Pressure-temperature phase diagram and thermoelastic behavior of manganese fluoride up to 13.1 GPa and 700 K

Studying manganese fluoride (MnF2) under high-pressure and high-temperature (HP-HT) conditions is of great significance for understanding its important magnetic and piezomagnetic properties. The structural evolution and thermoelastic behavior of MnF2 were studied at HP-HT conditions up to similar to 13.1 GPa and similar to 700 K based on in situ synchrotron angle dispersive powder x-ray diffraction (XRD) combined with diamond anvil cell (DAC). Four phases of MnF2 are successfully observed through the pressure-temperature (P-T) range of the experiment. The structural phase transitions are with the following sequence: rutile-type (P4(2)/mnm) -> alpha-PbO2-type (Pbcn) -> P (4) over bar 2m -> ZrO2-type (Pbcm) -> SrI2-type (Pbca) at HP-HT conditions, where the alpha-PbO2-type (Pbcn) and the P (4) over bar 2m structures are observed upon decompression. A phase diagram of MnF2 is presented in this study. In addition, the bulk modulus for the SrI2-type structure (Pbca) of MnF2 is 84 (3) GPa when fixed K-0' = 4. Moreover, we also obtain (partial derivative K/partial derivative T)(P) = -0.012 (7) GPaK(-1), and the volumetric thermal expansion coefficient alpha(0) = 3.8 (7) x 10(-5) K-1 at 300 K. Furthermore, the thermal expansion coefficients for the rutile-type structure (P4(2)/mnm) of MnF2 by fitting the temperature-volume data to the Fei-type thermal equation of state (EoS) are also obtained. The volumetric thermal expansion coefficient of MnF2 is 0.87 x 10(-5) K-1, and its axial thermal expansivities are alpha(a0) = 0.13 x 10(-5) K-1 and alpha(c0) = 0.64 x 10(-5) K-1 along the a-axis and c-axis, respectively.