Low temperature orthorhombic to monoclinic transition due to size effect in Nd0.7Ca0.3-xSrxMnO3: Evidence for a new type of charge ordering

The structures of the perovskites Nd0.7Cr0.30-xSrxMnO3 have been determined at 293 and 1.7 K for x=0, 0.08, and 0.3. Ah these manganites, except the low-temperature form of Nd0.7Ca0.3MnO3 (x=0), exhibit the classical orthorhombic Pnma (GdFeO3) structure. For Nd0.7Ca0.3MnO3, a monoclinic structure, involving a new kind of charge ordering, is observed at 1.7 K. The importance of this phenomenon for the understanding of the CMR properties of these materials is emphasized. (C) 1996 Academic Press, Inc.