Upadhyayula V Varadaraju

Thermal expansion behaviour of sodium zirconium phosphate structure type phosphates of the formula AM3+SnP3O12 (A = Ca, Sr and Ba; M3+ = Cr and Fe) was studied by high temperature X-ray diffraction and dilatometry in the temperature range 298-1073K. The variation in the hexagonal lattice parameters of the Ca-containing compounds is in line with the 'sodium zirconium phosphate behaviour'. However, the strontium- and barium-containing compounds display an altogether different behaviour of axial expansion. The results are explained based on the crystal chemistry of these compounds. © 2003 Elsevier Ltd. All rights reserved.

LiCo1-xMxPO4 (M = Mg2+, Mn 2+ and Ni2+; 0 ≤ x ≤ 0.2) compounds have been synthesized by solid-state reaction method and studied as cathode materials for secondary lithium batteries. LiCoPO4 exhibits a discharge plateau at ∼4.7 V with an initial discharge capacity of 125 mAh/g and on cycling capacity falls. Substitution of Co2+ with Mg2+/Mn 2+/Ni2+ in LiCoPO4 has an influence on the initial discharge capacity and on cycling behaviour. The capacity retention of LiCoPO4 is improved by manganese substitution. Among the manganese substituted phases, LiCo0.95Mn0.05PO4 shows good reversible capacity of ∼50 mAh/g. © 2005 Elsevier Ltd. All rights reserved.

LiCoAsO4 is synthesized by solid state reaction method and its crystal structure has been refined by the Rietveld method using powder X-ray diffraction data. LiCoAsO4 crystallizes in olivine structure with space group Pnma and orthorhombic lattice parameters are a = 10.4614(2) Å, b = 5.9970(1) Å and c = 4.8866(1) Å. Electrochemical studies reveal that in LiCoAsO4, lithium is deintercalated and intercalated at high voltage ∼5.0 V. On the other hand, the compound can react with about 9Li on discharge to 0.05 V. A reversible capacity of ∼100 mAh/g is obtained in the voltage range 1.0-2.5 V. © 2005 Elsevier Ltd. All rights reserved.

Eu3+ luminescence was used as a structural probe in understanding the preferential site occupancy of lone pair cation, Bi 3+, in fluorapatite by comparing the photoluminescence (PL) emission spectral features with that of in analogous La3+ based fluorapatite. The fluorapatites, NaCa3Bi0.95Eu0.05(PO 4)3F and NaCa3La0.95Eu 0.05(PO4)3F, were synthesized by conventional high temperature solid state reaction method and characterized by powder X-ray diffraction (XRD) and FT-IR spectroscopy. The Eu3+ PL results revealed a difference in the emission spectral features in NaCa 3Bi0.95Eu0.05(PO4)3F and NaCa3La0.95Eu0.05(PO4)3F. This difference in Eu3+ PL emission can be attributed to the difference in its site occupancy in the studied fluorapatites. © 2014 Elsevier Ltd.

The phosphor LaInO3:Eu3+ exhibits, in addition to the weak orange-red emission of Eu3+, a broad blue emission whose origin formed the basis for the reinvestigation of luminescence of LaInO 3 and the analogous LaGaO3, well known host lattices for luminescent centers. The results are analyzed based on the luminescence observed for In3+ and Ga3+ in various host lattices. An attempt is made to understand the mechanism of the luminescence of d 10 ions In3+ and Ga3+. © 2005 Elsevier Ltd. All rights reserved.

Luminescence of Eu2+ in Sr2SiO4:Eu2+, RE3+ [RE = Ce, Nd, Sm and Dy] phosphors was studied with a view to obtain an afterglow phosphor. The synthesized phosphors were characterized by powder X-ray diffraction (XRD), diffuse reflectance, photo- and thermoluminescence spectroscopic techniques. Afterglow was observed only with Dy3+ co-doped phosphor. The observed afterglow with Dy3+ co-doping originated from the formation of suitable traps which was supported by thermoluminescence results. © 2007 Elsevier Ltd. All rights reserved.

Sn doping in an n-type transparent conducting oxide MgIn2O4 is carried out and its effect on the high temperature transport properties viz. thermopower and electrical resistivity is studied. A solid solution exists in the composition window Mg1+xIn2-2xSnxO4 for 0 < x ≤ 0.4. The band gap as well as the transport properties increases with increasing Sn concentration. The high temperature resistivity properties indicate degenerate semiconducting behavior for all the compositions. The highest figure of merit obtained is 0.12 × 10-4 K-1 for the parent compound at 600 K. © 2010.