INVESTIGATION OF THE CRYSTAL AND MAGNETIC-STRUCTURE OF THE PEROVSKITE SYSTEM SR2FETIO6-Y BY MOSSBAUER-SPECTROSCOPY AND NEUTRON-DIFFRACTION

The crystal structure of the cubic perovskite Sr2FeTiO5.81 has been refined in space group Pm3BARm using neutron powder diffraction data collected at 2 K. There is no evidence tor long-range magnetic order. Mossbauer and magnetic susceptibility data show a phase transition in the vicinity of 20 K which has been interpreted in terms of spin-glass behaviour. The long-range structural disorder of the B-site cations, and the mixed oxidation states of the iron (shown to be Fe3+ and Fe4+) lead to incompatible superexchange interactions and frustration of the spin system in establishing long-range order.