Tuning of phonon anharmonicity in pyrochlore titanates: temperature-dependent Raman studies of Sm2Ti2-xZrxO7 (x=0, 1/2, 3/4, and 2)and stuffed spin-ice Ho2+xTi2-xO7-x/2 (x=0, 1/3, and 2/3)

Anomalous temperature dependence of Raman phonon wavenumbers attributed to phononphonon anharmonic interactions has been studied in two different families of pyrochlore titanates. We bring out the role of the ionic size of titanium and the inherent vacancies of pyrochlore in these anomalies by studying the effect of replacement of Ti4?+ by Zr4?+ in Sm2Ti2O7 and by stuffing Ho3?+ in place of Ti4?+ in Ho2Ti2O7 with appropriate oxygen stoichiometry. Our results show that an increase in the concentration of the larger ion, i.e. Zr4?+ or Ho3?+, reduces the phonon anomalies, thus implying a decrease in the phononphonon anharmonic interactions. In addition, we find signatures of coupling between a phonon and crystal field transition in Sm2Ti2O7, manifested as an unusual increase in the phonon intensity with increasing temperature. Copyright (c) 2011 John Wiley & Sons, Ltd.

Ligational behaviour of (E)-2-amino-N ` -1-(2-hydroxyphenyl) ethylidene]benzohydrazide towards later 3d metal ions: X-ray crystal structure of nickel(IV) complex

Ligational behaviour of (E)-2-amino-N'-1-(2-hydroxyphenyl)ethylidene]benzohydrazide (Aheb) towards later 3d metal ionscopper(II), cobalt(II), manganese(II), zinc(II), cadmium(II) and nickel(IV)] has been studied. Their structures have been elucidated on the basis of spectral (IR, H-1 NMR, UV-Vis, EPR and FAB-mass), elemental analyses, conductance measurements, magnetic moments, and thermal studies. During complexation Ni(II) ion has got oxidized to Ni(IV). The changes in the bond parameters of the ligand on complexation has been discussed by comparing the crystal structure of the ligand with that of its Ni(IV) complex. The X-ray single crystal analysis of Ni(aheb)(2)]Cl-2 center dot 4H(2)O has confirmed an octahedral geometry around the metal ion. EPR spectra of the Cu(II) complex in polycrystalline state at room (300 K) and liquid nitrogen temperature (77 K) were recorded and their salient features are reported. (C) 2014 Elsevier B.V. All rights reserved.