Structural, transport, and thermal properties of single crystalline type-VIII clathrate Ba8Ga16Sn30

TL;DR

This study investigates the electrical, thermal, and structural properties of single crystalline Ba8Ga16Sn30 type-VIII clathrate, revealing low thermal conductivity and high thermoelectric potential due to local Ba atom vibrations.

Contribution

It provides detailed measurements and analysis of transport and vibrational properties of Ba8Ga16Sn30, highlighting the role of local Ba vibrations in thermal conductivity reduction.

Findings

Negative Seebeck and Hall coefficients indicate electron-dominated transport.

High Seebeck coefficient of 243 μV/K at 550 K suggests good thermoelectric potential.

Low thermal conductivity of 1.1 W/m·K at 150 K due to Ba atom vibrations.

Abstract

We report the electrical resistivity, Hall coefficient, thermoelectric power, specific heat, and thermal conductivity on single crystals of the type-VIII clathrate Ba8Ga16Sn30 grown from Sn-flux. Negative S and R_H over a wide temperature range indicate that electrons dominate electrical transport properties. Both rho(T) and S(T) show typical behavior of a heavily doped semiconductor. The absolute value of S increases monotonically to 243 uV/K with increasing temperature up to 550 K. The large S may originate from the low carrier concentration n=3.7x10^19 cm^(-3). Hall mobility u_H shows a maximum of 62 cm^2/Vs around 70 K. The analysis of temperature dependence of u_H suggests a crossover of dominant scattering mechanism from ionized impurity to acoustic phonon scattering with increasing temperature. The existence of local vibration modes of Ba atoms in cages composed of Ga and Sn atoms is evidenced by analysis of experimental data of structural refinement and specific heat, which give an Einstein temperature of 50 K and a Debye temperature of 200 K. This local vibration of Ba atoms should be responsible for the low thermal conductivity (1.1 W/m K at 150 K). The potential of type-VIII clathrate compounds for thermoelectric application is discussed.