RESUMO
In the present study, we have investigated the stability of different Ba-Si clathrates with pressure and temperature using DFT calculations and studied the stability of type I Ba8Si46 and type IX Ba24Si100 clathrates using high pressureâhigh temperature synthesis technique, calorimetry, and diffraction experiments. When increasing pressure, the type I Ba8Si46 clathrate and BaSi6 become more stable. In good qualitative agreement with experiments, the type IX Ba24Si100 clathrate becomes stable at a pressure of 1-2 GPa thanks to the pressure and thermal effect of both electronic and vibrational contributions. One can notice that the presence of Ba in the cages of type IX clathrate increases significantly the stability and the mechanical properties of type IX clathrate. We have determined the P-T existence domain of type IX Ba24Si100 clathrate from ex situ experiments, which was confirmed by in situ synchrotron X-ray experiments. At room pressure and under an oxidizing atmosphere, the type I Ba8Si46 and the type IX Ba24Si100 clathrates are stable up to about 560 °C and up to about 600 °C, respectively. The thermoelectric properties of type IX Ba24Si100 are also reported.
RESUMO
We report the lattice dynamics and thermoelectric properties of topological semimetal Ba3Si4. The lattice dynamics has been studied by Raman and inelastic neutron scattering experiments. Good agreement has been found with first-principles calculations. The presence of low-energy optical modes at about 7 meV mainly due to the heavy mass of the Ba atoms suggests a propensity to low thermal conductivity, which is favorable for thermoelectric applications. Our density functional theory calculations indicate that the semimetallic nature of Ba3Si4 is the origin for the rather large thermopower. Ba3Si4 shows high potential for a thermoelectric material with a Seebeck coefficient as large as -120 µV K-1 for 0.2 electrons/formula units through the substitution of Ba by appropriate cations, such as Y.