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A Raman spectroscopic study of the phase transition of BaZr(PO4)2: Evidence for a trigonal structure of the high-temperature polymorph |
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| Authors: | Thorsten Geisler Karin Popa Rudy JM Konings |
| Institution: | a Institut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstr. 24, 48149 Münster, Germany b European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, 76125 Karlsruhe, Germany c “Al.I. Cuza” University, Department of Inorganic and Analytical Chemistry, 11-Carol I Blvd., 700506 Iasi, Romania d Faculté des Sciences-Université de Nantes, Institut des Matériaux Jean Rouxel-Laboratoire de Chimie des Solides 2, rue de la Houssinière, B.P. 32229, 44322 Nantes Cedex 3, France |
| Abstract: | We have studied the structural evolution of monoclinic BaZr(PO4)2 during heating up to 835 K by Raman spectroscopy. In agreement with previous studies we found a first-order phase transition at about 730 K during heating while upon cooling the reverse transition occurs at 705 K. However, some disagreement about the crystal structure of the high-temperature polymorph occurs in the literature. While the space group has not yet been determined, the X-ray diffraction pattern of the high-temperature phase has been indexed on either an orthorhombic or a hexagonal unit cell. We found that the number of Raman active internal PO4 vibrational modes decrease from nine to six during the transition. A group theoretical survey through all orthorhombic, trigonal, and hexagonal factor groups revealed that the observed number of vibrations would only be consistent with the Ba and Zr atoms located at a  site, the P and two O atoms at a C3v(3m), and six O atoms at a Cs(m) site in the D3d factor group. Based on our Raman data, the space group of the high-temperature polymorph is thus either  ,  , or  . |
| Keywords: | Barium zirconium phosphate BaZr(PO4)2 Raman spectroscopy Phase transition |
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