Oxygen Vacancies In Lattice Research Articles

Mechanistic insight into high response of carbon monoxide gas sensor developed by nickel manganate nanorod decorated reduced graphene oxide

Nickel manganate nanorod (NNM) decorated reduced graphene oxide (NNMG) was developed and its structure-property correlations in light of X-ray diffraction (XRD), Raman, field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) were evaluated. The starring role of NNM and reduced graphene oxide (RGO) in NNMG for CO sensing was explored and an insight into the mechanistic pathway of sensing was proposed. NNMG displayed an excellent response % (∼ 7000) and sensitivity (0.60 ppm−1), which can surpass most stable efficient sensors, indicative of the synergistic effect of RGO and NNM. Moreover, NNMG can competently sense CO gas at wide range of concentration (25–200 ppm) with good stability and reversibility. Ligand like approach of CO facilitated donation of electron to the lattice oxygen vacancy and subsequently decrease electron barrier at the Schottky junction, resulting the higher response. The obtained outcomes demonstrated that the rational design of nanorod decorated RGO could be a promising strategy to improve CO sensing performance.

Doping of Chlorine from a Neoprene Adhesive Enhances Degradation Efficiency of Dyes by Structured TiO2-Coated Photocatalytic Fabrics

We demonstrate that using neoprene as a binder during the fabrication of TiO2-coated fabrics enhances the rates of photodegradation of dyes by the fabrics. The neoprene binder simultaneously modifies the surface of the TiO2 particles with Cl and dopes the TiO2 with Cl, without requiring high temperatures or other harsh laboratory treatments. The adsorption of chlorine on the surface and doping of the lattice with chlorine were confirmed by X-ray photoelectron spectroscopy. The chloride ions adsorbed onto the TiO2 surface introduces a negative surface charge that enhances electrostatic adsorption of cationic dyes, and greatly improves the self-sensitizing degradation performance of the dyes. Chloride ions replace lattice oxygen atoms in TiO2, inducing lattice oxygen vacancies, that reduce the apparent band gap of the TiO2 particles, enhancing its absorption of visible light, and further increasing the photocatalytic activity of the composite-coated fabric. The degradation rates of RhB and MB over 50 min were 95.2% and 96.0%, respectively. The degradation rate for MO reached 95.4% after 180 min. We also show that •OH and •O2− are active agents in the dye-degradation mechanism. Moreover, the photocatalytic performance of the composite-coated fabric was unchanged after eight cycles of photocatalytic degradation of RhB, demonstrating that the photocatalyst-coated fabrics was highly recyclable.

Preparation of Ba2FeNbO6 double perovskite ceramics from molten-salt synthesized powders and their dielectric and magnetic properties

Double perovskite Ba2FeNbO6 (BFN) ceramics were prepared from the molten-salt synthesized BFN powders. The BFN powders have a cubic structure with $$ Fm\bar{3}m $$ space group, confirmed by X-ray diffraction patterns. Their average particle sizes increased with the annealing temperature and dwell time whereas decreased with the molten-salt content. X-ray photoemission spectra revealed both Fe2+ and Fe3+ ions present in the BFN powders and oxygen in the forms of lattice oxygen and oxygen vacancies, while niobium was present as Nb5+. The BFN ceramics exhibited significant frequency-dependent dielectric behavior, and two kinds of dielectric relaxor processes were observed. Their activation energies were 0.16 eV and 0.47 eV, respectively. The electron hopping process (between Fe2+ and Fe3+ ions) with the activation energy of 0.16 eV contributes the low-temperature dielectric relaxation process, and an activation energy of 0.47 eV associated with the high-temperature dielectric relaxation is originally from the barrier energy of the thermal motion of the oxygen vacancies. The dielectric relaxation observed at high-temperature region can be explained by Maxwell–Wagner interfacial polarization in the BFN ceramics. M–H plots of the BFN ceramics at different temperatures revealed their antiferromagnetic nature and a weak ferromagnetic behavior at 2 K. The remanent magnetization (Mr) of the BFN ceramics was measured to be 1.75 emu/g at 2 K and coercive field (Hc) as 1.26 kOe. Magnetization splitting was observed at ~ 290 K between the temperature-dependent magnetizations of the BFN ceramics, which were measured under zero field-cooled (ZFC) and field-cooled modes with an external field of 1 kOe. In the ZFC curve, a maximum peak was observed at 14 K, corresponding to the Neel temperature (TN). The TN of the present BFN ceramics shifts toward low temperature as compared with those prepared by conventional solid-state reaction methods. Such a reduction of the Neel temperature is ascribed to the size effect.

Microkinetic simulation and fitting of the temperature programmed reaction of methanol on CeO2(111): H2 and H2O + V production

The kinetics and mechanism for temperature programmed reaction following adsorption of an adsorbate can be better understood by simulation and fitting with comparison to experiment. A case study is presented here for the chemistry of adsorption of methanol on a CeO2(111) surface followed by heating. The gas products observed are CH3OH, CH2O, H2, H2O, CO, CO2. At low temperatures (< 500 K), there is formation of H2 and H2O, where the H2O formation is accompanied by lattice oxygen vacancy (V) formation and is thus important in determining the selectivity towards different products. Microkinetic modeling was performed using a recently published method for fitting to gain mechanistic knowledge of the H2 and H2O + V formation at < 500 K. In the kinetic models used here, most of the H2 and H2O + V formation can be explained by a mechanism in which a metastable state of hydrogen on the surface (H*) acts as an intermediate. Two possibilities were investigated for the source of the metastable H* intermediate: H* from CH bond breaking of methoxies, or promotion of H+ to H* via electron transfer from ionic methoxies absorbed in oxygen vacancies (CH3O−/V). From this study, we consider the latter to be more likely at < 500 K. For the H2O formation, it was found to be critical that H2O cannot dissociate directly on oxygen vacancies. Catalytic chemistry was observed in simulations, including catalytic formation of oxygen vacancies. Various features of the experimental results were reproduced, including methoxies being the major carbon containing species on the surface at < 500 K.

Effect of the Phase Composition and Local Crystal Structure on the Transport Properties of the ZrO2–Y2O3 and ZrO2–Gd2O3 Solid Solutions

The results of investigating the crystal structure, ionic conductivity, and local structure of the (ZrO2)1 –x(Gd2O3)x and (ZrO2)1 –x(Y2O3)x (x = 0.04, 0.08, 0.10, 0.12, and 0.14) solid solutions are reported. The crystals are grown by directional crystallization of the melt in a cold container. The phase composition of the crystals is investigated by X-ray diffractometry and transmission electron microscopy. The transport characteristics are studied by impedance spectroscopy in the temperature range of 400 to 900°C. The local crystal structure is examined by optical spectroscopy. Eu3+ ions were used as a spectroscopic probe. The study of the local structure of the ZrO2–Y2O3 and ZrO2–Gd2O3 solid solutions revealed the features in the formation of optical centers, which reflect the character of localization of oxygen vacancies in the crystal lattice depending on the stabilizing oxide concentration. It is established that the local crystal environment of Eu3+ ions in the (ZrO2)1 –x(Y2O3)x and (ZrO2)1 –x(Gd2O3)x solid solutions is determined by the stabilizing oxide concentration and is practically independent of the stabilizing oxide type (Y2O3 or Gd2O3). The maximum conductivity at a temperature of 900°C is observed in the crystals with 10 mol % of Gd2O3 and 8 mol % of Y2O3. These compositions correspond to the t'' phase and are close to the interface between the cubic and tetragonal phase regions. It is found that in the ZrO2–Y2O3 system the highly symmetric phase is stabilized at a lower stabilizing oxide concentration than in the ZrO2–Gd2O3 system. The analysis of the data obtained makes it possible to conclude that, in this composition range, the concentration dependence of the ionic conductivity is mainly affected by the phase composition rather than the character of the localization of oxygen vacancies in the crystal lattice.

Synthesis of C-doped TiO2 by sol-microwave method for photocatalytic conversion of glycerol to value-added chemicals under visible light

C-doped TiO2 photocatalyst synthesized using a one-step sol-microwave method with microcrystalline cellulose as the carbon source to achieve TiO2 of desirable visible light absorption, cluster size, surface area and band gap was applied in the photocatalytic oxidation of glycerol under visible light to produce value-added chemicals, for the first time. An increase in microwave irradiation time from 0 to 20 min reduced the anatase crystal size but increased the surface area, pore volume and pore radius. Carbon coupled with microwave treatment produced Ti3+ and oxygen vacancies in the TiO2 lattice of the C-doped TiO2 which yielded improved performance of the photocatalysts. For example, a cellulose loading at 10 % (i.e. 10 % Cel-TiO2(4-MW)) provided the highest photo-conversion of glycerol (67.5 %) and highest yields of glyceraldehyde (10.0 %), dihydroxyacetone (7.4 %), formic acid (49.0 %) and acetic acid (1.8 %). On the other hand, excess residual carbon on TiO2 surface (e.g. 20 % Cel-TiO2(0-MW)) retarded the activity of the photocatalyst.

Ti3+ Self-Doped Li4 Ti5 O12 Anchored on N-Doped Carbon Nanofiber Arrays for Ultrafast Lithium-Ion Storage.

Omnibearing acceleration of charge/ion transfer in Li4 Ti5 O12 (LTO) electrodes is of great significance to achieve advanced high-rate anodes in lithium-ion batteries. Here, a synergistic combination of hydrogenated LTO nanoparticles (H-LTO) and N-doped carbon fibers (NCFs) prepared by an electrodeposition-atomic layer deposition method is reported. Binder-free conductive NCFs skeletons are used as strong support for H-LTO, in which Ti3+ is self-doped along with oxygen vacancies in LTO lattice to realize enhanced intrinsic conductivity. Positive advantages including large surface area, boosted conductivity, and structural stability are obtained in the designed H-LTO@NCF electrode, which is demonstrated with preeminent high-rate capability (128 mAh g-1 at 50 C) and long cycling life up to 10 000 cycles. The full battery assembled by H-LTO@NCFs anode and LiFePO4 cathode also exhibits outstanding electrochemical performance revealing an encouraging application prospect. This work further demonstrates the effectiveness of self-doping of metal ions on reinforcing the high-rate charge/discharge capability of batteries.

Structural, magnetic, dielectric and optical properties of double-perovskite Bi2FeCrO6 ceramics synthesized under high pressure

We report on double-perovskite Bi2FeCrO6 ceramics synthesized by solid-state reaction under high pressure of 6 GPa and temperature of 1000 °C. Its crystal structure was refined by X-ray powder diffraction data, and the Bi2FeCrO6 ceramics crystallized in rhombohedral structure with R3c space group. The ceramic grains exhibited polyhedron morphology with average size of 2.80 μm. The atomic ratio of Bi:Fe:Cr was determined to be 2.04:1.00:1.00, close to the nominal value. X-ray photoelectron spectra confirmed the dual oxidation states of ion (Fe2+ and Fe3+) and chromium (Cr3+ and Cr6+) in the Bi2FeCrO6 ceramics and oxygen in the forms of lattice oxygen and oxygen vacancies. Bi2FeCrO6 ceramics exhibits both antiferromagnetic and ferromagnetic orders, which are reflected in the unique temperature dependent magnetization curves. In addition, Bi2FeCrO6 ceramics also have large dielectric constant (∼508 at 1 kHz) and small dielectric loss (0.38 at 1 MHz) at room temperature. The direct band gap of the Bi2FeCrO6 ceramics deduced from their UV–Vis–NIR absorption spectra, was ∼1.50 eV, which was small enough to absorb the sunlight at wavelengths below 829 nm. A strong absorption peak was also observed at 600 nm in the absorption spectra of the Bi2FeCrO6 ceramics. These findings demonstrate that the Bi2FeCrO6 ceramics with a narrow direct band gap can effectively absorb the main portion of the sunlight spectrum (i.e., visible lights) and have promising applications in the fields of photoelectrochemical devices and photovoltaic devices.

Influence of phase composition and local crystal structure on the transport properties of ZrO2−Y2O3 and ZrO2−Gd2O3 solid solutions

Abstract. The results of investigation of crystal structure, ion conductivity and local structure of solid solutions (ZrO2)1−x(Gd2O3)x and (ZrO2)1−x(Y2O3)x (x = 0.04, 0.08, 0.10, 0.12, 0.14). The crystals were grown by directional crystallization of the melt in a cold container. The phase composition of the crystals was studied by X−ray diffractometry and transmission electron microscopy. Transport characteristics were studied by impedance spectroscopy in the temperature range 400—900 °C. The local crystal structure was studied by optical spectroscopy. Eu3+ ions were used as a spectroscopic probe. The results of the study of the local structure of solid solutions of ZrO2—Y2O3 and ZrO2—Gd2O3 systems revealed the peculiarities of the formation of optical centers, which reflect the nature of the localization of oxygen vacancies in the crystal lattice depending on the stabilizing oxide concentration. It is established that the local crystal environment of Eu3+ Ions in solid solutions (ZrO2)1−x(Y2O3)x and (ZrO2)1−x(Gd2O3)x is determined by the stabilizing oxide concentration and practically does not depend on the type of stabilizing oxide (Y2O3 or Gd2O3). The maximum conductivity at 900 °C was observed in crystals containing 10 mol.% Gd2O3 and 8 mol.% Y2O3. These compositions correspond to the t′′−phase and are close to the boundary between the regions of the cubic and tetragonal phases. It was found that in the system ZrO2—Y2O3 stabilization of the highly symmetric phase occurs at a lower stabilizing oxide concentration than in the system ZrO2—Gd2O3. Analysis of the data obtained allows us to conclude that in this range of compositions the main influence on the concentration dependence of the ion conductivity has a phase composition, rather than the nature of the localization of oxygen vacancies in the crystal lattice.

Promotive effect of H2O on low-temperature NO reduction by CO over Pd/La0.9Ba0.1AlO3-

Abstract For future removal of NOx by catalysts, low-temperature NO reduction is desired. Results confirmed that a drastic improvement of catalytic activity by H2O on NO–CO–O2 reaction over Pd/La0.9Ba0.1AlO3-δ catalyst at the low temperature of 473 K or below. In a humidified condition, NO reaction with CO on Pd/La0.9Ba0.1AlO3-δ proceeded without being affected by competitive adsorption of NO and CO, whereas that on Pd/Al2O3 was inhibited by strong adsorption of CO on a Pd surface. From in-situ DRIFTS measurements, results showed that nitrite species on the support react with CO adsorbed onto Pd at the periphery of Pd particles and that carbonate species accumulated on Pd/La0.9Ba0.1AlO3-δ are removed rapidly in a humidified condition. Although NO reduction proceeds dominantly on the Pd surface in a dry condition, supplied steam promotes desorption of the surface carbonate to advance the reaction of nitrite with CO for de-NOx in a humidified condition. This mechanism occurs specifically on Pd/La0.9Ba0.1AlO3-δ by virtue of the lattice oxygen and oxygen vacancy on La0.9Ba0.1AlO3-δ.

Catalytic Oxidation of VOCs over SmMnO3 Perovskites: Catalyst Synthesis, Change Mechanism of Active Species, and Degradation Path of Toluene.

Highly active samarium manganese perovskite oxides were successfully prepared by employing self-molten-polymerization, coprecipitation, sol-gel, and impregnation methods. The physicochemical properties of perovskite oxides were investigated by XRD, N2 adsorption-desorption, XPS, and H2-TPR. Their catalytic performances were compared via the catalytic oxidation of toluene. The perovskite prepared by self-molten-polymerization possessed the highest catalytic capacity, which can be ascribed to its higher oxygen adspecies concentration (Olatt/Oads = 0.53), higher surface Mn4+/Mn3+ ratio (Mn4+/Mn3+ = 0.95), and best low-temperature reducibility (H2 consumption = 0.27; below 350 °C). The most active catalyst also exhibited good cycling and long-term stability for toluene oxidation. After a multistep cycle reaction and a long-term reaction of 42 h, the toluene conversion maintained above 99.9% at 270 °C. Mechanistic study hinted that lattice oxygen was involved in toluene oxidation. The oxidation reaction was dependent on the synergism of lattice oxygen, adsorbed oxygen, and oxygen vacancies. The degradation pathway of toluene, researched by diffuse reflectance infrared Fourier transform spectroscopy and online mass spectrometry technologies, demonstrated that a series of organic byproducts existed at a relatively low temperature. This work provides an efficient and practical method for selecting highly active catalysts and for exploring the catalytic mechanism for the removal of atmospheric environmental pollution.

Microscopic mapping of dopant content and its link to the structural and thermal stability of yttria-stabilized zirconia polycrystals

The effect of yttria content on structural and thermal stability of zirconia in yttria-stabilized zirconia (YSZ) polycrystalline ceramics was systematically investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. Taking advantage of an experimentally retrieved linear dependence of Raman bandwidth on yttria content, Raman imaging was applied as an effective tool in examining the local yttrium distribution in YSZ ceramics and its relationship with environmentally driven polymorphic transformation. A significant variation of monoclinic fraction with yttria content and temperature was found and interpreted according to a newly proposed model, which takes into account the change in lattice hydroxyl and oxygen vacancies and the possible formation of stable defect complexes.

Proton Conducting Lithium Super Ionic Conductor for Intermediate Temperature Solid Oxide Electrolyzer Cell

Proton conducting solid oxide electrolyzer cell (SOEC) enables economic production of hydrogen gas at intermediate temperatures (400- 700 °C). Lithium super ionic conductors are solid state electrolytes with very high lithium ion conductivity in the order of 10-2 to 10-4 S/cm at room temperature1. At temperature range 60 – 300 °C, the lithium ion conductivity reaches around 1 to 10-2 S cm-1. Mechanism of the lithium ion transport starts with ions at local sites being excited to neighboring sites and collectively diffusing on a macroscopic scale. Under electrical field, long distance transport is realized by continuous hopping of Li+ ions2. However, in moisture containing ambient atmosphere, proton−lithium ion (H+/Li+) exchange takes place on the surface of the electrolyte making it unsuitable for Li-ion batteries. It has been shown that the exchange occurs readily when Li stoichiometry is greater than 3 atoms per formula3, 4. One such reaction is given below5: Li6.4La3Zr1.4Ta0.6O12 + xH2O → Li6.4-xHxLa3Zr1.4Ta0.6O12 + xLiOH After fully replacing the mobile lithium ions by protons, the solid electrolyte acts as a proton conductor. Very few works reported such lithium compounds for proton conduction and proton conductivity is several orders higher when compared to other standard electrolytes6. In this work, we demonstrate for the first time the proton conduction behavior of garnet type ceramic Li6.4La3Zr1.4Ta0.6O12 electrolyte with a completely new mechanism of conduction of protons demonstrating the highest protonic conductivity of 8.1 x 10-2 S cm-1 and chemically stable upto 200hrs in 50% moisture/Argon atmosphere at 600 °C. Ceramic type lithium super ionic conductors which are stable at very high temperatures (up to 1100 °C) and are suitable for intermediate temperature (400- 600 °C) solid oxide electrolyzer cells (SOEC). The mechanism of proton conduction in lithium super ionic conductor is entirely different from the standard electrolytes. While proton conduction in the latter is through oxygen vacancies in the crystal lattice, the proton conduction in the former is by diffusion and migration of protons through lithium ions sites in the crystal lattice6. The proton – lithium exchange is also reversible when the electrolyte is flushed with 1M LiOH3. The high proton conductivity suggests that garnet-based ceramics represents a new class of proton conductors that could be effectively used in SOEC’s for hydrogen generation at intermediate operating temperatures.

Influence of A-site deficiency on structural evolution of Pr2-xNiO4+δ with temperature

We report on the structural evolution with temperature of layered A-site deficient Pr2-xNiO4+δ (x = 0–0.2) with the K2NiF4 structure. Data of neutron diffraction and thermogravimetric analysis reveals that Pr deficiency causes generation of lattice oxygen vacancies on equatorial and apical sites but does not influence the concentration of interstitial oxygen. High-temperature X-ray diffraction shows for all materials a reversible orthorhombic-to-tetragonal phase transition with negligible hysteresis in the range ~400–450 °C, reducing tilting and twisting of the NiO6 octahedra. The phase transition temperature is found to decrease slightly with increasing A-site deficiency. Thermal decomposition to Pr4-zNi3O10-y and Pr6O11 is found to occur in the temperature range 580–800 °C with apparent activation energy 166–221 kJ/mol.

Large-Pore Mesoporous CeO2 -ZrO2 Solid Solutions with In-Pore Confined Pt Nanoparticles for Enhanced CO Oxidation.

Active and stable catalysts are highly desired for converting harmful substances (e.g., CO, NOx ) in exhaust gases of vehicles into safe gases at low exhaust temperatures. Here, a solvent evaporation-induced co-assembly process is employed to design ordered mesoporous Cex Zr1- x O2 (0 ≤ x ≤ 1) solid solutions by using high-molecular-weight poly(ethylene oxide)-block-polystyrene as the template. The obtained mesoporous Cex Zr1- x O2 possesses high surface area (60-100 m2 g-1 ) and large pore size (12-15 nm), enabling its great capacity in stably immobilizing Pt nanoparticles (4.0 nm) without blocking pore channels. The obtained mesoporous Pt/Ce0.8 Zr0.2 O2 catalyst exhibits superior CO oxidation activity with a very low T100 value of 130 °C (temperature of 100% CO conversion) and excellent stability due to the rich lattice oxygen vacancies in the Ce0.8 Zr0.2 O2 framework. The simulated catalytic evaluations of CO oxidation combined with various characterizations reveal that the intrinsic high surface oxygen mobility and well-interconnected pore structure of the mesoporous Pt/Ce0.8 Zr0.2 O2 catalyst are responsible for the remarkable catalytic efficiency. Additionally, compared with mesoporous Pt/Cex Zr1- x O2 -s with small pore size (3.8 nm), ordered mesoporous Pt/Cex Zr1- x O2 not only facilitates the mass diffusion of reactants and products, but also provides abundant anchoring sites for Pt nanoparticles and numerous exposed catalytically active interfaces for efficient heterogeneous catalysis.

Synergistic effects of binary oxygen carriers during chemical looping hydrogen production

The use of binary oxygen carrier allows for the materials of enhanced activity or stability during chemical looping process. However, the lack of mechanical understanding of the origin of the improvements hindered the rational design and control of the doping process in the oxygen carrier production. Here, we synthesized a series of M0.6Fe2.4Oy (M = Ni, Cu, Co, Mn) binary spinel materials and carried out various characterization techniques to study how the dopants influenced the material phase change, the oxygen transfer as well as the chemical looping performance. The results showed the chemical looping reactivity can be related to the oxygen transformation between lattice oxygen and oxygen vacancy, which was determined by the redox properties of both dopants and iron. The metal in tetrahedral site for Cu, Mn, Ni-doped sample were relatively stable, limiting oxygen transformation ability. In comparison, Co dopant promoted the reducibility of iron in tetrahedral site as well as metals in other sites, making almost all lattice oxygen rapidly transformed to oxygen vacancy during reduction. This was the main cause for the subsequent high hydrogen production rate (average ∼0.02 mmol. g−1.s−1) and yield (∼15.9 mmol.g−1). Upon cycling, the phase separation of single oxides from Co0.6Fe2.4Oy and Mn0.6Fe2.4Oy spinels led to the decreased ability of oxygen transformation. However, the performance was extremely stable for Cu0.6Fe2.4Oy with reversible phase change between spinel and (Fe, Cu) wusitite by the Cu-Fe interaction. Based on the current results, this work points to a promising Cu-Co co-doping material with both good reactivity and stability.

Engineering Interface and Oxygen Vacancies of NixCo1-xSe2 to Boost Oxygen Catalysis for Flexible Zn-Air Batteries.

Exploring efficient bifunctional oxygen electrocatalysts is a critical element for developing high-power-density metal-air batteries. Here, we propose an interface and oxygen vacancy engineering strategy to integrate subtle lattice distortions, oxygen vacancies, and nanopores on the surface of NixCo1-xSe2-O interface nanocrystals, which exhibit efficient bifunctional catalytic performances for oxygen evolution and reduction. The results from X-ray absorption spectroscopy and electron spin resonance spectroscopy demonstrate that the defect structure can enlarge the number of active sites for electrocatalytic performances. Flexible Zn-air battery using NixCo1-xSe2-O as a cathode displays large specific capacity and remarkable stability even after twisting at any angle, thus showing potential for wearable and portable electronic device application. The implementation of our method provides a powerful strategy for preparing advanced catalysts for energy utilization.

Comparison of Structural and Transport Properties of Zirconia Single-Crystals Stabilized by Yttria and Gadolinia

The results of the study of the crystal structure, ionic conductivity and local structure of (ZrO2)1- х(Gd2O3)x and (ZrO2)1- х(Y2O3)x solid solutions in a wide range of compositions (x = 0.04-0.38) are given. Studies were performed on crystals obtained by the method of directional crystallization of the melt in a cold crucible. The results of the study of the local structure of the solid solutions of the ZrO2-Y2O3 and ZrO2-Gd2O3 systems revealed the formation of optical centers, which reflect the localization of oxygen vacancies in the crystal lattice depending on the concentration of the stabilizing oxide. It was shown that the local crystalline environment of Eu3+ ions in solid solutions (ZrO2)1- х(Y2O3)x and (ZrO2)1- х(Gd2O3)x is determined by the concentration of the stabilizing oxide and practically does not depend in this case on the type of the stabilizing oxide. The maximum conductivity of ZrO2-Gd2O3 solid solutions is shifted to higher concentrations relative to the maximum conductivity of ZrO2-Y2O3 solid solutions and was observed on crystals corresponding to the t´´ phase. The results of the study of the crystal and local structure of solid solutions of the ZrO2-Gd2O3 and ZrO2-Y2O3 systems allowed us to isolate the concentration regions of stabilizing oxides in which the ionic conductivity is determined mainly by the phase composition or localization of oxygen vacancies in the crystal lattice.

Simple solvent-free synthesis of rod-like Cu-doped V2O5 for high storage capacity cathode materials of lithium ion batteries

Rod-like Cu-doped V2O5 were synthesized by an extraordinary simple solid-state chemical route. Cu doping not only increases the cell volume, but also introduces abundant oxygen vacancies in V2O5 crystal lattice, which is benefit for fast electron and ion transport during charging-discharging process. As a result, the rod-like Cu-doped V2O5 exhibited a high discharge specific capacity of 293.1 mA h g−1 at 1 C, much higher than the undoped V2O5 with the capacity of 235.5 mA h g−1 and almost reaching to the theoretical capacity of 294 mA h g−1. This simple and environment-friendly route to prepare advanced cathode shows great potential for industrial application in energy storage field.

Improved nonlinear absorption mechanism of tin oxide thin films: Role of strontium doping

We report the effect of strontium doping on third-order nonlinear optical properties of tin oxide (SnO2) thin films grown via chemical spray pyrolysis technique. The X-ray diffraction (XRD) results reveal that films exhibit a polycrystalline phase with a tetragonal crystal structure. The broadening and shifting of diffraction peak indicate that the dopant Sr2+ ion successfully replaced the Sn sites of SnO2 lattice. The reduction of crystalline size from 23.92 to 12.96 nm indicates the assimilation of point defects such as interstitial and oxygen vacancies in the SnO2 lattice upon doping. The surface morphological analysis via atomic force microscopy indicates the shattering of grains into small particles upon Sr doping. The energy band gap of films shows a substantial drop from 3.97eV to 3.03eV due to the formation of sub-band levels in the forbidden gap. Photoluminescence (PL) spectra show intense, broad asymmetric emission bands centred around 390 nm and extending up to 500 nm. The third order nonlinear absorption mechanism observed in Sr: SnO2 films were attributed to free carrier absorption (FCA) induced two-photon absorption (TPA). The third order nonlinear absorption co-efficient βeff shows a one order enhancement (0.14 × 10−1 cm/W to 3. 91 × 10−1 cm/W) which indicates that competency of grown films in nonlinear optical device applications.