Phase transitions in Cd3P2 at high pressures and high temperatures

The high-pressure, high-temperature structural behaviour of Cd3P2 has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0 GPa in compression. The experimental zero-pressure bulk modulus of the low-pressure phase is 64.7(7) GPa, which agrees quite well with the calculated value of 66.3 GPa using the tight-binding linear muffin-tin orbital method within the local density approximation. Tentatively, the high-pressure phase has an orthorhombic crystal structure with space group Pmmn (#59). The relative volume change at the phase transition is ΔV/V = −5.5%. Amorphization of the sample occurs above 25 GPa. A P–T phase diagram of Cd3P2 has been constructed. A metastable phase is observed at ambient conditions after heating the sample to above 600 K at about 3 GPa. A hexagonal unit cell can describe the crystal structure of the metastable phase.