Ferroelectric phase transition in the whitlockite-type Ca9Fe(PO4)7; crystal structure of the paraelectric phase at 923 K

Synthesis and characterization of phosphates in molten systems Cs2O–P2O5–CaO–MIII2O3 (MIII—Al, Fe, Cr)

“…In compounds with general composition Ca 9 M III (PO 4 ) 7 [29][30][31][32] decreasing a and c parameters occurs with decreasing three valent metal's ionic radii. From Li to Cs sequence simultaneously increasing of a and decreasing c is observed in M I Ca 10 (PO 4 ) 7 phosphates.…”

Structural study and physical properties of a new phosphate KCuFe(PO4)2

“…Ca 9 R(PO 4 ) 7 also possess ferroelectric (FE) phase transitions [8]. Sr-analogs of such phosphates, Sr 9 R(PO 4 ) 7 have been shown to have a centrosymmetric monoclinically distorted b-Ca 3 (PO 4 ) 2 -type structure [9]. This compound exhibits an antiferroelectric (AFE) phase transition at 773 K [10].…”

Electrical Properties of Ca9ZnLi(PO4)7 Ceramics Prepared by Reactive Pressureless Sintering

“…16 Lazoryak et al 17 have reported this kind of phase transition in Ca 9 Fe(PO 4 ) 7 (at 890 ± 10 K) with the whitlockite-type crystal structure. The dielectric measurements reveal the ferroelectric nature of the phase transition.…”

“…The dielectric measurements reveal the ferroelectric nature of the phase transition. 17 In Ca 3 (VO 4 ) 2 -LaVO 4 cation conductors, partial La 3+ substitution in Ca 3Àx La 2x/3 (VO 4 ) 2 (0 £ x £ 1) (whitlockite-like structure) noticeably reduces the temperature of the polymorphic transition. 18 So, it can be speculated that, when Zn 2+ and Li + ions are doped into b-Ca 3 (PO 4 ) 2 , the phase-transition temperature (710 ± 10 K) could also be reduced.…”