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

Abstract

Structural changes in a series of 30% hole-doped $A{\mathrm{MnO}}_3$ perovskites have been studied by powder neutron diffraction. Large local changes, consistent with the freezing of Jahn-Teller distortions of the ${\mathrm{MnO}}_6$ octahedra, occur at the metal-insulator transition at $T_m=363\mathrm{}$ K in ${(\mathrm{L}\mathrm{a}}_{0.70}{\mathrm{Ca}}_{0.11}{\mathrm{Sr}}_{0.19}){\mathrm{MnO}}_3.$ 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 ${\mathrm{MnO}}_6$ octahedra. The decrease in $T_m$ across this series may reflect these increasing distortions which lower the local strain contribution to the transition enthalpy.