Nagel, L. J. and Fultz, B. and Robertson, J. L. and Spooner, S. (1997) Vibrational entropy and microstructural effects on the thermodynamics of partially disordered and ordered Ni3V. Physical Review B, 55 (5). pp. 2903-2911. ISSN 0163-1829. http://resolver.caltech.edu/CaltechAUTHORS:NAGprb97
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Samples of Ni3V were prepared with two microstructures: (1) with equilibrium D022 order, and (2) with partial disorder (having a large D022 chemical order parameter, but without the tetragonality of the unit cell). For both materials, we measured the difference in their heat capacities from 60 to 325 K, inelastic neutron-scattering spectra at four values of Q at 11 and at 300 K, and Young's moduli and coefficients of thermal expansion. The difference in heat capacity at low temperatures was consistent with a harmonic model using the phonon density of states (DOS) curves determined from the inelastic neutron-scattering spectra. In contrast, at temperatures greater than 160 K the difference in heat capacity did not approach zero, as expected of harmonic behavior. The temperature dependence of the phonon DOS can be used to approximately account for the anharmonic contributions to the differential heat capacity. We also argue that some of the anharmonic behavior should originate with a microstructural contribution to the heat capacity involving anisotropic thermal contractions of the D022 structure. We estimate the difference in vibrational entropy between partially disordered and ordered Ni3V to be Spdis -Sord =(+0.038±0.015)kB /atom at 300 K.
|Additional Information:||© 1996 The American Physical Society Received 14 February 1996; revised manuscript received 13 June 1996 We thank M. Walter and G. Ravichandran for providing the ultrasonic facilities for the attempted sound velocity measurements, and R. D. Conner for help with the mechanical testing. L. Preister and I. Wong performed much of the sample preparation. We thank L. Anthony for valuable discussions. The Oak Ridge National Laboratory is managed for the Department of Energy by Lockheed Martin Energy Research, Oak Ridge, Tennessee under Contract No. DE-AC05-96OR22464. This work was supported by the U.S. Department of Energy under Contract No. DE-FG-03-96ER45572.|
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