Heat capacity and microstructure of ordered and disordered Pd3V

Differences in the heat capacity and thermal expansion of cubic (fcc-disord ered) and tetragonal (DO22-ordered) Pd3V were measured from 40 K to 315 K. Below 100 K the heat capacity difference was consistent with harmonic vibra tions. At higher temperatures, however, the data show significant anharmoni c effects. Measurements of elastic constants, densities and thermal expansi on showed that the anharmonic volume expansion contribution (C-p - C-V) cou ld account for only about one-third of this anharmonic heat capacity differ ence. The remainder may originate with elastic and plastic deformation of t he polycrystalline microstructure. Strain energy from anisotropic thermal c ontractions of grains in the tetragonal ordered phase contributes to the he at capacity, but some of this strain energy is eliminated by plastic deform ation. The vibrational entropy difference of disordered and ordered Pd3V wa s estimated to be S-dis - S-ord = (+0.035 +/- 0.001)k(B)/atom at 300 K, wit h 70% of this coming from anharmonic effects.