In situ Transmission Electron Microscopy Observation of Multiple Phase Transition in BaGd2Mn2O7

Abstract

In situ transmission electron microscopy observation revealed that BaGd2Mn2O7 undergoes several phase transitions upon heating. The orthorhombic Pnnm phase (I) at room temperature was transformed into a tetragonal P42/mnm (II) at around 420 K via an intermediate phase. On further heating, the other phase (III) nucleated in the phase II matrix at 623 K and grew until covering the whole inspected region by 723 K. Phase III has a 1.5% lattice mismatch along c compared with phase II, and presumably has a monoclinic symmetry. The transition between II and III was of the first order.