The lattice parameter of magnesiowfistite (Mgo.6Feo.~)O has been measured up to a pressure of 30 GPa and a temperature of 800 K, using an external heated diamond anvil cell and diffraction using X-rays from a synchrotron source. The experiments were conducted under quasi-hydrostatic condition, using neon as a pressure transmitting medium. The experimental P-V-T data were fitted to a thermal-pressure model with the isothermal bulk modulus at room temperature Kro = 157 GPa, (•Kro/OP)T=4, (~KT/OT),: -2.7(3) • 10 .2 GPa/K, (~KT/OT),= -0.2(2)x 10 -2 GPa/K, and the Anderson-Grfineisen parameter 6T=4.3(5)above the Debye temperature. The data were also fitted to the Mie-Griineisen thermal equation of state. The least-squares fit yields the Debye temperature 0Do =500(20) K, the Griineisen parameter 7o= 1.50(5), and the volume dependence q = 1.1 (5). Both thermal-pressure models give consistent P-V--T relations for magnesiowfistite to 140 GPa and 4000 K. The P-V-T relations for magnesiowiistite were also calculate by using a modified high-temperature Birch-Murnaghan equation of state with a 6T of 4.3. The results are consistent with those calculated by using the thermal-pressure model and the Mie-Griineisen relation to 140 GPa and 3000 K.

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Energy-dispersive x-ray diffraction experiments were carried out to investigate the structure of phase transitions under high pressure. It was found that the zinc blende (B3) to rock salt (B1) phase transition pressures of Zn0.93Mn0.07Se and Zn0.76Mn0.24Se bulk crystals are found 11.8±1.5 and 9.9±0.5 GPa, respectively. The respective bulk moduli are 61.8±0.8 and 60.5±0.8 GPa. The pressure-induced zinc blende (ZB) to rock salt (RS) structure phase transition is interpreted as a signature of the semiconductor to metal transition for Zn1−xMnxSe. The above interpretation is further corroborated by the observation of the disappearance of the longitudinal optical phonon at the pressure where the ZB to RS structure transition occurs.