A GD-155 MOSSBAUER STUDY OF GDBA2CU3O7-X - RESULTS CONCERNING CRYSTAL-STRUCTURE AND DYNAMICS

Two samples of the compound GdBa//2Cu//3O//7// minus //x, one with x approximately 0 (T//c equals 93. 5 K) and one with x greater than 0. 5 (T//c greater than 1. 8 K), have been studied by **1**5**5 Gd Moessbauer spectroscopy in the temperature range 1. 5 K less than equivalent to T less than equivalent to 120 K. A non-zero value of the asymmetry parameter eta in both samples shows the point symmetry at Gd sites to be orthorhombic at low temperatures. The narrow linewidth implies a high degree of perfection of our samples. Significant differences of the frequency spectra of Gd ions between the two samples are derived from the temperature dependence of the absorption cross sections and of the centre shifts.