Anomalous temperature dependence of the electric field gradient at the Y site in In0.1Y0.9Ba2Cu3O9- delta : Evidence for soft vibrational modes.

Abstract

Perturbed angular correlation (PAC) spectroscopy has been used to measure a well-defined static electric quadrupole interaction in a superconducting ceramic, ${\mathrm{In}}_{0.1}{\mathrm{Y}}_{0.9}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{9\ensuremath{-}\ensuremath{\delta}}$. Perturbation functions, Fourier transforms, and the derived PAC parameters are given for data taken at temperatures ranging from 77 to 1070 K. Indirect evidence is presented for the occupation of the Y site by the $^{111}\mathrm{In}$-$^{111}\mathrm{Cd}$ PAC probe. The derived electric field gradients were found to increase linearly with temperature. This result suggests the presence of soft, anisotropic vibrations in the structure. Additional evidence is presented to indicate that ${\mathrm{O}}^{2\ensuremath{-}}$-ion or O-vacancy transport may not occur in the Y coordination sphere.