A Raman Spectroscopic Study of the Phase Transistion of BaZr(PO4)2 - Evidence for a Triginal Structure of the High-temperature Polymorph.

We have studied the structural evolution of monoclinic BaZr(PO4)2 during heating up to 835K by Raman spectroscopy. In agreement with previous studies we found a first-order phase transition at about 730K 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 D3d ð¯3mÞ 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.

GEISLER T.;  POPA Karin;  KONINGS Rudy;  POPA A.F.; 

2006-05-31

ELSEVIER SCI LTD

JRC33556

https://publications.jrc.ec.europa.eu/repository/handle/JRC33556,   

10.1016/j.jssc.2006.01.065,