Heat capacity and microstructure of ordered and disordered Pd3V

Differences in the heat capacity and thermal expansion of cubic (fcc-disordered) and tetragonal (DO 22 -ordered) Pd 3 V were measured from 40 K to 315 K. Below 100 K the heat capacity difference was consistent with harmonie vibrations. At higher temperatures, however, the data show significant anharmonic effeets. Measurements of elastic constants. densities and thermal expansion showed that the anharmonic volume expansion contribution (C P - C V ) could account for only about one-third of this anharmonic heat capacity difference. The remainder may originate with elastic and plastic deformation of the polycrystalline microstructure. Strain energy from anisotropic thermal contractions of grains in the tetragonal ordered phase contributes to the heat capacity, but some of this strain energy is eliminated by plastic deformation. The vibrational entropy difference of disordered and ordered Pd 3 V was estimated to be S dis - S ord = (+0.035 ± 0.001)K B /atom at 300 K. with 70% of this coming from anharmonic effeets.