Structural, Magnetic, and Thermal Properties of La1−tCatCrO3−δ

A broad study on the properties of Ca-substituted LaCrO3is reported. Problems in the synthesis of Ca-rich samples of La1−tCatCrO3−δare addressed. For the La-rich region, synthesis in air provides La1−tCatCrO3with partial formation of CrIV. At reducing conditions, CrIVcan be converted to CrIII. The properties of oxidized and reduced samples are compared since differences are of importance for applications. The maximum reduction, without decomposition, corresponds ideally to δ =t/2, but this could not be fully achieved in 10% H2+ 90% N2at 1263 K. Unit cell data, atomic coordinates (from powder neutron diffraction data), thermal expansion, and magnetic property data are provided. The crystal structure is orthorhombic (GdFeO3-type) at 298 K; the rhomobohedral LaAlO3-type variant exists at high temperatures. Sample reduction influences slightly the orthorhombic distortion, increases the unit cell volume quite considerably, enhances the temperature domain of the orthorhombic versus the rhombohedral modification, and increases the magnetic moment and the antiferromagnetic ordering temperature. The microscopic thermal expansion is independent of the Ca content (0.00 ≤t≤ 0.30) and is slightly enhanced for the rhombohedral phase. The antiferromagneticGx-type ordering in LaCrO3is retained upon substitution. However, for oxidized samples, a smallerAzcomponent develops upon substitution, whereas for field cooled samples parasitic ferromagnetism appears. For fully reduced samples, the aliovalent Ca substitution implies unit cell compression and oxygen vacancy formation with modest effect on magnetic properties. The additional partial exchange of CrIII(d3) by CrIV(d2) for oxidized samples has significant impact on the magnetic properties.