Novel Phase Transition in BaPr 2Mn 2O 7

Abstract

The rare earth manganite BaLn 2Mn 2O 7(Ln = rare earth element) has a Sr 3Ti 2O 7-type layered perovskite structure with double-block oxygen octahedra belonging to the Ruddlesden-Popper-type homologous series AO(ABO 3) 2. In Premanganite, a novel phase transition was first observed in situ at 1040 K by a thermal transmission electron microscope. At 1040 K, reflections began to split along the c-direction in the selected area diffraction pattern. This indicates that a new phase appears in the original phase matrix; the c length of the new phase is 1.5% longer than that of the original phase. After about 5 min, the original phase disappears. No change in the crystal symmetry (space group I41/ mmm) is observed above 1040 K.