Elasticity and anharmonicity of potassium chloride at high temperature

High temperature elasticity of single crystal potassium chloride has been studied by the Rectangular Parallelepiped Resonance (RPR) method up to 870 K (? 3.8 times the Debye temperature, ?). The elastic stiffness moduli, C ₁₁ and C ₄₄, decrease linearly with temperature while C ₁₂ increases slightly with temperature. The RPR method is particularly suited to measurements of elasticity at high temperatures, since no glues (which decompose at high temperature) are used to connect the transducers to a specimen. As a consequence, the measured spectrum closely approximates the theoretical spectrum of a specimen freely suspended in space with no external contact. The present elasticity data permits the investigation of the thermodynamic properties of potassium chloride far above the Debye temperature when used together with the previous zero-pressure data on thermal expansivity and heat capacity. The equation of state of potassium chloride is virtually unaffected by anharmonicity, even at T/?=3.8. One result is that the thermal pressure for KCl above the Debye temperature linearly increases with temperature. There is also small dependence on volume, in contrast to NaCl where there is no dependence on volume.