Phase stability of the layered oxide, Ca2Mn3O8; probing interlayer shearing at high pressure

Abstract

We have performed high-pressure neutron diffraction studies on the layered oxide, Ca₂Mn₃O₈. Studies up to approximately 6 GPa at temperatures of 120 and 290 K demonstrate that there are no structural phase transitions within this pressure range. Fits of the unit-cell volume to a Birch-Murngahan equation of state gives values for the bulk modulus of 137(2) GPa and 130(2) GPa at temperatures of 290 K and 120 K respectively possibly suggesting that Ca₂Mn₃O₈ is more compressible at lower temperature. Furthermore, compression along the principal axes are anisotropic on the local scale. Comparison of individual bond lengths and bond angle environments further demonstrate that compression is complex and likely results in a shearing of the layers.