Study of the Phase Transition in BaSm₂Mn₂O₇

Abstract

The existence of phase transition in BaSm 2 Mn 2 O 7 was revealed by high temperature X-ray diffractometry to be near 520 K. The phase transition is largely affected by the oxygen nonstoichiometry of this compound. For stoichiometric composition this phase has an orthorhombic distortion due to Jahn-Teller effect of Mn 3+ ion and is transformed into a tetragonal phase above the transition temperature. Structure of the high temperature phase is isotypic with that of the oxygen nonstoichiometric phase at room temperature; the latter has a Sr 3 Ti 2 O 7 -type crystal structure with double perovskite bloc.