Six-fold-coordinated phosphorus by oxygen in AlPO4 quartz homeotype under high pressure.
AlPO4 belongs to the berlinite quartz homeotype family, which has been the subject of intense high-pressure research triggered by the supposed existence of reversible pressure-induced amorphization. X-ray diffraction experiments, complemented with ab initio calculations, demonstrate the existence of two high-pressure crystalline polymorphs and show that AlPO4 shares the same two-stage densification mechanism as silica. In the first step, a compact hexagonal sublattice of oxygen atoms is formed. In the second step, the cations redistribute in the interstices giving rise to a monoclinic distorted CaCl2 phase. The most outstanding feature of the phase is that phosphorous becomes six-fold coordinated by oxygen, adopting a configuration unknown so far in solid-state science. This finding opens possibilities in the high-pressure chemistry of phosphorus. The close relationship of AlPO4 with silica suggests the existence of completely unexplored families of compounds analogous to those of six-fold-coordinated silicates but based on PO6.
ICMUV, Universidad de Valencia, c/Dr. Moliner 50, 46100 Burjassot, Valencia, Spain. Julio.Pellicer@uv.es
Julio
J
Pellicer-Porres
Antonino Marco
AM
Saitta
Alain
A
Polian
Jean Paul
JP
Itié
Michael
M
Hanfland