Approaching the minimum lattice thermal conductivity of p-type SnTe thermoelectric materials by Sb and Mg alloying

SnTe, as the nontoxic analogue to high-performance PbTe thermoelectric material, has captured the worldwide interest recently. Many triumphant instances focus on the strategies of band convergence, resonant doping, and nano-precipitates phonon scattering. Herein, the p-type SnTe-based materials Sn0.85-xSb0.15MgxTe (x=0-0.10) are fabricated and a combined effect of Sb and Mg is investigated. Sb alloying tunes the hole carrier concentration of SnTe and decreases the lattice thermal conductivity. Mg alloying leads to a nearly hundredfold rise of disorder parameter due to the large mass and strain fluctuations, and as a consequence the lattice thermal conductivity decreases further down to ~0.64Wm^-1K^-1 at 773K, close to the theoretical minimum of the lattice thermal conductivity (~0.50Wm^-1K^-1) of SnTe. In conjunction with the enhancement of the Seebeck coefficient caused by band convergence due to Mg alloying, the maximum zTmax reaches ~1.02 and the device zTdevice of ~0.50 at 773K for Sn0.79Sb0.15Mg0.06Te, suggesting this SnTe-based composition has a promising potential in intermediate temperature thermoelectric applications.

Anisotropic thermoelectric properties of layered compound SnSe2

Similar to high performance SnSe thermoelectrics, SnSe2 is also a layered structured semiconductor.However, its anisotropic thermoelectric properties are less experimentally investigated. In this work,Cl-doped SnSe2 bulk materials are successfully prepared, and their thermal stability and anisotropic transport properties are systematically studied. Unexpectedly, different from the theoretical prediction and other typical layered thermoelectric compounds like Bi_2Te_3, the out-of-plane zT_c value is higher than in-plane zT_a for the same composition. The zT value is significantly enhanced by Cl doping. A maximum zT_c of ~0.4 at 673 K is achieved in SnSe_(1.88)Cl_(0.12), twice higher than previously reported Cl-doped SnSe_2 synthesized by the solvothermal method.

Low contact resistivity and long-term thermal stability of Nb0.8Ti0.2FeSb/Ti thermoelectric junction

Although half-Heusler compounds are quite promising for thermoelectric power generation,there is only limited research on the interfacial structure between metal electrode and half-Heusler compounds for device applications.This work reports on the characteristics of Nb0.8Ti0.2Fe Sb/Ti junction and its evolution behavior during 973 K.The Nb0.8Ti0.2Fe Sb/Ti interface consists of one Ti0.9Fe0.1 layer and one Fe-poor layer.There is an Ohmic contact and a low contact resistivity(0.15μΩcm^-2)in this junction,on account of the matching of working functions between Nb0.8Ti0.2Fe Sb and Ti0.9Fe0.1 interlayer.The high doping of Ti high carrier concentration in Nb Fe Sb matrix leads to a high carrier concentration,which results in inducing a large tunneling current at this interface.After aging treatment at 973 K,the Fe-poor layer and the Ti0.9 Fe0.1 layer continues to expand,resulting in the increase of the thickness of the interfacial layer and the contact resistivity.The interfacial electrical is only 1.9μcm^-2 after 25 days’aging.The thickness of the interface layer has a good linear relation with the square root of aging time,which firmly indicates that the growth of the layer is determined by mutual diffusion of Fe and Ti atoms across the interface.The low contract resistivity and long-time thermal stability demonstrate the great potential of Nb0.8Ti0.2Fe Sb/Ti thermoelectric junction in high efficiency half-Heusler TE devices.