High-Temperature Phase Transition in the Whitlockite-Type Phosphate Ca9In(PO4)7

Microstructures of phosphatic porcelain from sintering to vitrification: Evidence from sherds excavated in Charleston, South Carolina

“…This excess Ca was evidently taken up by subsolidus plagioclase crystals as they developed reverse zoning (Figure 5), as well as by the melt phase, and thence liquidus anorthite microlites (Figures 4d, 4e). The phosphate in these two samples is thus inferred to have been transformed into a different whitlockite-like mineral, of which several are known in both natural and synthetic systems (e.g., Morozov et al, 2002;Kara & Stevens, 2003;Hughes, Jolliff, & Rakovan, 2008). Merrillite [Ca 18 Mg 2 (PO 4 ) 14 ] is one candidate; it also has a CaO/P 2 O 5 (MP) ratio of 2.7 but it contains about twice the amount of magnesia (3.8% MgO) as the phosphate in CSP-2 and CSP-8.…”

Whitlockite-Related Phosphates Sr9A(PO4)7 (A=Sc, Cr, Fe, Ga, and In): Structure Refinement of Sr9In(PO4)7 with Synchrotron X-Ray Powder Diffraction Data

“…Ferroelectric phase transitions have recently been found in Ca 9 A(PO 4 ) 7 (A=Fe and In) (24,25). Low-temperature forms of Ca 9 A(PO 4 ) 7 crystallize in space group R3c with lattice parameters of aE10:3 ( A and cE37:3 ( A (Z=6) in a similar way to b-Ca 3 (PO 4 ) 2 (8,9,24,25).…”

“…Low-temperature forms of Ca 9 A(PO 4 ) 7 crystallize in space group R3c with lattice parameters of aE10:3 ( A and cE37:3 ( A (Z=6) in a similar way to b-Ca 3 (PO 4 ) 2 (8,9,24,25). In Ca 9 A(PO 4 ) 7 , the Ca1-Ca3 sites are occupied by Ca 2+ ions, the M4 and M6 sites are vacant, and the M5 site is occupied by A 3+ ions.…”

“…In Ca 9 A(PO 4 ) 7 , the Ca1-Ca3 sites are occupied by Ca 2+ ions, the M4 and M6 sites are vacant, and the M5 site is occupied by A 3+ ions. High-temperature forms of Ca 9 A(PO 4 ) 7 belong to space group R % 3c; having lattice parameters of aE10:5 ( A and cE37:9 ( A (24,25). In Ca 9 Fe(PO 4 ) 7 , reversible redox reactions occur without destroying its crystal structure (8,26).…”

“…The replacement of Ca 2+ ions in synthetic whitlockite, Ca 18 Mg 2 H 2 (PO 4 ) 14 (22) (8,9,24,25) are replaced by Sr 2+ ions. We have found these Sr compounds to have complicated superstructures with lattice parameters of aE18:0 ( A, bE10:7 ( A, cE18:4 ( A, and bE1331 (Z ¼ 4).…”