Nature of the cubic to rhombohedral structural transformation in (AgSbTe2)15(GeTe)85 thermoelectric material

Abstract

The existence of a large thermoelectric figure of merit in (AgSbTe2)15(GeTe)85 has been known for many years. However, the nature of the crystallographic transformation in these materials from a high-temperature cubic to a low-temperature rhombohedral polymorph and its effect on electrical transport has not been clearly established. Transmission electron microscopy studies were performed that show extensive twinning in the low-temperature structure, resulting from lattice strain during the dilation along the (111) crystallographic direction. Analysis of differential scanning calorimetric studies indicates that the transformation is of second order, so that the high-temperature cubic phase is nonquenchable. High-temperature x-ray diffraction was performed to establish the transformation temperature, which was found to be complete upon heating at a temperature of 510K. Results of electrical conductivity measurements as a function of temperature on as-cast samples are discussed in terms of the observed twinning.

Impact of Coinage Metal Insertion on the Thermoelectric Properties of GeTe Solid-State Solutions

“…Other well established classes of high performance materials involving carrier and phonon engineering of GeTe are the so-called TAGS alloys with composition (GeTe) x (AgSbTe 2 ) 1-x exhibiting zT values of more than 1 [42][43][44][45] . Similar values of zT at mid-temperature ranges (600-800 K) were achieved for different Powder X-ray diffraction X-ray diffraction (XRD) patterns were recorded at room temperature in the 2θ range 15-120° with a step size of 0.026° and a scan time per step of 400 s using a PANalytical X'Pert Pro diffractometer (Cu K-L 2,3 radiation, λ = 1.5418 Å, PIXcel 1D detector).…”

Influence of nanoscale Ag2Te precipitates on the thermoelectric properties of the Sn doped P-type AgSbTe2 compound

“…Therefore, optimal TE materials must feature a high PF and low thermal conductivity. 1 (LAST) [18][19][20][21] and GeTe, called tellurium antimony germanium silver (TAGS) 22,23 and have successfully exhibited enhanced TE performance.…”

Microstructure And Thermoelectric Properties Of Tags-90 Compounds Fabricated By Mechanical Milling Process

“…The compositions focused GeTe rich compositions; and subsequently studied on TAGS-80, TAGS-85 and TAGS-90 due to higher ZT value [10]. On the other hand, Doping and structural change yielded negligible effect on the transport properties [11,12], but defects, nanoscale compositional modulations, nano domains, precipitate, twins, and grain boundaries showed remarkable effects [6,12,13]. As new approach, works based on defects can increase the Seebeck coefficient by enhancing scattering factor (g), and reducing thermal conductivity through enhanced phonon scattering, which serves as an effective way to improve the TE performance.…”

“…Many researchers have established TE materials such as Bi 2 Te 3 , Sb 2 Te 3 , SiGe, SnTe, TAGS and PbTe as the best performance materials for several decades, and these materials still continue to attract interest in TE research and industry [6]. Among these, the compound (GeTe) x (AgSbTe 2 ) 100−x , commonly called TAGS-x has been given much attention for power generation from waste heat [7,8], because of its maximum ZT generation in 300∼450 • C temperature range, which is temperature range of automobile's exhaust gases and industrial waste heat [9].…”