Cation Size Variance Effects in High-Tolerance Factor Ln0.7M0.3MnO3 Perovskites

series of five Ln0.7M0.3MnO3 perovskites (Ln=trivalent lanthanide; M=divalent alkaline earth) has been prepared. These have the same mean A-cation site radius of 1.26 ? (equivalent to a perovskite tolerance factor of 0.98) but varying amounts of Acation size disparity quantified by the size variance sigma2. As this increases, the temperatures of the metal–insulator and Curie transitions show a strong linear decrease but that of the structural transition between rhombohedral R c and orthorhombic Imma phases increases. Extrapolation from these and previous data indicates that the maximum metal–insulator temperature for an Ln0.7M0.3MnO3 perovskite is ~550 K. Different methods for estimating the Curie temperature are compared.