One-step ultra-rapid fabrication and thermoelectric properties of Cu2Se bulk thermoelectric material.

Cu2Se is a promising material for high temperature thermoelectric energy conversion due to its unique combination of excellent electronic properties and low thermal conductivity owing to its ionic liquid characteristics at high temperature. In this paper, fully dense single-phase bulk Cu2Se material was prepared by the combination of self-propagating high-temperature synthesis (SHS) with in situ quick pressing (QP) for the first time. This new approach shortens the duration of the synthesis from days to hours compared to conventional preparation methods. SHS-QP technique is an ultra-fast preparation method, which utilizes the heat released by the SHS reaction and an external applied pressure to achieve the synthesis and densification of materials in one-step. The ultra-fast process of the SHS-QP technique enables the fabrication of single-phase Cu2Se bulk materials with relative density of over 98% and with precise control over the stoichiometry owing to the ability to suppress the Se vapor during the reaction. The SHS-QP prepared Cu2Se samples exhibit excellent thermoelectric figure of merit, ZT ∼ 1.5 at 900 K, which is comparable to those of Cu2Se materials prepared by conventional methods. This study opens a new avenue for the ultra-fast and low-cost fabrication of Cu2Se thermoelectric materials.

Ultrafast Synthesis and Thermoelectric Properties of Mn1+ xTe Compounds.

MnTe compounds show great potential for thermoelectric applications in the intermediate temperature range (500-800 K) because of their large Seebeck coefficient and intrinsically low thermal conductivity. So far, the existing methods for the synthesis of MnTe compounds remain constrained to multistep processes that are time- and energy-intensive. Herein, we demonstrate ultrafast synthesis of high-density bulk MnTe compounds using a combination of self-propagating high-temperature synthesis (SHS) and plasma activated sintering. The entire synthesis and processing procedure takes less than 1 h. The thermodynamic consideration suggests that the SHS process includes two steps: (1) Mn + 2Te → MnTe2 + Q1 and (2) MnTe2 → MnTe + Te. With the heat released by step (1), the process moved in cycle and finished in a rather short time. The effect of extra Mn content on the structure and thermoelectric properties was investigated. There is some solubility limit of extra Mn in the Mn1+ xTe compound. The extra Mn occupy interstitial sites, leading to a decrease of carrier concentration while enhancing Seebeck coefficient and decreasing thermal conductivity. Low-temperature heat capacity data indicates that the Mn1.06Te compound has a high effective mass of 8.34 m0 and a low Debye temperature of 186 K, which are beneficial for the large Seebeck coefficient and low thermal conductivity. Therefore, the maximum ZT value reaches 0.57 at 850 K for the Mn1.06Te compound.

Ag3.5Bi7.5S13, a new member (N = 8) of the homologous series [Bi2S3]2.AgBiS2]((N-1)/2).

The silver bismuth tridecasulfide Ag3.5Bi7.5S13 crystallizes in the monoclinic space group C2/m. Its structure is built up of two alternating kinds of layered modules parallel to (001). In the module denoted A, octahedra around the metal positions (M = Ag/Bi, M2 and an S atom on 2/m, other atoms on m) alternate with paired monocapped trigonal prisms around Bi. The NaCl-type module B is composed of parallel eight-membered chains of edge-sharing octahedra running diagonally across it. Ag3.5Bi7.5S13 is the member with N = 8 of the pavonite homologous series (N)P of ternary compounds with the general formula [Bi2S3]2.[AgBiS2]((N-1)/2).