Poster: Temperature dependent structural studies of beta-pyrochlore KOs2O6 single crystals
Authors: Götz Schuck, Janusz Karpinski, Zbigniew Bukowski, Dmitry ChernyshovConference: Jahrestagung der Deutsche Gesellschaft für Kristallographie 2007, March 5-9, Bremen, Germany , PDF
The discovery of superconductivity in ß-pyrochlore oxides AOs2O6 (A = Cs, Rb and K) has recently attracted considerable interest. In particular profound influence of broken spatial inversion symmetry on the nature of pair-breaking in KOs2O6 was discussed [1]. We have studied the temperature dependent structural properties (100K - 400K) of the superconducting compound ß-pyrochlore KOs2O6 using synchrotron radiation at the BM1A beamline at ESRF. The KOs2O6 crystals have metallic conductivity and show a sharp transition to the superconducting state at Tc = 9.65 K. So far crystallographic data is available only at room temperature. The structure at room temperature is cubic with non-centrosymmetric space group F-43m [2]. A strong anisotropic character of the potassium channels was observed. Compared to the hypothetical ideal ß-pyrochlore lattice (Fd-3m), both osmium tetrahedral and oxygen octahedral network exhibit strong breathing mode like volume changes. We have shown that reflections that are forbidden in the ideal pyrochlore space group symmetry Fd-3m must be taken into consideration for the ß-pyrochlore compounds [2]. One main task was to study the evolution with temperature of these “forbidden” Bragg intensities in order to elucidate the influence of the observed Bragg peak intensity changes on the anisotropic character of the crystal structure of ß-pyrochlore KOs2O6.