Single crystal X-ray diffraction studies of Na2MnF5 at high hydrostatic pressures

Abstract

Abstract The crystal structure of Na2MnF5 has been investigated by high pressure single crystal and powder X-ray diffraction techniques. The unit cell parameters have been determined in the pressure range from ambient conditions to 2.93 GPa. The P21/c space group symmetry is retained in this pressure range. Above 3 GPa the single crystals collapse and a polycrystalline specimen is formed. Preliminary high pressure powder diffraction studies show that the transformation occurs in the range 3–4 GPa. The transition is reversed when the pressure is lowered. The structure of Na2MnF5 consists of parallel infinite chains of corner connected MnF6 octahedra that extend along [100]. The chains are held together via bonds to surrounding Na ions. A structure determination based on data collected at 2.34 GPa has been performed. With 199 observed independent reflection intensities, a simple structural model described by 31 parameters was refined to wR = 0.078 (R = 0.084). Major changes observed are decreased inter-chain distances, also reflected in significantly shortened Na–F distances for one of the Na atoms. The compressibility is smallest along the chain direction [100]. The isotropic bulk modulus B 0 obtained by fitting the relative volume changes to a Birch type equation of state is 48(4) GPa.