Cesium Vanadate Research Articles

Luminescence mechanism and energy transfer in cesium metavanadate CsVO3

Photoluminescence properties and relaxation dynamics of electronic excitations in cesium vanadate CsVO3 have been studied upon pulse laser excitation in the wide temperature range of 6.5–300 K. A vibronic structure observed in low-temperature PL spectra is considered and interpreted. Peculiarities of luminescence relaxation dynamics and emission spectra of CsVO3 along with the appearance of the vibronic structure are explained in terms of strong electron-phonon coupling of excited electronic states and centrosymmetric vibrational modes in [VO4]3- center. A new approach in an interpretation of luminescence processes in vanadates is demonstrated.

Stability of Molten-Phase Cs–V–O Catalysts for SO3 Decomposition in Solar Thermochemical Water Splitting

Supported molten cesium vanadate catalysts (Cs–V–O/SiO2) showed activities comparable to that of a reference Pt catalyst (1 wt % Pt/TiO2) for SO3 decomposition at moderate temperatures (∼600 °C), which is essential as an O2 evolution reaction in solar thermochemical water splitting cycles. Stability testing of the catalyst over a 1000 h continuous reaction at 600 °C resulted in deactivation by ∼20% of the initial activity. Kinetic analysis of the activity versus time-on-stream indicated that the observed deactivation behavior can be divided into an induction period (≤100 h) and an acceleration period (>100 h). The deactivation is mainly caused by the vaporization loss of active components (Cs and V) from the molten phase. At the earliest stage, most vapor is generated in the upstream section of the catalyst bed and then redeposits therebelow. Upon repeating these vaporization and deposition cycles, Cs and V move gradually downstream. During this induction period, the deactivation is not obvious because th...

A visible-light-driven photocatalyst of cesium vanadate Cs2V4O11 nanowires by hydrothermal method

A new visible-light-driven photocatalysts of Cs2V4O11 nanowires with extremely high length–diameter ratio were synthesized by the conventional hydrothermal reaction. The sample was characterized by XRD measurement and structure refinement, scanning electron microscope (SEM) and UV–vis absorption spectra. Cs2V4O11 nanowire has efficient absorption in the UV–visible light wavelength region with a band gap energy of 2.47eV and an indirect allowed electronic transition. Photocatalytic activities of Cs2V4O11 nanowires by photo-degradation reaction of methylene blue (MB) were investigated under visible-light irradiation in air. Cesium vanadate nanowires show a high photocatalytic activity and could be a potential photocatalyst driven by visible-light.

Crystal Growth, Structure, Polarization, and Magnetic Properties of Cesium Vanadate, Cs2V3O8: A Structure–Property Study

Cesium vanadate, Cs2V3O8, a member of the fresnoite-type structure, was synthesized via a hydrothermal route and structurally characterized by single-crystal X-ray diffraction. Cs2V3O8 crystallizes in a noncentrosymmetric polar space group, P4bm, with crystal data of a = 8.9448(4) Å, c = 6.0032(3) Å, V = 480.31(4) Å(3), and Z = 2. The material exhibits a two-dimensional layered crystal structure consisting of corner-shared V(5+)O4 and V(4+)O5 polyhedra. The layers are separated by the cesium cations. The alignment of the individual polyhedra results in a macroscopic polarity for Cs2V3O8. Frequency-dependent polarization measurements indicate that the material is not ferroelectric. A pyroelectric coefficient of -2.0 μC m(-2) K(-1) was obtained from pyroelectric measurements taken as a function of the temperature. The magnetic susceptibility data were measured as a function of the temperature and yielded an effective magnetic moment of 1.78 μB for the V(4+) cation. Short-range magnetic ordering was observed around 7 K. The susceptibility data were fit to the Heisenberg square-lattice model supporting that the short-range magnetic interactions are antiferromagnetic and two-dimensional. IR and thermal properties were also characterized.

Simulation of oxidation of carbon particles at the surface of mixed oxide catalysts

A model of catalytic oxidation of a cylindrical carbon particle was suggested. The model considers the rate of layer-by-layer burning of the particle, variation of its geometry, and remote action of the catalyst. A software for calculations was developed; the data obtained correlate well with the experimental data for catalysts based on lanthanum cesium vanadate. The kinetics of carbon oxidation on catalysts of varied nature was compared.

Physical properties of alkali and mixed lithium–cesium vanadate glasses prepared over an extended range of compositions

We report glass transition temperatures and density measurements of alkali and mixed alkali vanadate glasses. The glass formation of the alkali vanadate glasses ( RM 2O·V 2O 5), which required rapid cooling, occurred in the range R=0.00–1.50, where M is the alkali. We also studied the mixed alkali vanadate glasses [(( RX)Li 2O+ R(1− X)Cs 2O)·V 2O 5] with R=0.60 and X in the range 0.00–1.00, where we discovered a narrow region of bulk glass formation centered on X=0.60. We also compared molar volumes of the alkali vanadates to the analogous alkali phosphates [1,2]. Predicted molar volumes, determined from densities of the respective oxides, were found to closely agree with experimental values for the glasses. Unlike the alkali borates, silicates, and germanates, lithium phosphates and vanadates exhibited molar volumes indicative of structural expansion.

The Crystal Structure of Cs2TiSi6O15

Crystals of a new titanosilicate phase, Cs2TiSi6O15, were grown from a cesium vanadate flux. The compound has monoclinic symmetry, space groupC2/c, witha=13.386(5),b=7.423(3),c=15.134(5) Å,β=107.71(3)°,Z=4. The crystal structure was solved using single crystal X-ray data (MoKαradiation) and refined toR(F)=0.039 for 1874 unique reflections. In the structure, isolated titanium-centred octahedra and silica-centred tetrahedra share all corners to form an open framework structure containing large cavities in which the cesium ions are located. Each cavity is bound by three 5-rings, two 6-rings, and two 8-rings. The cavities are linked via the 8-rings into channels parallel to [101]. The cesium ions occur in pairs along the channels, separated by 3.765(2) Å.

Thermoelectric power of ferroelectric potassium vanadate, cesium vanadate, lithium vanadate and their solid solutions

The thermoelectric power of the vanadates of potassium, cesium and lithium and their solid solutions was measured in the temperature range covering their transition points. The thermoelectric power measurement was carried out by the two-electrode technique for pellets of polycrystalline ceramic samples. The thermoelectric power increased with temperature initially, then decreased attaining a zero value at the transition temperature. As the concentration of KVO3 increased the thermoelectric power decreased for the solid solutions (K x − Cs1−x )VO3, whereas the thermoelectric power increased with increase in concentration of KVO3 for the solid solutions (K x − Li1−x )VO3. Vanadates of potassium, cesium, and lithium and their solid solutions showedP type semiconductor behaviour in ferroelectric state andn type semiconductor behaviour in paraelectric region.

Thermoelectric power of undoped and aluminium oxide doped ferroelectric potassium vanadate and cesium vanadate

Abstract The thermoelectric power(s) of pure and aluminium oxide doped ferroelectric potassium vanadate and cesium vanadate have been determined in the temperature range covering their transition temperature. The thermoelectric power is found to increase linearly with temperature, attains maximum value and with further increase in temperature decreases to zero indicating transition temperature of the respective samples while it changes sign for higher temperature. The thermoelectric power of KVO3 and CsVO3 increases with increase in doping concentration of Al2O3up to 0.1 mol. %, however, it decreases with further increase in doping concentration. It is observed that pure and aluminium doped KVO3 and CsVO3 materials show p-type behaviour in ferroelectric state andn-type behaviour in paraelectric state.

Studies on dielectric and hysteresis properties of undoped and aluminium oxide doped ferroelectric cesium vanadate

The effect of aluminium doping, as an acceptor impurity on the polycrystalline cesium vanadate has been studied in the temperature range covering their transition points. The dielectric constant is measured by 'comparison of capacities' while the coercive field is evaluated using hysteresis loop. It is seen that the dielectric constant as well as the coercive field are remarkably depending on doping concentrations. They increase significantly up to 0.1 mol% Al2O3, however, decrease for higher concentrations. The Curie temperature of all the samples of cesium vanadate decreases with increasing aluminium concentrations.

Investigation of pyroelectric characteristics of Al 2O 3 doped KVO 3 and CsVO 3

The pyroelectric properties of undoped and aluminium-oxide doped potassium vanadate and cesium vanadate have been studied in the temperature range covering their transition points. The values of pyroelectric current and coefficient of undoped and Al 2O 3-doped KVO 3 and CsVO 3 show a sharp peak at their Curie temperature. These Curie temperatures are consistent with those investigated by dielectric-constant measurements and the hysteresis-loop method. The Curie temperatures of KVO 3 and CsVO 3 doped with Al 2O 3 decrease with, increasing dopant concentrations.

High‐pressure Raman study of CsVO3 and pressure‐induced phase transitions

AbstractThe pressure dependence of the Raman frequencies of cesium vanadate (CsVO3) was studied using a diamond anvil cell up to 15 GPa. From the abrupt changes in the Raman specta three pressure‐induced phase transitions are inferred at 10, 11.5 and 13 GPa. The first phase transition, at 10 GPa, is subtle but affects the VO bond length. It is believed that this transition is of the same nature as that observed in postassium and rubidium vanadates. The much higher transformation pressure in CsVO3 is attributed to the anomalous compressibility of the Cs+ ion. The second phase transition involves more drastic changes in the high‐frequency region. This is attributed to the rotations and distortions in the VO4 tetrahedra which lower the symmetry of the lattice. In the third phase transition, the appearance of broader Raman peaks and the disappearance of the chain deformation modes suggest a partial disorder in the chain structure.

Studies on dielectric hysteresis of ferroelectric sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions

The dielectric hysteresis property of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions has been studied in the temperature range covering their transition points. The hysteresis loop method is used for coercive field measurements. It was observed that the coercive field decreases with increasing temperature, and that it also decreases with increasing sodium concentration in the solid solutions (sodium-rubidium) vanadate and (sodium-cesium) vanadate.

Electrical conductivity of ferroelectric sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions

The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO3, RbVO3 and CsVO3, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric state and depends upon sodium concentration.

Single crystal syntheses by the electrolyses of molten titanates, molybdates and vanadates

Electrolyses of alkali titanate and titanate-vanadate melts at temperatures up to 1050°C have produced single crystals of a number of phases of general composition A x BO 2 where A is an alkali-metal ion and B represents a mixture of Ti 3+ and Ti 4+ or of V 3+ and Ti 4+. These phases included hexagonal Na 1.3V 1.3Ti 0.7O 4, with lattice parameters a = 2.92, c = 11.20 Å, the hollandite-types K x Ti 4O 8 ( a = 10.20, c = 2.99 Å) and Cs x Ti 4O 8 ( a = 10.32, c = 2.92 Å), a potassium layer compound K 0.8V 0.8Ti 1.2O 4 ( a = 3.73, b = 15.90, c = 2.98 Å) and a cesium layer compound Cs x Ti 2O 4 isomorphous with Rb x Mn x Ti 2− x O 4, with a = 3.84, b = 18.02, c = 3.01 Å. We have also found a monoclinic sodium titanium oxide of composition near to NaTiO 2, with a = 23.4, b = 3.08, c = 11.06 Å, β = 75.25°, and an octatitanate K 3Ti 8O 17, with a = 15.68, b = 3.809, c = 12.06 Å and β = 95.0°. Electrolyses of cesium vanadate and molybdate melts have also produced new phases, including a tetragonal cesium vanadium bronze Cs 0.93V 2O 5+ x , x ≈ 0.3, with a = 7.72, c = 11.73 Å, and a monoclinic cesium molybdenum bronze Cs 0.3MoO 3. The structures of a number of the phases produced have been determined or identified. Most are poor conductors of electricity, but Cs x Ti 4O 8 shows highly anisotropic semiconductivity.