Elastic anomalies in minerals due to structural phase transitions
Elastic anomalies in minerals due to structural phase transitions (in Phase transitions in minerals; strain and elasticity, Anonymous)
European Journal of Mineralogy (August 1998) 10 (4): 693-812
Landau theory provides a formal basis for predicting the variations of elastic constants associated with phase transitions in minerals. These elastic constants can show substantial anomalies as a transition point is approached from either the high-symmetry side or the low-symmetry side. In the limiting case of proper ferroelastic behaviour, individual elastic constants, or some symmetry-adapted combination of them, can become very small if not actually go to zero. In this second review article, selected examples of 'ideal' behaviour for different driving order parameter, coupling behaviour and thermodynamic character are set out in full, with a level of detail intended to permit the important sequence of steps to be followed in each case. Anomalies in the elastic properties on a macroscopic scale can also be understood in terms of the properties of acoustic phonons. These microscopic processes must be considered if elastic anomalies due to dynamical effects are to be accounted for correctly. Albite is considered to provide a likely example of proper ferroelasticity in minerals, and values for the required coefficients, extracted from experimental data, yield a complete picture of the expected elastic properties. The beta  alpha transition in quartz provides an example of co-elastic behaviour. Data for other compounds, including paratellurite and some with the perovskite-type structure, are reviewed to illustrate the full range of elastic anomalies to be expected at structural phase transitions in minerals.