Magnetic order, transport and infrared optical properties in the A CrO 3 system ( A = Ca, Sr, and Pb)

The crystal structure and magnetic structure of the chromate series ACrO3 (A = Ca, Sr, Pb) where Cr exhibits the unusual Cr 4+ oxidation state have been studied by comprehensive diffraction experiments. In addition we present a detailed analysis of the infrared optical properties of polycrystalline CaCrO3 which is found to be metallic along all crystallographic directions. CaCrO3 forms the rare case of a three-dimensional antiferromagnetic and metallic transition-metal oxide in which the occurrence of magnetic ordering is closely coupled to a flattening of the lattice. The same C-type magnetic order is also found in the Sr material and again is coupled to a structural distortion associated with lattice flattening. However, in SrCrO3 only a part of the sample transforms into the antiferromagnetic distorted phase. In contrast to CaCrO3 and SrCrO3 ,P bCrO 3 clearly is insulating with a significantly larger unit-cell volume and exhibits G-type magnetic order.