Strong anisotropic thermal expansion in cristobalite-type BPO4

In this communication, the thermal expansion behavior of Cristobalite-type BPO4, determined from high-temperature X-ray diffraction studies, is being reported. BPO4 Crystallizes in tetragonal lattice, with space group I-4 (No. 82) at room temperature, with unit cell parameters: a=4.3447(2), c=6.6415(5)Angstrom and V=125.37(1)Angstrom(3). The tetragonal unit cell parameters at 900 degreesC are: a=4.3939(2), c=6.6539(6)Angstrom and V=128.46(1)Angstrom(3). The results show a very strong anisotropic expansion in the lattice, with the typical thermal expansion coefficients along a- and c-axis 12.9 x 10(-6) and 2.1 X 10(-6)/degreesC, respectively. The volume thermal expansion coefficient of the lattice is 28.2 x 10(-6)/degreesC in the temperature range of 25-900 degreesC. The variation of the crystal structure with temperature and the thermal expansion behavior are explained in this manuscript. The role of inter-polyhedral angle on the thermal expansion behavior has also been established. (C) 2004 Elsevier Inc. All rights reserved.