Crystal structure and phase transitions of strontium zirconium diorthophosphate, SrZr(PO4)2

Abstract

The crystal structure of SrZr(PO4)2 at 298K was determined from conventional X-ray powder diffraction data using direct methods, and it was further refined by the Rietveld method. The structure was triclinic (space group P1̄, Z=2) with a=0.77508(4)nm, b=0.78887(5)nm, c=0.51251(3)nm, α=95.754(3)°, β=90.228(2)°, γ=92.474(2)°, and V=0.31149(3)nm3. Final reliability indices were Rwp=8.51%, Rp=6.07%, and RB=2.46%. The powder specimens were also examined by high-temperature XRD and differential thermal analysis to reveal the occurrence of phase transitions from triclinic to monoclinic at 405K, then to hexagonal (or trigonal) at 1196K during heating. Upon cooling, the reverse change of the latter transition occurred at 1175K. The subsequent monoclinic-to-triclinic transition was martensitic and incomplete during further cooling to 298K. The monoclinic phase is most probably isostructural with yavapaiite. The present paper has described, for the first time, the higher- and lower-temperature polymorphs of the yavapaiite-type structure.