sample. Rayleigh analysis reveals that both intrinsic and extrinsic contributions are enhanced after ACP. The poling electric field, frequency and cycle number can influence the intrinsic and extrinsic contributions. The intrinsic contribution is significantly affected by the poling electric field, and cycle number, but it is not very sensitive to frequency, while the poling electric field, frequency and cycle number are very important for the extrinsic contribution. This work demonstrates that the uniform domain patterns are a critical factor for the enhancement of the piezoelectric properties.

The ε₃₃^T/ε₀ and d₃₃ values of ACP 0.66PIN–0.34PT crystals are shown to be 3070 and 1400 pC N⁻¹, respectively, which are 14% and 18% larger than those of a DCP sample, owing to the enhancement of both intrinsic and extrinsic contributions.     

Preparation and heat-insulating properties of Al2O3–ZrO2(Y2O3) hollow fibers derived from cogon using an orthogonal experimental design

Bionic design is efficient to develop high-performance lightweight refractories with sophisticated structures such as hollow ceramic fibers. Here, we report a four-stage procedure for the preparation of Al₂O₃–ZrO₂(Y₂O₃) hollow fibers using the template of cogon—a natural grass. Subsequently, to optimize the thermal performance of the fibers, four sets of preparation parameters, namely, x(Al₂O₃), solute mass ratio of the mixture, dry temperature, and sintering temperature were investigated. Through an orthogonal design, the optimal condition of each parameter was obtained as follows: x(Al₂O₃) was 0.70, solute mass ratio of the mixture was 15 wt%, dry temperature was 80 °C, and sintering temperature was 1100 °C. Overall, Al₂O₃–ZrO₂(Y₂O₃) hollow fibers show relatively low thermal conductivity (0.1038 W m⁻¹ K⁻¹ at 1000 °C), high porosity (95.0%), and low density (0.05–0.10 g cm⁻³). The multiphase compositions and morphology of Al₂O₃–ZrO₂(Y₂O₃) hollow fibers, which may contribute to their thermal properties, were also discussed.

Lightweight Al₂O₃–ZrO₂(Y₂O₃) hollow fibers with low thermal conductivity were prepared by a natural template—cogon grass.     

Microstructure,friction and corrosion resistance properties of a Ni–Co–Al2O3 composite coating

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy. The content of Al₂O₃ particles of the Ni–Co–Al₂O₃ composite coating prepared by electrophoresis–electrodeposition was significantly higher than the composite coating prepared by pulsed electrodeposition. The composite coating prepared by electrophoresis–electrodeposition exhibited a better anti-wear performance than that prepared by pulsed electrodeposition. The morphology, composition and microstructure of the composite coatings were determined by means of X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The hardness and friction properties of the samples were tested on the microhardness tester and the friction and wear loss tester respectively.

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy.