U.V. Varadaraju

Metal atom incorporation studies on the phases with NZP structure: □NbTiP3O12

Abstract A wide variety of electropositive elements of the periodic table can be inserted into the vacant sites in the host framework structure of hexagonal NbTiP 3 O 12 (an analog of nasicon) to give rise to isostructural phases. Synthesis, characterization, and preliminary data on the structure, IR spectra, and electrical resistivity are presented. Possible areas for further exploration are delineated.

Electrical and magnetic properties of pure and Li intercalated Bi1.7−xPbxV8O16 phases

Abstract Hollandite oxides of the type Bi 1.7− x Pb x V 8 O 16 have been synthesized. The electrical resistivity studies show that the conductivity improves upon Pb substitution. The feasibility of Li intercalation in the system has been established. Magnetic susceptibility studies on the pure and Li intercalated phases show that except for pure Bi 1.7 V 8 O 16 , all phases exhibit Pauli paramagnetism. No superconductivity is encountered down to 12 K in any of the phases.

Superconductivity studies on TlMBaCuO (M = Ce, Th, Pr, Tb, Pb, and Te) system☆

Superconductivity with a T{sub c,zero} at 75 {plus minus} 1 K has been observed in Tl-M-Ba-Cu-O (M = Ce, Th) system for a starting nominal composition of Tl{sub 2.2}M{sub 1}Ba{sub 2}Cu{sub 3}O{sub y}. X-ray data show that the compounds are multiphasic with the 2,201 phase as the predominant one which is responsible for superconductivity. Lower T{sub c} values are noted for M = Pr and Tb. Only metallic behavior is observed for pure Tl{sub 2}Ba{sub 2}Cu{sub 1}O{sub y} and M = Pb or (Pb + Sb) or Te containing phases down to 15 K.

Investigation of valence states in the perovskite oxides, LaAFeNbO6 (A=Ca, Sr)

Compounds of the type, LaAFeNbO(6) (A = Ca Sr) have been synthesized to study the electrical and magnetic properties and to examine valence degeneracy. The results show that valence degeneracy is not operative and the compounds are insulating. Magnetic susceptibility data show that part of the Fe is in Fs(2+) state, thus oxidizing part of Nb4+ to Nb5+ by an internal redox mechanism. The presence of mixed valent Fe is confirmed by Mossbauer spectra