Elastic Moduli and Thermal Expansion of Lutetium Single Crystals from 4.2 to 300°K

The adiabatic elastic moduli of hexagonal close-packed lutetium single crystals have been determined by the ultrasonic pulse superposition technique over the temperature range 4.2–300°K. The values at 300°K in units of 1011 dyn/cm2 are C11=8.62, C33=8.09, C44=2.68, C66=2.71, and C13=2.8; the values extrapolated to 0°K are C11=9.10, C33=8.40, C44=2.91, C66=2.96, and C13=2.9. The Debye temperature calculated using the elastic moduli at 0°K is 184.5°K. The bulk elastic properties have also been calculated and they agree favorably with previously predicted polycrystalline values. The linear thermal-expansion coefficients of the lutetium single crystals have been determined over the same temperature range by using a linear-variable-differential-transformer dilatometer. The room-temperature coefficients of thermal expansion are α∥=2.0×10−6 and α⊥=4.82×10−6°K−1. A maximum in α⊥ was found at 130°K, which apparently correlates with the maximum found in the γ⊥/γ∥ ratio at 130°K, where γ is the Grüneisen constant.