Low-temperature thermophysical and crystallographic properties of BaZrO3 perovskite

摘要

The temperature dependence of the crystallographic and thermoelastic properties of BaZrO3 perovskite in the temperature range 4.2 K and 450 K has been investigated using high-resolution time-of-flight neutron powder diffraction and literature values of the isobaric heat capacity. At all measured temperatures, BaZrO3 is cubic, space group Pm3 over bar m, with no clear evidence for diffuse scattering at critical points of the primitive cubic Brillouin zone. Simultaneous fitting of the temperature dependences of the isochoric heat capacity and unit cell volume showed the thermophysical properties of BaZrO3 were consistent with a two-term Debye model in which the cations and anions behave independently of one another with Debye temperatures of 220(2) K and 730(5) K, respectively. This model is further consistent with the temperature variations of the atomic displacement parameters fitted to a modified Debye model in which the vibrational Debye temperatures of the anion are significantly larger than those associated with the cations. The evolution of the crystallographic parameters of BaZrO3 is compared to those of BaCeO3, for barium in the cavity site, and SrZrO3, for zirconium in the octahedral site.