X-ray studies of barium manganite Ba6Mn24O48 in the magnetic transition region

Abstract

X-ray studies of polycrystalline and pressure compacted barium manganite powder Ba6Mn24O48 were conducted at room and low temperatures. It was found that the compacting process that leads to the accumulation of macro- and microstress in the sample exerts a substantial amount of influence on the diffraction pattern. We obtained data for the temperature dependence of the lattice parameters a and c, as well as the linear thermal expansion coefficient in the basal plane of the tetragonal phase at temperatures 20–100 K. In the region of the magnetic phase transition temperature 45 K, we found an abnormal change in lattice parameter a and negative values for the linear thermal expansion coefficients αa. However, at the same time there were no singularities along the c(T) dependence. We suggest that one possible reason for this temperature behavior of the structural and thermal characteristics of barium manganite, is the significant anisotropy of the crystal lattice.