Comparative Transmission and Emission Mössbauer Studies on Various Perovskite-Related Systems

A whole group of compounds which have the ABO3 stoichiometry and meet the appropriate conditions on the ratio of ionic sizes and metal-oxygen bond lengths is named after the well known mineral, perovskite (CaTiO3). The basic structure is cubic as depicted in Fig. 1. The stability of this structure depends on the cations occupying the A and B sites. Variation of the cations at these sites produces an astonishingly wide variety of magnetic and electric properties [1]. For example, the originally dielectric CaTiO3 becomes a ferroelectric material when Ca is substituted by Ba. Partial substitution of Ti by Zr, with Pb at the A site results in a piezoelectric substance. (Ba,La)TiO3 is a semiconductor, while a wide range of cuprates like YBa2Cu3O7-d shows high temperature superconductivity. One of the hottest topic in perovskite chemistry and physics today is the colossal magnetoresistance effect which is found for example in (La,Sr)MnO3, (La,Sr)(Fe,Co)O3 and other compounds (although the perovskite structure is not a precondition for the CMR effect).