Cu2−xSe nanoparticles (Cu2−xSe NPs) mediated neurotoxicity via oxidative stress damage in PC-12 cells and BALB/c mice

Cu_2−xSe nanoparticles (Cu_2−xSe NPs) are widely used for optical diagnostic imaging and photothermal therapy due to their strong near-infrared (NIR) optical absorption. With the continuous expansion of applications using Cu_2−xSe NPs, their biosafety has received increasing attention in recent years. Cu_2−xSe NPs can enter the brain by crossing the blood–brain barrier, but the neurotoxicity of NPs remains unclear. The present investigation provides direct evidence that the toxicity of Cu_2−xSe NPs can be specifically exploited to kill rat pheochromocytoma PC-12 cells (a cell line used as an in vitro model for brain neuron research) in dose- and time-dependent manners. These cytotoxicity events were accompanied by mitochondrial damage, adenosine triphosphate (ATP) depletion, production of oxidizing species (including reactive oxygen species (ROS), malondialdehyde (MDA) and hydrogen peroxide (H₂O₂)), as well as reductions in antioxidant defense systems (glutathione (GSH) and superoxide dismutase (SOD)). Moreover, our in vivo study also confirmed that Cu_2−xSe NPs markedly induced neurotoxicity and oxidative stress damage in the striatum and hippocampal tissues of BALB/c mice. These findings suggest that Cu_2−xSe NPs induce neurotoxicity in PC-12 cells and BALB/c mice via oxidative stress damage, which provides useful information for understanding the neurotoxicity of Cu_2−xSe NPs.

Cu_2−xSe nanoparticles (Cu_2−xSe NPs) are widely used for optical diagnostic imaging and photothermal therapy due to their strong near-infrared (NIR) optical absorption.     

Intrinsic structural distortion and exchange interactions in SmFexCr1−xO3 compounds

The effect of substituting different amounts of magnetic metal Fe on the magnetic properties of SmFe_xCr_1−xO₃ (0 < x < 0.5) is reported here in order to probe the relation between the structural distortion and magnetism in these materials. The structural properties of the samples were characterized using X-ray diffraction with Rietveld refinements, and Raman spectroscopy carried out at ambient temperature. Magnetization data reveals the Neel temperature (T_N, where the Cr(Fe) ions order) increases with an increase in the average B-site ionic radius, and average Cr(Fe)–O–Cr(Fe) bond angle. By fitting the temperature dependence of the magnetic susceptibility to the Curie–Weiss law modified by the Dzyaloshinskii–Moriya (DM) interaction, the strengths of the symmetric and antisymmetric Cr(Fe)–Cr(Fe) exchange interactions (J and D) were determined. It was found that the strength of the symmetric interaction J (reflected in the changes in the Neel temperature) increases with the replacement of Cr³⁺ with Fe³⁺, which is ascribed to the changes in the average Cr(Fe)–O–Cr(Fe) bond angle and bond lengths. Meanwhile, the antisymmetric interaction D a slightly decreases, which may be ascribed to the displacement of oxygen ions (dO) away from their “original” middle point.

The relationship between intrinsic structural distortions and exchange interactions in SmFe_xCr_1−xO₃ compounds was studied.     

The photoelectron-imaging spectroscopic study and chemical bonding analysis of VO2−, NbO2− and TaO2−

The transition-metal di-oxides, namely VO₂⁻, NbO₂⁻ and TaO₂⁻ have been studied using photoelectron velocity map imaging (PE-VMI) in combination with theoretical calculations. The adiabatic electron affinities of VO₂⁻, NbO₂⁻ and TaO₂⁻ are confirmed to be 2.029(8), 1.901(10) and 2.415(8) eV, respectively. By combining Franck–Condon (FC) simulation with theoretical calculations, the vibrational feature related to Nb–O and Ta–O stretching modes for the ground state has been unveiled. The photoelectron angular distribution (PAD) for VO₂⁻, NbO₂⁻ and TaO₂⁻ is correlated to the photo-detachment of the highest occupied molecular orbitals (HOMOs), which primarily gets involved in s- and d-orbitals of the V, Nb and Ta atoms. A variety of theoretical calculations have been used to analyze the chemical bonding features of VO₂^−1/0, NbO₂^−1/0 and TaO₂^−1/0, which show that the strong M–O (M = V, Nb and Ta) bond is mainly characterized as ionicity.

The transition-metal di-oxides, namely VO₂⁻, NbO₂⁻ and TaO₂⁻ have been studied using photoelectron velocity map imaging (PE-VMI) in combination with theoretical calculations.     

NiO/NixCo3−xO4 porous ultrathin nanosheet/nanowire composite structures as high-performance supercapacitor electrodes

The demand for a new generation of high-safety, long-lifespan, and high-capacity power sources increases rapidly with the growth of energy consumption in the world. Here we report a facile method for preparing architecture materials made of NiO/Ni_xCo_3−xO₄ porous nanosheets coupled with NiO/Ni_xCo_3−xO₄ porous nanowires grown in situ on nickel foams using a hydrothermal method without any binder followed by a heat treatment process. The nanosheet-shaped NiO/Ni_xCo_3−xO₄ species in the nanosheet matrix function well as a scaffold and support for the dispersion of the Ni_xCo_3−xO₄ nanowires, resulting in a relatively loose and open structure within the electrode matrix. Among all composite electrodes prepared, the one annealed in air at 300 °C displays the best electrochemical behavior, achieving a specific capacitance of 270 mF cm⁻² at 5 mA cm⁻² while maintaining excellent stability (retaining ≈ 89% of the max capacitance after 20 000 cycles), demonstrating its potential for practical application in power storage devices.

Porous ultrathin nanosheet/nanowire composite structures are prepared as high-performance supercapacitor electrodes which exhibit excellent stability.     

Heterogeneous activation of persulfate by ZnCoxFe2−xO4 loaded on rice hull carbon for degrading bisphenol A

A new low-cost composite of ZnCo_xFe_2−xO₄ loaded on rice hull carbon (ZnCo_xFe_2−xO₄-RHC) was synthesized via waste ferrous sulfate (the industrial waste produced in the process of producing titanium dioxide) and rice hull as raw materials, which was applied for the degradation of bisphenol A (BPA) by heterogeneous activated peroxodisulfate (PS). A series of characterizations including XRD, SEM, FTIR, and BET analysis were carried out to analyze the structure and morphology of the materials. It is confirmed that the ZnCo_xFe_2−xO₄-RHC composites show better catalytic activity and performance than other control samples, which can be attributed to the synergistic effect of Fe and Co, ZnCo_xFe_2−xO₄ and RHC based on these analyses. The degradation rate of BPA by ZnCo_1.3Fe_0.7O₄-50%RHC reached 100% within 15 min, and it can still maintain good catalytic efficiency after 5 cycles. ESR test and XPS results showed that free radical and non-free radical processes were involved in BPA degradation. These findings offer a novel, low cost and simple strategy for rational design and modulation of catalysts for the industrial degradation of organic pollutants, and provide a new idea for the utilization of waste ferrous sulphate in titanium dioxide industry.

Mechanism of the activation on PS by ZnCo_1.3Fe_0.7O₄-RHC for the degradation of BPA.     

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.     

Chemical stability of Ca3Co4−xO9+δ/CaMnO3−δ p–n junction for oxide-based thermoelectric generators

An all-oxide thermoelectric generator for high-temperature operation depends on a low electrical resistance of the direct p–n junction. Ca₃Co_4−xO_9+δ and CaMnO_3−δ exhibit p-type and n-type electronic conductivity, respectively, and the interface between these compounds is the material system investigated here. The effect of heat treatment (at 900 °C for 10 h in air) on the phase and element distribution within this p–n junction was characterized using advanced transmission electron microscopy combined with X-ray diffraction. The heat treatment resulted in counter diffusion of Ca, Mn and Co cations across the junction, and subsequent formation of a Ca₃Co_1+yMn_1−yO₆ interlayer, in addition to precipitation of Co-oxide, and accompanying diffusion and redistribution of Ca across the junction. The Co/Mn ratio in Ca₃Co_1+yMn_1−yO₆ varies and is close to 1 (y = 0) at the Ca₃Co_1+yMn_1−yO₆–CaMnO_3−δ boundary. The existence of a wide homogeneity range of 0 ≤ y ≤ 1 for Ca₃Co_1+yMn_1−yO₆ is corroborated with density functional theory (DFT) calculations showing a small negative mixing energy in the whole range.

The heat treatment beneficially affects the performance of an all-oxide thermoelectric generator through phase and element distribution within this p–n junction.     

Efficient (Cu1−xAgx)2ZnSn(S,Se)4 solar cells on flexible Mo foils

Cation substitution plays a crucial role in improving the efficiency of Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. In this work, we report a significant efficiency enhancement of flexible CZTSSe solar cells on Mo foils by partial substitution of Cu⁺ with Ag⁺. It is found that the band gap (E_g) of (Cu_1−xAg_x)₂ZnSn(S,Se)₄ (CAZTSSe) thin films can be adjusted by doping with Ag with x from 0 to 6%, and the minimum E_g is achieved with x = 5%. We also found that Ag doping can obviously increase the average grain size of the CAZTSSe absorber from 0.4 to 1.1 μm. Additionally, the depletion width (W_d) at the heterojunction interface of CAZTSSe/CdS is found to be improved. As a result, the open-circuit voltage deficit (V_oc,def) is gradually decreased, and the band tailing is suppressed. Benefiting from the enhanced open-circuit voltage (V_oc), the power conversion efficiency (PCE) is successfully enhanced from 4.34% (x = 0) to 6.24% (x = 4%), and the V_oc,def decreases from 915 to 848 mV.

Cation substitution plays a crucial role in improving the efficiency of Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells.     

Investigation of crystal field effects for the spectral broadening of Yb3+-doped LuxY2−xO3 sesquioxide crystals

The investigation of crystal field effects is significant for elucidating the spectral characteristics of Yb³⁺-doped sesquioxide crystals for ultrafast laser generation. The narrow spectra of Yb³⁺-doped single sesquioxide crystals limit the generation of ultrafast lasers; in this study, the Y³⁺ ions were introduced into Lu₂O₃ single crystals by the employment of ion replacement to broaden the spectra. To analyze the spectral broadening, the responsible crystal field parameters (CFPs) were calculated. The conversion of the host dominant ion and the distortion of the ligand affected the values and signs of the CFPs, and further determined the energy level splitting and fluorescence spectra. A linear relationship expressed by the semi-empirical equations for Yb³⁺-doped sesquioxide crystals was produced, which could be used for high throughput spectral prediction. Opposite variations of high- and low-frequency vibrational energies and the influence of the electron–phonon coupling on the spectra were also achieved. The redshift from the crystal field and the blueshift from the electron–phonon coupling make the optimal spectral broadening appear when x = 1.19 in the Yb:Lu_xY_2−xO₃ crystals. The results of these analyses could provide some key clues for the development of Yb³⁺-doped crystals for the generation and amplification of ultrafast lasers.

A linear relationship connecting the properties of composition and spectrum was deduced in Yb³⁺-doped sesquioxide crystals, and the emission spectra of Yb:Lu_xY_2−xO₃ crystals broadened under the effects of crystal field and electron–phonon coupling.     

From spent alkaline batteries to ZnxMn3−xO4 by a hydrometallurgical route: synthesis and characterization

A series of Zn/Mn binary oxides with different molar ratios (1.4–11) were synthesized via co-precipitation from a solution obtained through the acidic (HCl) leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn–C batteries. The oxides obtained were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Magnetic properties of the samples were also investigated. The Raman spectroscopy results showed all the binary metallic oxides belong to the Zn_xMn_3−xO₄ (0.25 ≤ x ≥ 1.75) type. All showed a spinel crystalline structure. The saturation magnetization decreases with the Zn/Mn molar ratio; a maximum of 13.19 emu g⁻¹ was found for the molar ratio of 11 at the Curie temperature (25.5 K). XPS showed that all the synthesized compounds contained Mn²⁺, Mn³⁺ and Mn⁴⁺. Mn²⁺ was the most prominent at a molar ratio of 11, Mn³⁺ was most common at a molar ratio of 2, and Mn⁴⁺ at 1.4.

A series of Zn/Mn binary oxides with different molar ratios were synthesized via co-precipitation from a solution obtained through the leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn–C batteries.     

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.     

Barrier thickness dependence of MgxZn1−xO/ZnO quantum well (QW) on the performance of a p-NiO/QW/n-ZnO photodiode

An Mg_xZn_1−xO/ZnO quantum well (QW) structure, with various barrier (Mg_xZn_1−xO layer) thicknesses, was inserted into p-NiO/n-ZnO heterojunction photodiodes (HPDs) by using a radio-frequency magnetron sputtering system. The effect of various barrier thicknesses on the performance of QW-PDs was investigated. A band diagram shows that the QW-PD with 10 nm barrier layer presents a tunneling carrier transport mechanism, the UV- and visible-generated carriers tunnel through the thin barrier layer. Whereas the QW-PDs with thicker (≧25 nm) barrier layers show recombination-tunneling carrier transport. The visible-generated carriers are effectively confined within the well layer in the QW structure, causing the visible-response to be greatly reduced by more than 3 orders compared to that in the QW-PD with a 10 nm barrier layer. However, on further increasing the barrier thickness beyond 25 nm, the visible-response will no longer be reduced. In contrast, with decreasing the barrier thickness from 60 to 25 nm, the UV-response increases due to the overlap increase of the fundamental electron and hole wave function in the quantum well. Such a result drastically enhances the rejection ratio (320 nm/500 nm) from 264 for QW-PDs with a 10 nm barrier to 2986 for QW-PDs with a 25 nm barrier layer by a 11.3 ratio.

An Mg_xZn_1−xO/ZnO quantum well (QW) structure, with various barrier (Mg_xZn_1−xO layer) thicknesses, was inserted into p-NiO/n-ZnO heterojunction photodiodes (HPDs) by using a radio-frequency magnetron sputtering system.     

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⁻.     

The use of S2O82− and H2O2 as novel specific masking agents for highly selective “turn-on” fluorescent switching recognition of CN− and I− based on Hg2+–graphene quantum dots

In this study, we report that both CN⁻ and I⁻ can enhance the fluorescent intensity of Hg²⁺–graphene quantum dots (Hg²⁺–GQDs). However, the selectivity of the sensor was poor. Accordingly, simple specific masking agents can be directly used to solve this problem. Here, for the first time, we report the use of persulfate ion (S₂O₈²⁻) as a turn-on fluorescent probe of Hg²⁺–GQDs for selective CN⁻ detection, while hydrogen peroxide (H₂O₂) was selected for its sensing ability towards I⁻ ion detection. Interestingly, the signal was immediately measured after addition of the masking agent to Hg²⁺–GQDs and the sample because its interaction was very fast and efficient. The method had a linear response in the concentration ranges of 0.5–8 μM (R² = 0.9994) and 1–12 μM (R² = 0.9998) with detection limits of 0.17 and 0.20 μM for CN⁻ and I⁻, respectively. The sensor was successfully used for the dual detection of both CN⁻ and I⁻ in real water samples with satisfactory results. In conclusion, the specific masking agents in a Hg²⁺–GQDs system appeared to be good candidates for fluorometric “turn-on” sensors for CN⁻ and I⁻ with excellent selectivity over other ions.

In this study, we report that both CN⁻ and I⁻ can enhance the fluorescent intensity of Hg²⁺–graphene quantum dots (Hg²⁺–GQDs).     

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.     

Anchoring carbon layers and oxygen vacancies endow WO3−x/C electrode with high specific capacity and rate performance for supercapacitors

Herein, novel hierarchical carbon layer-anchored WO_3−x/C ultra-long nanowires were developed via a facile solvent-thermal treatment and a subsequent rapid carbonization process. The inner anchored carbon layers and abundant oxygen vacancies endowed the WO_3−x/C nanowire electrode with high conductivity, as measured with a single nanowire, which greatly enhanced the redox reaction active sites and rate performance. Surprisingly, the WO_3−x/C electrode exhibited outstanding specific capacitance of 1032.16 F g⁻¹ at the current density of 1 A g⁻¹ in a 2 M H₂SO₄ electrolyte and maintained the specific capacitance of 660 F g⁻¹ when the current density increased to 50 A g⁻¹. Significantly, the constructed WO_3−x/C//WO_3−x/C symmetric supercapacitors achieved specific capacitance of 243.84 F g⁻¹ at the current density of 0.5 A g⁻¹ and maintained the capacitance retention of 94.29% after 5000 charging/discharging cycles at the current density of 4 A g⁻¹. These excellent electrochemical performances resulted from the fascinating structure of the WO_3−x/C nanowires, showing a great potential for future energy storage applications.

A high-performance supercapacitor electrode comprising hierarchical carbon layer-anchored WO_3−x/C nanowires with inner abundant redox reaction active sites and numerous oxygen vacancies is presented.     

Study on the performance of NiO/ZnxZr1−x catalysts for CO2 hydrogenation

The NiO/Zn_xZr_1−x (x represents the molar mass of Zn) catalyst was prepared by the impregnation method and tested in CO₂ methanation. The activity results show that NiO/Zn_0.3Zr_0.7 has a higher CO₂ conversion rate and methane selectivity than NiO/ZnO and NiO/ZnO–ZrO₂. Combined with N₂ adsorption–desorption, H₂-TPR, CO₂-TPD, H₂-TPD, XRD, TEM, XPS and FTIR and other characterization methods, the physical and chemical properties of NiO/ZnO–ZrO₂ were studied. The incorporation of ZnO into NiO/ZrO₂ forms a ZnO–ZrO₂ solid solution, and the combination of the solid solution weakens the interaction between NiO and the oxide support, thereby promoting the reduction and dispersion of NiO. The H₂-TPR experiment results show that, because ZnO–ZrO₂ forms a solid solution, NiO is better dispersed on the surface, resulting in a significant reduction in the reduction temperature of NiO. Using FTIR to conduct CO₂ adsorption and methanation experiments on NiO/Zn_xZr_1−x to determine the adsorbed species and intermediates, the results show that CO₂ methanation follows the formate pathway.

The NiO/Zn_xZr_1−x (x represents the molar mass of Zn) catalyst was prepared by the impregnation method and tested in CO₂ methanation.     

MoO3−x-deposited TiO2 nanotubes for stable and high-capacitance supercapacitor electrodes

Here we report the supercapacitive properties of a novel MoO_3−x/TiO₂ nanotube composite prepared by a facile galvanostatic deposition technique and subsequently thermal treatment in an argon atmosphere between 350 °C and 550 °C. X-ray diffraction and X-ray photoelectron spectroscopy confirm the existence of MoO_3−x. The MoO_3−x/TiO₂ electrode prepared at 550 °C exhibits a high specific capacitance of 23.69 mF cm⁻² at a scan rate of 10 mV s⁻¹ and good cycling stability with capacitance retention of 86.6% after 1000 cycles in 1 M Na₂SO₄ aqueous solution. Our study reveals a feasible method for the fabrication of TiO₂ nanotubes modified with electroactive MoO_3−x as high-performance electrode materials for supercapacitors.

Here we report the supercapacitive properties of a novel MoO_3−x/TiO₂ nanotube composite prepared by a facile galvanostatic deposition technique and subsequently thermal treatment in an argon atmosphere between 350 °C and 550 °C.     

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.     

Influence of structure phase transition on the thermoelectric properties of Cu2Se1−xTex liquid-like compounds

Copper chalcogenide Cu₂(Se,Te) compounds are well known as typical p-type thermoelectric materials with a figure of merit (ZT) that can be optimized by the ratio of Se : Te. Here, by using the mechanical alloying and solid-state reaction methods, Te was substituted into Se sites within Cu₂Se as the formula Cu₂Se_1−xTe_x (x = 0.1, 0.2, 0.25, and 0.3). The observed changes in structural phase, grain morphologies, and grain size were recorded by XRD and FE-SEM imaging with the appearance of the secondary phase of Cu₂Te, with a Te content of x = 0.25. The layered structure morphology was observed more clearly at the high Te content. The electrical conductivity was greatly increased with enriched Te content while the maximum Seebeck coefficient was obtained in the Cu₂Se_0.75Te_0.25 sample. Accordingly, a power factor value of up to 9.84 μW cm⁻¹ K⁻² at 773 K was achieved. The appearance of a Cu₂Te phase with a Te content of 0.25 created a structural phase transition which results in a ZT value of 1.35 at 773 K in the Cu₂Se_0.75Te_0.25 sample.

Copper chalcogenide Cu₂(Se,Te) compounds are well known as typical p-type thermoelectric materials with a figure of merit (ZT) that can be optimized by the ratio of Se : Te.