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39 results on '"Rajarajan, A.K."'

24. X-ray photoelectron spectroscopic studies of the valence state of Tl in single-Tl-O-layered TlBa1-xSrxLaCuO5 (0_etix_eti1)

Author

Sundaresan, A., Gopinath, C.S., Tamhane, A.S., Rajarajan, A.K., Sharon, M., Subramanian, S., Pinto, R., Gupta, L.C., and Vijayaraghavan, R.

Abstract

The valence state of thallium in TlBa1-xSrxLaCuO5 (x=0.0, 0.4, 0.7, and 1.0) has been investigated by measuring Tl 4f core levels by x-ray photoelectron spectroscopy. It is shown that the valence state of Tl in TlBaLaCuO5 (nonsuperconducting) is 3+, whereas that in TlSrLaCuO5 (superconducting, Tc=32 K) is between 3+ and 1+. The origin of holes in the latter compound is discussed in terms of charge transfer between Tl ions and Cu-O layers as has been found in double-Tl-O-layered compounds. ? 1992 The American Physical Society.

Published
1992

37. Non-isovalent substitution of Ba2+in superconducting YBa2Cu3O7-y

Author

Rajarajan, A.K., Guptasarma, P., Palkar, V.R., Ayyub, P., Multani, M.S., Gupta, L.C., and Vijayaraghavan, R.

Abstract

We report the structural, magnetic and superconducting properties of YBa2−xMxCu3O7(M=La3+or K+). Single-phase compounds form over a wide range of x in YBa2−xMxCu3O7and up to x = 0.2 in YBa2−xMxCu3O7. A substituent concentration of 15% triggers an orthorhombic to tetragonal phase15 transition in both systems. In spite of the associated disorder in the Cu(1)-0(1) chains, such a transition does not affect Tcdrastically. Tcgets systematically depressed with increasing x. A temperature-dependent paramagnetic response is observed in YBa2−xMxCu3O7between 90 and 300K.

Published
1988
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39. Structural, chemical and magnetic investigations of polycrystalline Zn1− x Mn x O

Author

Deshmukh, Alka V., Patil, S.I., Yusuf, S.M., Rajarajan, A.K., and Lalla, N.P.

Subjects
*MOLECULAR structure, *MAGNETIC crystals, *POLYCRYSTALS, *ZINC compounds, *INORGANIC synthesis, *HIGH temperatures, *X-ray diffraction, *SOLID state chemistry
Abstract

Abstract: Present study reports the detailed structural and magnetic, as well as chemical analysis of polycrystalline Zn1− x Mn x O (where x=0, 0.005, 0.01, 0.03, 0.05 and 0.1) samples synthesized by the high-temperature solid state reaction route. X-ray diffraction studies reveal the presence of secondary phase for higher Mn-doping concentrations (x≥0.03). Secondary phase formation having spinel structure is confirmed and reported as an evidence for the first time using transmission electron microscopy study. Chemical investigations using X-ray photoelectron spectroscopy showed the presence of Mn in two valence states. From the observed results we are of the opinion that Zn2+ ions, mainly present at or near grain boundaries, diffuse into manganese oxide to form a stable spinel phase Zn x Mn3− x O4 at or near the grain boundaries of ZnO/Zn1− x Mn x O. Magnetization measurements did not show any magnetic transition down to 5K. [Copyright &y& Elsevier]

Published
2010
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