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

✍ Scribed by V.A. Morozov; A.A. Belik; S.Yu. Stefanovich; V.V. Grebenev; O.I. Lebedev; G. Van Tendeloo; B.I. Lazoryak

• Book ID: 102975032
• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 653 KB
• Volume: 165
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9521

✦ Synopsis

The double phosphate Ca 9 In(PO 4 ) 7 was obtained by solidstate reaction and was studied by room and high-temperature Xray powder diffraction, electron diffraction, high-resolution electron microscopy, second-harmonic generation (SHG) technique, differential scanning calorimetry, dielectric and conductivity measurements. The b-Ca 9 In(PO 4 ) 7 room-temperature phase is related to the mineral whitlockite and is similar to b-Ca 3 (PO 4 ) 2 . It has space group R 3 3c, with unit cell parameters: a = 10.4008(1) A ˚, c = 37.272(1) A ˚, Z = 6. The structure was refined by the Rietveld method (R wp = 4.69, R I = 1.81). A reversible first-order b2b 0 phase transition of the ferroelectric type with T c = 902 K is revealed by SHG, differential scanning calorimetry and dielectric measurements. The centrosymmetric b 0 -Ca 9 In(PO 4 ) 7 (973 K) has space group R 3 3c, a = 10.4611(2) A ˚, c = 37.874 (1) A ˚(R wp = 4.27, R I = 4.11). Compared to the low-temperature b-Ca 9 In(PO 4 ) 7 structure, b 0 -Ca 9 In(PO 4 ) 7 can be described as an orientational disordering of the P1O 4 tetrahedra together with a calcium disordering on the M3 site. # 2002 Elsevier Science (USA)