Abstract
In this research, a method combining the mechanical alloying with the vacuum sintering or hot pressing was adopted to obtain the compact of β-Zn4Sb3. Pure zinc and antimony powders were used as the starting material for mechanical alloying. These powders were mixed in the stoichiometry ratio of 4 to 3, or more Zn-rich. Single phase Zn4Sb3 was produced using a nominally 0.6 at. % Zn rich powder. Thermoelectric Zn4Sb3 bulk specimens have been fabricated by vacuum sintering or hot pressing of mechanically alloyed powders at various temperatures from 373 to 673 K. For the bulk specimens sintering at high temperature, phase transformation of β-Zn4Sb3 to ZnSb and Sb was observed due to Zn vaporization. However, single-phase Zn4Sb3 bulk specimens with 97.87% of theoretical density were successfully produced by vacuum hot pressing at 473 K. Electric resistivity, Seebeck coefficient, and thermal conductivity were evaluated for the hot pressed specimens from room temperature to 673 K. The results indicate that the Zn4Sb3 shows an intrinsic p-type behavior. The increase of Zn4Sb3 phase ratio can increase Seebeck coefficient but decrease electric conductivity. The maximum power factor and figure of merit (ZT) value were 1.31 × 10−3 W/mK2 and 0.81 at 600 K, respectively. The ZT value was lower than that reported in the available data for materials prepared by conventional melt growth and hot pressed methods, but higher than the samples fabricated by vacuum melting and heat treatment techniques.
Highlights
Thermoelectric (TE) materials that convert electrical energy into heat can be used to manufacture thermoelectric generators or thermoelectric coolers
The as-milled powder, sintered, and hot-pressed specimens were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM)
It can be noted that only the Zn4 Sb3 with 0.6 at. % of excess Zn exhibited nearly a single β-Zn4 Sb3 phase, this composition was used for the subsequent vacuum sintering and hot pressing
Summary
Thermoelectric (TE) materials that convert electrical energy into heat can be used to manufacture thermoelectric generators or thermoelectric coolers. Energies 2018, 11, 1200 of up to 200,000 h Despite these numerous advantages, thermoelectric materials are expensive and their efficiency is smaller than 5%, far less than conventional refrigerators or generators. Many new compounds and alloys have been proposed, including skutterudites, clathrates, half-Heusler alloys, Zn4 Sb3 , SnSe, GeTe, and AgSbTe2 and some layer-structured compounds [9,10,11,12,13,14,15] These new materials exhibit higher ZT values at high temperature ranges. The high defect densities in mechanically alloyed powders are expected to reduce the material’s lattice thermal conductivity, improving the efficiency of thermoelectric conversion [20]. The feasibility to prepare a single β-phase Zn4 Sb3 thermoelectric material with a high ZT value was investigated in the present study where bulk Zn4 Sb3 alloy was fabricated by combining mechanical alloying with a vacuum sintering or vacuum hot pressing approach
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