Phonon density of states and heat capacity ofLa3−xTe4

Abstract

The phonon density of states ͑DOS͒ of La 3−x Te 4 compounds ͑x = 0.0, 0.18, 0.32͒ 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 x͒. Heat-capacity measurements were performed at temperatures 1.85Յ T Յ 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 La 3−x Te 4 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.

High thermoelectric figure of merit in heavy hole dominated PbTe

“…All of the measurements were carried out under vacuum in the temperature range of 300-750 K. Consistent measurements, within $10% for Seebeck and resistivity, were confirmed at NASA's Jet Propulsion Laboratory (JPL) (using W-Nb thermocouples) and at ZTPlus Inc. using the ULVAC-ZEM3 system on a sample with zT $1.4 at 700 K. Scanning Seebeck coefficient measurements (at 300 K) on the sample with Hall carrier density of 9 Â 10 19 cm À3 showed a Seebeck coefficient variation of only 5 mV K À1 (full width for 90% of the data). Heat capacity (C p ) is estimated by C p (k B per atom) ¼ 3.07 + 4.7 Â 10 À4 Â (T/K-300), which is obtained by fitting the experimental data reported by Blachnik and Igel 34 within an uncertainty of 2% for all the lead chalcogenides at T > 300 K. It should be emphasized that this simple equation agrees well with the theoretical prediction 35 taking the lattice vibration (Debye temperature 5 of 130 K), dilation (bulk modulus 36 of 39.8 GPa, the linear coefficient 5 of thermal expansion of 20 Â 10 À6 K À1 ) and charge carriers contributions into account. At 700 K or above this equation gives C p $10% higher than the Dulong-Petit value.…”

Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials

“…C ph, H and C D are contribution of harmonic phonons and lattice dilation, which can be calculated by sound velocity, thermal expansion coefficient, and density. [60] Normal and shear ultrasonic measurements were performed at room temperature using input from a Panametrics 5052 pulser/ receiver with the filter at 0.03 MHz. The response was recorded via a Tektronix TDS5054B-NV digital oscilloscope.…”

Heavy-impurity resonance, hybridization, and phonon spectral functions inFe1−xMxSi (M=Ir, Delaire1, Al-Qasir2, May3 et al. 2015Phys. Rev. BSelf Cite392190View full textAdd to dashboardCite

“…This thermal behavior was contrasted with high-pressure measurements, which showed that, at constant temperature, the phonons behave quasiharmonically upon compression 30 . Related effects of doping and temperature on the electronic structure and phonons in transition metals were reported in [45][46][47] .…”