Journal
PHYSICAL REVIEW B
Volume 80, Issue 18, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.80.184302
Keywords
band structure; bonds (chemical); Debye temperature; lanthanum alloys; neutron diffraction; phonons; specific heat; tellurium alloys; vacancies (crystal)
Funding
- Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. DOE. High-temperature
- U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy
- NSF [DMR- 0520547.]
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The phonon density of states (DOS) of La3-xTe4 compounds (x=0.0,0.18,0.32) was measured at 300, 520, and 780 K, using inelastic neutron scattering. A significant stiffening of the phonon DOS and a large broadening of features were observed upon introduction of vacancies on La sites (increasing x). Heat-capacity measurements were performed at temperatures 1.85 < T < 1200 K and were analyzed to quantify the contributions of phonons and electrons. The Debye temperature and the electronic coefficient of heat capacity determined from these measurements are consistent with the neutron-scattering results, and with previously reported first-principles calculations. Our results indicate that La vacancies in La3-xTe4 strongly scatter phonons and this source of scattering appears to be independent of temperature. The stiffening of the phonon DOS induced by the introduction of vacancies is explained in terms of the electronic structure and the change in bonding character. The temperature dependence of the phonon DOS is captured satisfactorily by the quasiharmonic approximation.
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