Elasticity of Leucite Through High-Temperature Phase Transitions
CALIFORNIA UNIV LOS ANGELES
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A mean-field Landau-type model predicts that in some crystals certain elastic moduli experience significant softening in the neighborhood of phase transitions. Experimental verification of the influence of structural phase transitions on elastic moduli are needed to build a complete physical model and to predict the elastic behavior of minerals that undergo structural phase transitions. At ambient pressure and temperature, leucite KAlSi6O6 is tetragonal, but undergoes two structural transitions at about 870 and 900 K to a high-temperature cubic phase. We used resonant ultrasound spectroscopy RUS to monitor the resonant modes of leucite KAlSi6O6 from room temperature to 1500 K. In the stability field of cubic leucite, the five lowest resonant modes were measured from 900 to 1500 K. These five modes are predominantly shear vibrations, thus constrain the shear moduli, but not the compressional moduli. We find that C44 increases gradually from 19.33 GPa to 26.57 as temperature increases from 950 K to 1500 K. This behavior in C44 demonstrates the influence that phase transitions have on elastic properties at temperatures well removed from the transition temperature.