Structure Cristalline de la Phase Haute Température et Haute Pression de Mg3(PO4)2

Solid-state synthesis and crystal growth of the high-temperature and high-pressure form of magnesium monophosphate, now referred as Mg3(PO4)2-III, were achieved at 22 kbar, 1000°C and followed by a complete crystallographic characterization. Mg3(PO4)2-III belongs to the triclinic space groupP1. Unit cell contains four formula groups, and crystal parameters are found to bea=8.512(2) Å;b=8.982(2) Å;c=9.320(3) Å;α=116.34(2)°;β=91.50(2)°;γ=114.49(2)°. The crystal structure may be described as nearly regular PO4tetrahedra sharing corners and edges with distorted MgO6and MgO5polyhedra. The dense structure is discussed and compared with those of other polymorphs, Mg3(PO4)2-I, i.e., farringtonite (cf.γ-Zn3(PO4)2) and Mg3(PO4)2-II, cf. sarcopside (i.e., olivine structure with ordered vacancies).