Gj. Fischer et al., ELASTICITY OF CATIO3, SRTIO3 AND BATIO3 PEROVSKITES UP TO 3.0 GPA - THE EFFECT OF CRYSTALLOGRAPHIC STRUCTURE, Physics and chemistry of minerals, 20(2), 1993, pp. 97-103
Elasticity of CaTiO3, SrTiO3 and BaTiO3 perovskites has been experimen
tally investigated as a function of pressure up to 3.0 GPa in a liquid
-medium piston cylinder apparatus using a high precision ultrasonic in
terferometric technique. Specimens used are hot-pressed fine-grained (
3-10 mum) polycrystalline aggregates with low porosity (< 1.5%). Compr
essional and shear wave velocities and their pressure derivatives have
been measured. The results are compared with previous studies on othe
r perovskites and the role of structural transitions is examined. We f
ind that the role of Ti-O6 PolYhedral tilting (such as observed in CaT
iO3) is small in the sense that a single well-defined general trend ex
ists in perovskites with a wide range of tilting angles, although ther
e is suggestion that cubic perovskites have slightly higher bulk modul
us than orthorhombic perovskites. In contrast, cation-anion displaceme
nt that changes crystal symmetry from cubic to tetragonal in BaTiO3 ha
s very large effects on elasticity. This distortion significantly redu
ces the bulk modulus (but not much the shear modulus) and results in a
n unusually large pressure derivative of bulk modulus (dK/dP approxima
tely 10). A large change in elasticity in BaTiO3 associated with the s
tructural transition (without a significant volume change) is a clear
example of the breakdown of the Birch's law between densities and elas
tic wave velocities.