Effect of cobalt doping on the dielectric response of B0.95Pb0.05TiO3B_{0.95}Pb_{0.05}TiO_3 ceramics

Dielectric response of Ba 0.95 Pb 0.05 TiO 3 ceramics doped with 0.1 and 1 wt.% of Co 2 O 3 , synthesized by conven- tional high-temperature method, wa s studied in wide temperature and frequency range. The temperature dependences of the real and the imaginary parts of dielectric permittivity of the ceramics were compared with those of BaTiO 3 and Ba 0.95 Pb 0.05 TiO 3. The addition of Co 3+ ions results in a broadening of dielectric anom- alies related to the transition to p araelectric cubic phase, and the structural transition between the tetragonal and the orthorhombic phases. At low temperatures (125 – 200 K) the dielectric absorp- tion of Co-doped Ba 0.95 Pb 0.05 TiO 3 ceramics was found to exhibit relaxor-like properties. The die lectric response has been found to contain the contributions characte ristic of fluctuations of the polar nanoregion boundaries and reorientations of the dipole moments between allowed directions in the nanoregions in the rhombohe- dral and the orthorhombic phases. The behavior speaks in favor of ordering of polar defects in the host lattice of Ba 0.95 Pb 0.05 TiO 3 in a form polar nanoregions

Investigations of LiNb1−xTaxO3 nanopowders obtained with mechanochemical method

Nanocrystalline compounds LiNb1−xTaxO3 of various compositions (x = 0, 0.25, 0.5, 0.75, 1) were synthesized by high-energy ball milling of the initial materials (Li2CO3, Nb2O5, Ta2O5) and subsequent high-temperature annealing of the resulting powders. Data on the phase composition of the nanopowders were obtained by X-ray diffraction methods, and the dependence of the structural parameters of LiNb1−xTaxO3 compounds on the value of x was established. As a result of the experiments, the optimal parameters of the milling and annealing runs were determined, which made it possible to obtain single-phase compounds. The Raman scattering spectra of LiNb1−xTaxO3 compounds (x = 0, 0.25, 0.5, 0.75, 1) have been investigated. Preliminary experiments have been carried out to study the temperature dependences of their electrical conductivit

Nanoporous titanium borophosphates with rigid gainesite-type framework structure

China Scholarship Council (CSC); National Natural Science Foundation of China [40972035]Nanoporous titanium borophosphates have been synthesized which exhibit a rigid gainesite-type framework of polyhedra. The open-framework character is supported by the reversibility of de-and rehydration processes

Anomalous Thermal Expansion of HoCo0.5Cr0.5O3 Probed by X-ray Synchrotron Powder Diffraction

Abstract Mixed holmium cobaltite-chromite HoCo0.5Cr0.5O3 with orthorhombic perovskite structure (structure type GdFeO3, space group Pbnm) was obtained by solid state reaction of corresponding oxides in air at 1373 K. Room- and high-temperature structural parameters were derived from high-resolution X-ray synchrotron powder diffraction data collected in situ in the temperature range of 300–1140 K. Analysis of the results obtained revealed anomalous thermal expansion of HoCo0.5Cr0.5O3, which is reflected in a sigmoidal temperature dependence of the unit cell parameters and in abnormal increase of the thermal expansion coefficients with a broad maxima near 900 K. Pronounced anomalies are also observed for interatomic distances and angles within Co/CrO6 octahedra, tilt angles of octahedra and atomic displacement parameters. The observed anomalies are associated with the changes of spin state of Co3+ ions and insulator-metal transition occurring in HoCo0.5Cr0.5O3

Synthesis and characterization of perovskite-type La1−yCayMn1−xBx″O3±δLa_{1-y}Ca_{y}Mn_{1-x}B^{″}_{x}O_{3±δ} nanomaterials (B″ = Ni, Fe; x = 0.2, 0.5; y = 0.4, 0.25)

Perovskite-type nanomaterials of the compositions $La_{1-y}Ca_{y}Mn_{1-x}B^{″}_{x}O_{3±δ}$ with B’’ = Ni, Fe; x = 0.2, 0.5 and y = 0.4, 0.25 were prepared using two different preparation routes (synthesis by precipitation and the PVA/sucrose method) at 500 °C–700 °C. The calcined products of the syntheses were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and physisorption measurements. The materials from the PVA/sucrose method contain particles with diameters from 33 nm to 48 nm, generate specific surface areas up to 33 m2/g and form pure compared to 45 nm–93 nm and up to 18 m$^2$/g from precipitation method which contain a significant amount of sodium ions. The agglomeration process was analyzed for one nanomaterial (B’’ = Fe, x = 0.2, y = 0.4) from the PVA/sucrose method using temperature dependent XRD showing only a slight growth (4.3%) of nanoparticles at 600 °C. The materials from the PVA/sucrose method turned out to be more suitable as electrode materials in electrochemical applications (SOFC, sensors) because of smaller particle sizes, higher specific surface areas and purity

Anomalous High Temperature Structural Behavior of Potential Multifunctional Material SmCo0.5_{0.5}Cr0.5_{0.5}O3_3

Crystal structure parameters of the mixed cobaltite–chromite SmCo$_{0.5}$Cr$_{0.5}$O$_3$ in the temperature range of 298–1173 K were derived from in situ high‐resolution X‐ray synchrotron powder diffraction data. Similar to the parent SmCoO$_3$ compound, SmCo$_{0.5}$Cr$_{0.5}$O$_3$ reveals anomalous thermal expansion reflected in abnormal temperature dependence of the unit cell dimensions and the selected interatomic distances and angles. These anomalies are associated with temperature induced changes of spin state of Co$^{3+}$ ions and coupled insulator‐metal transition. Observed decreasing behavior of the bandwidth W points on the increasing population of the exited spin states of Co$^{3+}$ ions in SmCo$_{0.5}$Cr$_{0.5}$O$_3$ with increasing temperature. First principle calculations revealed antiferromagnetic ground state of SmCo$_{0.5}$Cr$_{0.5}$O$_3$ as the most stable

Synthesis and Electrochemical Performances of gamma-KCoPO4 Nanocrystals as Promising Electrode for Aqueous Supercapatteries

Herein, discrete gamma-KCoPO4 nanocrystals were prepared by a facile, green and fast sol-gel route. The lattice parameters as well as positional and displacement parameters of atoms in the average gamma-KCoPO4 structure with a space group of P2(1)/n were calculated using full profile Rietveld refinement. Monodispersed quadrangular gamma-KCoPO4 nanocrystals with improved phase purity and crystallinity were found through XRD patterns and HRTEM images. Subsequently, the prepared gamma-KCoPO4 nanocrystals were tested as electrode material for supercapatteries in aqueous electrolytes. The gamma-KCoPO4 electrode shows superior specific charge capacity of 309 C g(-1) at 1 mV s(-1) in 1 M KOH, compared to 1 M NaOH (222 C g(-1)) and 1 M LiOH (77 C g(-1)). Further, it exhibits improved electrochemical activity by delivering an impressive specific charge capacity of 100 C g(-1) at a current of 0.6 mA cm(-2) in an aqueous electrolyte medium with acceptable capacity retention. A lab-scale supercapattery was assembled resembling the commercial device. The fabricated device delivered an enhanced specific energy of 28 W h kg(-1) and a specific power of 1600 W kg(-1) and prolonged cycle life of about 5000 cycles

New Mixed Y0.5R0.5VO4 and RVO4:Bi Materials: Synthesis, Crystal Structure and Some Luminescence Properties

The results are reported on a precise crystal structure and microstructure determination of new mixed YVO4-based orthovanadates of Y0.5R0.5VO4 (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) as well as some Bi3+-doped RVO4 (R = La, Gd, Y, Lu) nano- (submicro-) materials. The formation of continuous solid solutions in the YVO4–RVO4 pseudo-binary systems (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) has been proved. The lattice constants and unit cell volumes of the new mixed orthovanadates were analyzed as a function of R3+ cation radius. The impact of crystal structure parameters on the energy band gap of the materials was studied by means of photoluminescence studies of the Bi3+-doped compounds