Cation disorder and the metal-insulator transition temperature in manganese oxide perovskites

Structural changes in a series of 30% hole-doped AMnO₃ perovskites have been studied by powder neutron diffraction. Large local changes, consistent with the freezing of Jahn-Teller distortions of the MnO₆ octahedra, occur at the metal-insulator transition at Tₘ=363 K in (La0.70Ca0.11Sr0.19)MnO₃. The 4 K structures of four compositions with the same A-cation radius but increasing amounts of A-site disorder, show an increasing radial distortion of the MnO₆ octahedra. The decrease in Tₘ across this series may reflect these increasing distortions which lower the local strain contribution to the transition enthalpy.