A¹⁵⁵Gd Mossbauer study of GdBa₂Cu₃O_7-x: results concerning crystal structure and dynamics

Abstract

Two samples of the compound GdBa2Cu3O7-x, one with x approximately 0 (Tc=93.5 K) and one with x>0.5 (Tc<1.8 K), have been studied by 155Gd Mossbauer spectroscopy in the temperature range 1.5 K<or=T<or=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 the authors' 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.