Crystal chemistry and polymorphism of potassium-magnesium monophosphate

摘要

The new compound KMgPO4 has been synthesized, and its structure has been determined at room-temperature (alpha form): space group is P2(1)/c (No. 14) with cell parameters a = 8.549(2) Angstrom, b = 5.078(1) Angstrom, c = 18.996(2) Angstrom, beta = 91.68(1)degrees, and Z = 8. Phase transitions occur at 362 and 422 degrees C, beta-KMgPO4 and gamma-KMgPO4 are orthorhombic, respectively Pna2(1) (No. 33) and Pnma (No. 62), The beta and gamma forms are related to the tridymite type, with a skeleton made of MgO4 and PO4 tetrahedra, but in a form, half of the magnesium atoms are pentacoordinated. (C) 1998 Academic Press. [References: 18]