Elastic Constants of LiF from 4.2°K to 300°K by Ultrasonic Methods

The values of the elastic constants of LiF at 4.2^∘{}K are found to be c₁₁=12.46×10¹¹, c₄₄=6.49×10¹¹, and c₁₂=4.24×10¹¹ dynes/cm². At 300^∘{}K c₁₁=11.12×10¹¹, c₄₄=6.28×10¹¹, and c₁₂=4.20×10¹¹ dynes/cm². A Debye characteristic temperature, θD, has been calculated from these values by using the Houston method of averaging the velocity over different directions in the crystal. At 4.2^∘{}K, θD=734^∘K in good agreement with the specific heat work of Martin. At 300^∘{}K, θD=708^∘K which is not in good agreement with values derived from specific heat measurements. A model has been suggested in which a combination of Debye and Einstein terms is used in the specific heat theory.