A comparison of the Ca3(PO4)2 and CaSiO3 systems, with a new structure refinement of tuite synthesized at 15 GPa and 1300  C

Abstract

Tuite, the high-pressure γ-form of the Ca 3 (PO 4 ) 2 system, has been synthesized from chlorapatite at 15 GPa and 1300 °C using a multi-anvil apparatus. Its crystal structure was determined with single-crystal X-ray diffraction. It is isostructural with palmierite, with space group R3m and unit-cell parameters a = 5.2522(9) and c = 18.690(3) Å. The structure of tuite is characterized by three distinct polyhedra, PO 4 , Ca1O 12 , and Ca2O 10 , that are translationally interconnected in the sequence of PO 4 -Ca2O 10 -Ca1O 12 -Ca2O 10 -PO 4 along the c axis.Comparison of the CaSiO 3 and Ca 3 (PO 4 ) 2 polymorphic systems shows a striking resemblance in the evolution of atomic packing arrangements as the polymorphic density increases. In both cases, the Ca atoms are progressively incorporated into the (Ca+O) close-packed monolayers, consistent with the hypothesis that close packing is a consequence of volume decrease as density increases. Based on this observation, we predict a possible high-pressure post-tuite phase.

Raman spectroscopy of various phosphate minerals and occurrence of tuite in the Elga IIE iron meteorite

“…Raman spectra of tuite are very consistent with the previous report, and all major bands can be recognized . The detailed crystal structure was determined only for Ca 3 (PO4) 2 ‐compositions, which belongs to palmierite‐type structures with R‐3 m space group . [PO4] tetrahedra occupy equivalent positions with slightly distorted P‐O distances.…”

“…Summary of experimental data on phosphate transformations at high pressures. Apatite‐F and apatite‐OH to tuite transition are from Murayama et al P‐peridotite, phosphorus‐bearing peridotite system; X‐02, synthesis of tuite in Ca 3 (PO 4 ) 2 system; and X‐13, synthesis of tuite from apatite‐Cl . The boundary of coesite (coes) to stishovite (st) transition is shown for comparison (see text).…”

An occurrence of tuite, γ‐Ca3(PO4)2, partly transformed from Ca‐phosphates in the Suizhou meteorite

“…, ; Thompson et al. ). Hence, the study of phosphate minerals and their high‐pressure polymorphs in heavily shocked meteorites has important implications because of the importance and prevalence of phosphate minerals within the solar system, and particularly because they are an indicator of shock conditions.…”

Photoluminescence properties of γ-Ca3(PO4)2:Sm3+ prepared under high-pressure and high-temperature conditions

“…Powder X-ray diffraction c-TCP crystallizes in a rhombohedral structure with the space group R-3 m (No. 166) [19,30]. Phosphorus atom is tetrahedrally coordinated by oxygen atoms.…”