A new transition metal diphosphide α-MoP₂ synthesized by a high-temperature and high-pressure technique

Abstract

A monoclinic α-MoP2, with the OsGe2-type structure (space group: C2/m, Z = 4) and lattice parameters a = 8.7248(11) Å, b = 3.2322(4) Å, c = 7.4724(9) Å, and β = 119.263°, was synthesized under a pressure of 4 GPa and at the temperature between 1100 ℃ and 1200 ℃ . The structure of α-MoP2 and its relation with other transition metal diphosphides are discussed. Surprisingly, the ambient pressure phase orthorhombic β-MoP2 (space group: Cmc21) is denser in structure than that of α-MoP2. Room temperature high-pressure X-ray diffraction studies exclude the possibility for phase transition from the β-MoP2 to α-MoP2, suggesting that the α-MoP2 is a stable phase at ambient conditions, which is also supported by the total energy and phonon calculations.