Effects of the synergy of pressure regulation and europium substitution on the microstructure and thermoelectric properties of Type-I clathrates EuxBa8−xCu6Si16Ge24

Abstract

The effects of the synergy of pressure regulation and Eu substitution on the microstructure and thermoelectric (TE) properties are investigated for type-I clathrates Eu[Formula: see text]Ba[Formula: see text]Cu6Si[Formula: see text]Ge[Formula: see text] ([Formula: see text], 0.5, 1, 1.5). The rare-earth-substituted and high-pressure modulated samples show complicated morphologies composed of abundant grains and rich in lattice defects. The Seebeck coefficient and the electrical conductivity of the rare-earth-substituted samples synthesized by HPHT method are consistent with [Formula: see text]-type conduction and metal-like behavior. The carrier concentration increases and the Hall carrier mobility decreases with increasing Eu substitution at room temperature. Although the increase of Eu filling rate decreased the Seebeck coefficient of the samples, it increased the power factor (PF) of the samples significantly. The thermal conductivity also reduced on account of Eu filling. As a result, a minimum [Formula: see text] value (0.67 Wm[Formula: see text]K[Formula: see text]) and a relatively higher zT value (0.68) are achieved. Compared to the Eu-free sample, the achieved zT value of the Eu-substituted sample is a [Formula: see text][Formula: see text]62% enhancement. So, high-pressure technique is an effective route to synthesize clathrate materials and optimize TE properties simultaneously.