Structure,thermostability and magnetic properties of cubic Ce2−xTi2O7 pyrochlore obtained via sol–gel preparation

Lanthanum-based titanates have been attracting considerable interest by virtue of their structural operability and hence diverse physical properties. The preparation of lanthanum-based titanates with novel crystal structure is a fascinating task. In this work, we report the preparation of a cubic Ce_2−xTi₂O₇ pyrochlore using the sol–gel method. The crystal structure, thermostability and magnetism were studied via the temperature dependence of X-ray powder diffraction, X-ray photoelectron spectroscopy and magnetization measurements. It has been revealed that the as-prepared Ce_2−xTi₂O₇ pyrochlore possesses a cubic symmetry (space group: Fd$\bar{3}$m), however there is an 18(1)% vacancy of Ce ions in the as-prepared samples. No distinct phase transition and thermal expansion anomaly were observed in the investigated temperature range from 300 K to 700 K. Intriguingly, lattice defects may favor the transformation of Ce valence from +3 to +4 and an unusual weak magnetic ordering state emerged up to 400 K. The persistence of magnetism at such high temperatures is rare and mysterious for cerium titanates. Our findings provide the possibility of adjusting the crystal structure and magnetic properties of cerium titanates, anticipated to the development of lanthanum-based oxides.

We report a novel cubic Ce_2−xTi₂O₇ compound prepared via the sol–gel method. There is an 18% vacancy of Ce ions in the as-prepared samples. The lattice defects may favor the transformation of Ce valence from +4 to +3, and a weak magnetic ordering state emerges up to 400 K.     

Room temperature ferromagnetism in metallic Ti1−xVxO2 thin films

Transition metal doped TiO₂ diluted magnetic semiconductors have attracted considerable interest due to their room temperature ferromagnetism. However, most TiO₂ films are highly insulating, and thus the magnetic properties can not be controlled by tuning the carrier concentration. This will limit their application in controlling magnetization via electrical gating. Here, we deposit rutile Ti_1−xV_xO₂ (x = 0.03 and 0.05) films with the thickness between 30 and 245 nm by the pulsed laser deposition technique, and observe an obvious room temperature ferromagnetic behavior in all films. The high resolution X-ray photoelectron spectroscopy results indicate that V substituting Ti⁴⁺ ions in the TiO₂ lattice, with the +3 valence state having two unpaired d electrons, is responsible for the local spin. More importantly, the systemic investigations of transport properties for Ti_1−xV_xO₂ films reveal that the films are n-type and have metallic conductivity with a carrier density of about 10²⁰/cm³. Further studies suggest that the oxygen vacancies play a dual role of contributing to the metallic conductivity of the Ti_1−xV_xO₂ films, and also providing the free electrons to mediate the long-range ferromagnetic coupling between two magnetic polarons. These findings may offer promise for gate-tunable ferromagnetism in future semiconductor spintronics.

Transition metal doped TiO₂ diluted magnetic semiconductors have attracted considerable interest due to their room temperature ferromagnetism.     

Cold sintering of YBa2Cu3O7−δ

Cold sintering is a sintering technique which enables ceramic powders to be densified at greatly reduced temperatures compared to traditional solid state techniques, which often require temperatures in excess of 1000 °C. These temperatures often preclude the exploitation of size or orientational effects in ceramics as these are lost during heating. One such effect is the orientation of the crystallographic c axis in YBa₂Cu₃O_7−δ (YBCO) which can be controlled through applied pressure. This effect is of interest for increasing critical current density which is highly dependent on the orientation of the a–b (CuO₂) planes within the ceramic. Using cold sintering, we demonstrate that dense YBCO can be created at 180 °C (vs. 1000 °C using solid state) and demonstrate that the likely sintering mechanism is mediated by the cracking which occurs in YBCO when exposed to water. In addition, the ceramics produced show and retain the orientational effect, representing a unique opportunity to study the effect on critical current density. We show that the intergranular critical current when the a–b planes are parallel to the applied field is around 15% higher than when perpendicular.

Cold sintered superconducting YBa₂Cu₃O_7−δ densified at 180 °C shows enhanced critical current densities by exploiting grain alignment created during pressing.     

Influence of defect on the electrical and optical properties of A-site non-stoichiometry Ca0.67La0.22□0.11Ti(1−x)CrxO3−δ perovskite

An investigation of the dielectric dispersion, electrical properties, scaling behavior and optical defects of Ca_0.67La_0.22□_0.11Ti_(1−x)Cr_xO_3−δ (CLT_(1−x)Cr_x) with x = 0 and x = 0.1 compositions is presented. The square in the formula is attributed to a vacancy in A-site. Relaxation phenomena were studied with dielectric and modulus formalism, while, the conductivity mechanism was investigated using electrical conductivity. A high permittivity of around 10⁴, low dielectric loss and low electrical conductivity of around 10⁻³ S cm⁻¹ for Ca_0.67La_0.22TiO₃ (CLT) was observed. These values make this composition interesting for microelectric applications. A comparison between the Z′′ and M′′ indicated that the short-range carrier motion dominates at low temperature and becomes less localized at high temperature. The optical defects of CLT and Ca_0.67La_0.22Ti_0.9Cr_0.1O₃ (CLT_0.9Cr_0.1) were studied by electron paramagnetic resonance (EPR) spectroscopy. The results suggest the formation of a [TiO₆]⁹⁻ center, a (Ti³⁺–V_O) center, and dipole defect for CLT compound and Cr³⁺–V_O center defect for CLT_0.9Cr_0.1 compound. These defects are the source of the in-gap electron traps, which improve the optical properties of CLT_(1−x)Cr_x and hence make it an interesting optical material for different applications.

An investigation of the real part of permittivity for the compositions (a) x = 0 and (b) x = 0.1 solid solution Ca_0.67La_0.22□_0.11Ti_(1−x)Cr_xO_3−δ ceramics.     

Chemical solution deposition of Y1−xGdxBa2Cu3O7−δ–BaHfO3 nanocomposite films: combined influence of nanoparticles and rare-earth mixing on growth conditions and transport properties

Y_1−xGd_xBa₂Cu₃O_7−δ–BaHfO₃ (YGBCO–BHO) nanocomposite films containing 12 mol% BHO nanoparticles and different amounts of Gd were prepared by chemical solution deposition following the trifluoroacetic route on SrTiO₃ single crystals in order to study the influence of the rare earth stoichiometry on structure, morphology and superconducting properties of these films. We optimized the growth process for each of several Gd contents of the 220 nm thick YGBCO–BHO films by varying crystallization temperature and oxygen partial pressure. This optimization process led to the conclusion that mixing the rare earths in YGBCO–BHO films leads to wider growth parameter windows compared to YBCO-BHO and GdBCO-BHO films giving larger freedom for selecting the most convenient processing parameters in order to adapt to different substrates or applications which is very important for the industrial production of coated conductors. The optimized films show a continuous increase of T_c with Gd content x from ∼90 K for the YBCO-BHO films to ∼94 K for the GdBCO-BHO films. Consequently, an increase of the 77 K self-field J_c with Gd content is observed reaching values > 7 MA cm⁻² for Gd contents x > 0.5. The transport properties of these films under applied magnetic fields are significantly improved with respect to the pristine YBCO films. All YGBCO–BHO nanocomposite films grew epitaxially with c-axis orientation and excellent out-of-plane and in-plane texture. The films are dense with a low amount of pores and only superficial indentations.

Superconducting Y_1–xGd_xBa₂Cu₃O_7–δ–BaHfO₃ nanocomposite films were prepared by chemical solution deposition on SrTiO₃ substrates in order to study the influence of the rare earth stoichiometry on their structure, morphology and electrical properties.     

Colossal dielectric permittivity,reduced loss tangent and the microstructure of Ca1−xCdxCu3Ti4O12−2yF2y ceramics

Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y (x = y = 0, 0.10, and 0.15) ceramics were successfully prepared via a conventional solid-state reaction (SSR) method. A single-phase CaCu₃Ti₄O₁₂ with a unit cell ∼7.393 Å was detected in all of the studied ceramic samples. The grain sizes of sintered Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y ceramics were significantly enlarged with increasing dopant levels. Liquid-phase sintering mechanisms could be well matched to explain the enlarged grain size in the doped ceramics. Interestingly, preserved high dielectric permittivities, ∼36 279–38 947, and significantly reduced loss tangents, ∼0.024–0.033, were achieved in CdF₂ codoped CCTO ceramics. Density functional theory results disclosed that the Cu site is the most preferable location for the Cd dopant. Moreover, F atoms preferentially remained close to the Cd atoms in this structure. An enhanced grain boundary response might be a primary cause of the improved dielectric properties in Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y ceramics. The internal barrier layer capacitor model could well describe the colossal dielectric response of all studied sintered ceramics.

CdF₂ defect clusters result in enhancement of dielectric properties of the Ca_1−xCd_xCu₃Ti₄O_12−2yF_2y ceramics.     

Critical current density improvement in CSD-grown high-entropy REBa2Cu3O7−δ films

High-entropy oxide (HEO) superconductors have been developed since very recently. Different superconductors can be produced in the form of a high-entropy compound, including REBa₂Cu₃O_7−δ (REBCO). However, until now, mainly bulk samples (mostly in polycrystalline form) have been reported. In this work, the first CSD-grown high-entropy (HE) REBCO nanocomposite films were successfully synthesized. In particular, high-quality Gd_0.2Dy_0.2Y_0.2Ho_0.2Er_0.2Ba₂Cu₃O_7−δ nanocomposite films with 12 mol% BaHfO₃ nanoparticles were grown on SrTiO₃ substrates. The X-ray diffraction patterns show a near-perfect c-axis oriented grain growth. Both T_c and 77 K J^sf_c, 91.9 K and 3.5 MA cm⁻², respectively, are comparable with the values of the single-RE REBCO films. Moreover, at low temperatures, specifically at 30 K, the J_c values are larger than those of the single-RE samples. A transmission electron microscopy (TEM) study, including energy-dispersive X-ray spectroscopy (EDXS) measurements, reveals that the different RE³⁺ ions are distributed homogeneously in the matrix without forming clusters. This distribution causes point-like pinning centres that explain the superior performances of these samples at low temperatures. Although still seen as a proof-of-concept for the feasibility of preparing such films, these results demonstrate that the HE REBCO films are a promising option for the future fabrication of high-performance coated conductors. In the investigated B–T range, however, their J_c values are still lower than those of other, medium-entropy REBCO films, which shows that an optimization of the composition of the HE REBCO films is needed to maximize their performance.

High-resolution STEM-EDXS chemical analysis of (a) medium-entropy and (b) high-entropy REBCO films grown on SrTiO₃. The RE signals are homogeneously distributed in the films.     

Frequency and temperature-dependence of dielectric permittivity and electric modulus studies of the solid solution Ca0.85Er0.1Ti1−xCo4x/3O3 (0 ≤ x ≤ 0.1)

The dielectric properties of Ca_0.85Er_0.1Ti_1−xCo_4x/3O₃ (CETCo_x) (x = 0.00, 0.05 and 0.10), prepared by a sol–gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCo_x decreased sharply with increasing frequency. This is referred to as the Maxwell–Wagner type of polarization in accordance with Koop''s theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.

Frequency dependence of real (ε′) part of permittivity of CETCo_x for x = 0.00, 0.05 and 0.10 for T = 600 K.     

Recently synthesized (Ti1−xMox)2AlC (0 ≤ x ≤ 0.20) solid solutions: deciphering the structural,electronic, mechanical and thermodynamic properties via ab initio simulations

The structural, electronic, mechanical and thermodynamic properties of (Ti_1−xMo_x)₂AlC (0 ≤ x ≤ 0.20) were explored using density functional theory. The obtained lattice constants agree well with the experimental values. The electronic band structure confirms the metallic nature. Strengthening of covalent bonds due to Mo substitution is confirmed from the study of band structure, electronic density of states and charge density mapping. The elastic constants satisfy the mechanical stability criteria. Strengthening of covalent bonds leads to enhanced mechanical properties. (Ti_1−xMo_x)₂AlC compounds are found to exhibit brittle behavior. The anisotropic nature of (Ti_1−xMo_x)₂AlC is revealed from the direction dependent Young''s modulus, compressibility, shear modulus and Poisson''s ratio as well as the shear anisotropic constants and the universal anisotropic factor. The Debye temperature, minimum thermal conductivity, Grüneisen parameter and melting temperature of (Ti_1−xMo_x)₂AlC have been calculated for different Mo contents. Our calculated values are compared with reported values, where available.

The structural, electronic, mechanical and thermodynamic properties of (Ti_1−xMo_x)₂AlC (0 ≤ x ≤ 0.20) were explored using density functional theory.     

Gd3+ and Bi3+ co-substituted cubic zirconia; (Zr1−x−yGdxBiyO2−δ): a novel high κ relaxor dielectric and superior oxide-ion conductor

Solid oxide fuel cells (SOFCs) offer several advantages over lower temperature polymeric membrane fuels cells (PMFCs) due to their multiple fuel flexibility and requirement of low purity hydrogen. In order to decrease the operating temperature of SOFCs and to overcome the high operating cost and materials degradation challenges, the Cubic phase of ZrO₂ was stabilized with simultaneous substitution of Bi and Gd and the effect of co-doping on the oxide-ion conductivity of Zr_1−x−yBi_xGd_yO_2−δ was studied to develop a superior electrolyte separator for SOFCs. Up to 30% Gd and 20% Bi were simultaneously substituted in the cubic ZrO₂ lattice (Zr_1−x−yGd_xBi_yO_2−δ, x + y ≤ 0.4, x ≤ 0.3 and y ≤ 0.2) by employing a solution combustion method followed by multiple calcinations at 900 °C. Phase purity and composition of the material is confirmed by powder XRD and EDX measurements. The formation of an oxygen vacant Gd/Bi co-doped cubic zirconia lattice was also confirmed by Raman spectroscopy study. With the incorporation of Bi³⁺ and Gd³⁺ ions, the cubic Zr_1−x−yBi_xGd_yO_2−δ phase showed relaxor type high κ dielectric behaviour (ε′ = 9725 at 600 °C at applied frequency 20 kHz for Zr_0.6Bi_0.2Gd_0.2O_1.8) with T_m approaching 600 °C. The high polarizability of the Bi³⁺ ion coupled with synergistic interaction of Bi and Gd in the host ZrO₂ lattice seems to create the more labile oxide ion vacancies that enable superior oxide-ion transport resulting in high oxide ion conductivity (σ_o > 10⁻² S cm⁻¹, T > 500 °C for Zr_0.6Bi_0.2Gd_0.2O_1.8) at relatively lower temperatures.

The high polarizability of the Bi³⁺ ion coupled with synergistic interaction of Bi and Gd in the host ZrO₂ lattice seems to create the more labile oxide ion vacancies that enable high oxide ion conductivity at lower temperatures.     

Photocatalytic dye-degradation activity of nano-crystalline Ti1−xMxO2−δ (M =Ag,Pd, Fe,Ni and x = 0, 0.01) for water pollution abatement

Nanocrystalline metal-ion (M = Fe, Ni, Ag, and Pd) doped and undoped anatase-TiO₂ powders were prepared using a solution combustion method. The photocatalytic degradation of different dyes such as methylene blue (MB), rhodamine B (RB), rhodamine B base (RBB), and thionine acetate (TA) was investigated under UV exposure. The degradation rate of the dyes were found to be better in the case of Ag⁺ and Pd²⁺ doped TiO₂, whereas Fe³⁺ and Ni²⁺ doped TiO₂ showed lower photocatalytic activity compared to undoped TiO₂ nanoparticles. Combustion synthesized catalysts exhibited much better activity compared to the commercial Degussa P25 (75% anatase + 25% rutile) TiO₂ photocatalyst. The intermediate states created in the band gap of the TiO₂ photocatalyst due to doping of first row transition metal ions (such as Fe³⁺ and Ni²⁺) into the TiO₂ lattice act as recombination centres and the electrons present in the d-orbital quench the photogenerated holes by indirect recombination, hence increasing e⁻–h⁺ recombination rates. As a result, a decrease in the photocatalytic activity of TiO₂ doped with first row transition metal ions is observed. However, in the case of noble metal ions (such as Ag⁺ and Pd²⁺) in TiO₂, photoreduction of Ag⁺ and Pd²⁺ ions occurs upon UV irradiation, hence the noble metal-ions act as electron scavengers. Consequently, the lifetime of the holes (h⁺) increases and hence higher photocatalytic oxidation activity of the dyes is observed. A novel strategy of electron scavenging is envisaged here to develop Ag⁺ and Pd²⁺ doped TiO₂ to increase the photocatalytic oxidation of organic dyes for the development of better water pollution abatement catalysts. Redox-pair stabilization in the TiO₂ lattice similar to photo-chromic glasses play a defining role in enhancing the photocatalytic activity of the catalyst and is a key finding for the development of superior photocatalysts. With the help of UV-vis and fluorescence spectroscopy, the mechanisms of the superior oxidation activity of Pd²⁺ and Ag⁺ doped TiO₂ nanoparticles are explained.

Redox-pair stabilization in TiO₂ lattice by doping of Ag⁺ and Pd²⁺ ions play a defining role in enhancing the photocatalytic activity of the catalyst by scavenging electrons generated through UV-irradiation on the catalyst.     

Electronic structure of iron dinitrogen complex [(TPB)FeN2]2−/1−/0: correlation to Mössbauer parameters

Low-valent species of iron are key intermediates in many important biological processes such as the nitrogenase enzymatic catalytic reaction. These species play a major role in activating highly stable N₂ molecules. Thus, there is a clear need to establish the factors which are responsible for the reactivity of the metal–dinitrogen moiety. In this regard, we have investigated the electronic structure of low-valent iron (2−/1−/0) in a [(TPB)FeN₂]^2−/1−/0 complex using density functional theory (DFT). The variation in the oxidation states of iron in the nitrogenase enzyme cycle is associated with the flexibility of Fe→B bonding. Therefore, the flexibility of Fe→B bonding acts as an electron source that sustains the formation of various oxidation states, which is necessary for the key species in dinitrogen activation. AIM calculations are also performed to understand the strength of Fe→B and Fe–N₂ bonds. A detailed interpretation of the contributions to the isomer shift (IS) and quadrupole splitting (ΔE_Q) are discussed. The major contribution to IS comes mainly from the 3s-contribution, which differs depending on the d orbital population due to different shielding. The valence shell contribution also comes from the 4s-orbital. The Fe–N₂ bond distance has a great influence on the Mössbauer parameters, which are associated with the radial distribution, i.e. the shape of the 4s-orbital and the charge density at the nucleus. A linear relationship between IS with Fe–N₂ and ΔE_Q with Fe–N₂ is observed.

We use density functional theory studies to explore the electronic structure, bonding and spectroscopic analysis of a low-valent iron (2−/1−/0) complex [(TPB)FeN₂]^2−/1−/0 and reveled the factor which affects the reactivity of the metal–dinitrogen moiety.     

Lymphotoxin β receptor signaling promotes tertiary lymphoid organogenesis in the aorta adventitia of aged ApoE−/− mice

Atherosclerosis involves a macrophage-rich inflammation in the aortic intima. It is increasingly recognized that this intimal inflammation is paralleled over time by a distinct inflammatory reaction in adjacent adventitia. Though cross talk between the coordinated inflammatory foci in the intima and the adventitia seems implicit, the mechanism(s) underlying their communication is unclear. Here, using detailed imaging analysis, microarray analyses, laser-capture microdissection, adoptive lymphocyte transfers, and functional blocking studies, we undertook to identify this mechanism. We show that in aged apoE^−/− mice, medial smooth muscle cells (SMCs) beneath intimal plaques in abdominal aortae become activated through lymphotoxin β receptor (LTβR) to express the lymphorganogenic chemokines CXCL13 and CCL21. These signals in turn trigger the development of elaborate bona fide adventitial aortic tertiary lymphoid organs (ATLOs) containing functional conduit meshworks, germinal centers within B cell follicles, clusters of plasma cells, high endothelial venules (HEVs) in T cell areas, and a high proportion of T regulatory cells. Treatment of apoE^−/− mice with LTβR-Ig to interrupt LTβR signaling in SMCs strongly reduced HEV abundance, CXCL13, and CCL21 expression, and disrupted the structure and maintenance of ATLOs. Thus, the LTβR pathway has a major role in shaping the immunological characteristics and overall integrity of the arterial wall.     

Up-conversion white emission and other luminescence properties of a YAG:Yb2O3·Tm2O3·Ho2O3@SiO2 glass-nanocomposite

We report on a glass-nanocomposite material consisting of yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) nanocrystals co-doped with Yb³⁺, Tm³⁺ and Ho³⁺ ions as well as entrapped into a SiO₂ xerogel. This 94YAG·5Yb₂O₃·0.8Tm₂O₃·0.2Ho₂O₃@SiO₂ (abbr. YAG:YbTmHo@SiO₂) nanocomposite material has been prepared by sol–gel procedure. Its structure and morphology has been characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques as well as energy dispersive X-ray (EDX), X-ray photoelectron (XPS) and luminescence spectroscopies. The luminescent glass-nanocomposite exhibited an up-conversion effect under λ_exc = 980 nm and emission when excited under 355 nm in steady-state conditions. Then time-resolved luminescence emission was observed, when the sample was excited at 290 and 355 nm by a pulse laser. Average decay times for the SiO₂ matrix and for some transitions of the Tm³⁺ and Ho³⁺ dopants present in the YAG:YbTmHo@SiO₂ material have been evaluated. The luminescent nanocomposite when excited under 290 or 355 nm wavelengths in both conditions emits blue light. However, the nanocomposite is promising as a single-source white-light phosphor owing to its up-conversion luminescence under 980 nm excitation. Such optical features make the studied material an alternative phosphor.

We present a glass-nanocomposite of the type YAG:YB³⁺, Tm³⁺, Ho³⁺@SiO₂ as an alternative white phosphor based on up-conversion effect.     

In-plasma-catalysis for NOx degradation by Ti3+ self-doped TiO2−x/γ-Al2O3 catalyst and nonthermal plasma

In an attempt to realize the efficient treatment of NO_x, a mixed catalyst of Ti³⁺ self-doped TiO_2−x and γ-Al₂O₃ was constructed by reducing commercial TiO₂. The degradation effect on NO_x was evaluated by introducing the mixed catalyst into a coaxial dual-dielectric barrier reactor. It was found that the synthesized TiO_2−x could achieve considerable degradation effects (84.84%, SIE = 401.27 J L⁻¹) in a plasma catalytic system under oxygen-rich conditions, which were better than those of TiO₂ (73.99%) or a single plasma degradation process (26.00%). The presence of Ti³⁺ and oxygen vacancies in TiO_2−x resulted in a relatively narrow band gap, which contributed to catalyzing deeply the oxidation of NO_x to NO₂⁻ and NO₃⁻ during the plasma-induced “pseudo-photocatalysis” process. Meanwhile, the TiO_2−x showed an improved discharge current and promoted discharge efficiency, explaining its significant activation effect in the reaction. Reduced TiO_2−x could achieve an impressive degradation effect in a long-time plasma-catalysis process, and still maintained its intrinsic crystal structure and morphology. This work provides a facile synthesis procedure for preparing Ti³⁺ self-doped TiO_2−x with practical and scalable production potential; moreover, the novel combination with plasma also provides new insights into the low-temperature degradation of NO_x.

TiO_2−x has a smaller forbidden band width, more abundant Ti³⁺ and oxygen vacancies, so as to obtain a better and more stable degradation effect of NO_x in plasma-catalysis process.     

Characterization of electrodeposited undoped and doped thin ZnO passive films on zinc metal in alkaline HCO3−/CO32− buffer solution

Electrochemical characterization of anodically grown thin ZnO films on pure zinc metal was studied in pH 9.2 bicarbonate/carbonate buffer solution. The different undoped passive films were formed potentiostatically in pH 9.2 borate buffer solution at processing anodic voltage (V_a) of −1.04, −1.02, −1.0 and −0.99 V (vs. Ag/AgCl). While, various doped ZnO films were fabricated by anodizing the metal at a fixed potential of −1.00 V in the same borate buffer solution containing different amounts of LiCl or InCl₃. The electrochemical and semiconducting properties of all formed films were investigated using chronoamperometric measurements, EIS and Mott–Schottky analysis supported by scanning electron microscopy. The impedance results showed a direct correlation between V_a and the value of either total resistance (R_f) of undoped passive film or its thickness (δ_f). It is evident that anodization can afford better conditions for forming thicker compact passive films with more advanced barrier properties. On the other hand, R_f decreases with increasing Li-doping level in the oxide film, and increases in case of In-doping. Interestingly, R_f values of the doped films are always lower when compared to its value for the undoped film grown at −1.00 V, likely due to possible change in the film microstructure upon doping. For both undoped and doped ZnO films, Mott–Schottky plots reveals unintentional n-type conductivity with high electron density. Moreover, with increasing dopant level in ZnO host materials, Mott–Schottky analysis revealed a parallel correlation between charge carrier donor concentration (N_D) and the passive film thickness (δ_f), where the trend of their values are to decrease for Li⁺-doped and to increase for In³⁺-doped films.

The trend of charge carrier density (N_D) and film thickness (δ_f) dependence on the parameter is indicated on each arrow for undoped, Li-doped, and In-doped ZnO semiconductor materials.     

A mitochondrion-targeted dual-site fluorescent probe for the discriminative detection of SO32− and HSO3− in living HepG-2 cells

Sulfur dioxide, known as an environmental pollutant, produced during industrial productions is also a common food additive that is permitted worldwide. In living organisms, sulfur dioxide forms hydrates of sulfite (SO₂·H₂O), bisulfite (HSO₃⁻) and sulfite (SO₃²⁻) under physiological pH conditions; these three exist in a dynamic balance and play a role in maintaining redox balance, further participating in a wide range of physiological and pathological processes. On the basis of the differences in nucleophilicity between SO₃²⁻ and HSO₃⁻, for the first time, we built a mitochondrion-targeted dual-site fluorescent probe (Mito-CDTH-CHO) based on benzopyran for the highly specific detection of SO₃²⁻ and HSO₃⁻ with two diverse emission channels. Mito-CDTH-CHO can discriminatively respond to the levels of HSO₃⁻ and SO₃²⁻. Besides, its advantages of low cytotoxicity, superior biocompatibility and excellent mitochondrial enrichment ability contribute to the detection and observation of the distribution of sulfur dioxide derivatives in living organisms as well as allowing further studies on the physiological functions of sulfur dioxide.

Rational design and sensing mechanism of a dual-site fluorescence probe for HSO₃⁻ and SO₃²⁻.     

Bridging and synergistic effect of the pyrochlore like Bi2Zr2O7 structure with robust CdCuS solid solution for durable photocatalytic removal of the organic pollutants

Herein, a strong redox ability photocatalyst of CdCuS solid solution composited with pyrochlore like Bi₂Zr₂O₇ has been fabricated by the simple hydrothermal method. The robust CdCuS solid solution materials perform the supporting role to the Bi₂Zr₂O₇ nano materials. The structural, optical, valence and vibrational states of the prepared heterostructure materials were analyzed using various characterization techniques. The photocatalytic activity of the as-synthesized Bi₂Zr₂O₇/CdCuS heterostructure has been verified under direct solar light and ambient conditions. The synthesized Bi₂Zr₂O₇/CdCuS nano combination exhibits a better photocatalytic activity for the removal of methylene blue and 4-nitrophenol organic probe molecules. The heterostructure formation between the samples is confirmed by HRTEM analysis. The improved rate of the photocatalytic reaction of the samples is attributed to the formation of heterostructures at the interface. The close interfacial contact between the two materials discloses the effective charge transfer, which leads to suppressed charge carrier recombination. The enhanced photo catalytic activity of redox-mediator-free-Bi₂Zr₂O₇/CdCuS heterostructure, possibly will be credited to the robust redox ability and the several charge transfer channels in the tight contact. The chief radicals produced in the catalytic reduction reaction have been predicted by the scavenger trapping methods and the results are discussed in detail. The obtained information from this study on Bi₂Zr₂O₇/CdCuS delivers some new visions for the design of active photocatalysts with multiple benefits.

Photocatalytic degradation mechanism for CdCuS solid solution supported pyrochlore like Bi₂Zr₂O₇.     

Color-tunable photoluminescence and energy transfer of (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ solid solutions for white light emitting diodes

(Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ solid solution phosphors were synthesized by introducing the isostructural Mn₃Al₂(SiO₄)₃ (MAS) into Tb₃Al₅O₁₂:Ce³⁺ (TbAG). Under 456 nm excitation, (Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ shows energy transfers (ET) in the host, which can be obtained from the red emission components to enhance color rendering. Moreover, (Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ (x = 0–0.2) exhibits substantial spectral broadening (68 → 86 nm) due to the 5d → 4f transition of Ce³⁺ and the ⁴T₁ → ⁶A₁ transition of Mn²⁺. The efficiency of energy transfer (η_T, Ce³⁺ → Mn²⁺) gradually increases with increasing Mn²⁺ content, and the value reach approximately 32% at x = 0.2. Namely, the different characteristics of luminescence evolution based on the effect of structural variation by substituting the (MnSi)⁶⁺ pair for the larger (TbAl)⁶⁺ pair. Therefore, with structural evolution, the luminescence of the solid solution phosphors could be tuned from yellow to orange-red, tunable by increasing the content of MAS for the applications of white light emitting diodes (wLED).

(Tb_1−xMn_x)₃Al₂(Al_1−xSi_x)₃O₁₂:Ce³⁺ solid solution phosphors were synthesized by introducing the isostructural Mn₃Al₂(SiO₄)₃ (MAS) into Tb₃Al₅O₁₂:Ce³⁺ (TbAG).