| Thermoelectric (TE) materials can directly achieve conversion from heat energy to electricity and vice versa. TE generators and refrigerators, which are made of TE materials, are widely utilized in many filed, such as power generator in spaceflights. waste heat harvest and so on. GeTe-AgSbTe2 based TE materials possess high effective mass and high carrier mobility, and large Seebeck coefficient and low phonon thermal conductivity. It can be used as P leg in TE generator. It is generally recognized that permanent lattice strain in these compositions might lead to reduced thermal conductivity and enhanced TE performance. Recently, high TE performance and extremely low phonon thermal conductivity was obtained in PbTe-AgSbTe2 materials. which have similar chemical compositions with GeTe-AgSbTe2. The extremely low phonon thermal conductivity was attributed to the instinctively complex nanostructures in PbTe-AgSbTe2, which had been proved in theory and experiment. There are few researches on the microstructure in GeTe-AgSbTe2. In this present work, high performance of GeTe-AgSbTe2 materials were prepared through melting and liquid nitrogen quenching and melt spinning. The instinctive microstructures in GeTe-AgSbTe2 were studied through scanning electron microscope and transmission electron microscope. The relationship between microstructure and TE transport properties was discussed detailedly. TE properties of GeTe-AgSbTe2 were optimization through forming solid solution and varying Ag/Sb.(1). (GeTe)x(AgSbTe2)100-x(x= 75,80,85,90) bulk materials were prepared by a method combined liquid nitrogen quenching and hot pressing. The non-equilibrium solidification can make fine microstructures in bulk materials. Microstructures of bulk samples were observed through Transmission electron microscope. Many grains sized in 50-100 nm were present. Precipitated Ag-Sb riched nanodots sized 2-10 nm coherently embeds in the substrate. Some nanoscopic supercell regions distribute widely in bulk materials with coherent boundary. Those nanostructures can increase the interface density and scatter the long and mid wavelength phonons. The maximum ZT value reached 1.53 at 730 K.(2). (GeTe)x(AgSbTe2)100-x(x= 80,85) bulk materials were prepared and their TE properties were studied. The carrier concentration, electrical conductivity and thermal conductivity of samples change regularly as AgSbTe2 content increases. Phonon thermal conductivity of all samples is 0.9-1.0 Wm-1K-1 at room temperature, which is reduced by 60% compared with pure GeTe. The maximum ZT value of 1.5 was obtained at 723 K.(3). (GeTe)x(AgySb2-yTe3-y)100-x(x=80,85,90; y=0.5-1.4) bulk materials with in situ nanoscopic modulation structures and different Ag/Sb ratio were prepared and investigated. The nonhomogeneous composition might lead to the incommensurable modulation sized in 2-10 nm. There are 2-5% mismatch in crystal lattice between these modulations. Several kinds of interface such as small angle boundary, twin boundary and anti-phase boundary were observed throuthout the sample. The highly dense interface in bulk samples is beneficial to reduction of phonon thermal conductivity due to the nanosized interface is potential scattering mechanism for phonon transport. TE performance was improved by varying Ag/Sb ratio. The maximum ZT of 1.7 was obtained at 748 K.(4). (GeTe)x(AgySb2-yTe3-y)100-x(x=8O; y=0.5-1.4) with fine nanostructure were prepared by melt spinning (MS) and hot pressing. Lamellar structures with width 40-100 nm are observed in a large-scale field. There are two kinds of modulation structures with different periodicity of 3-5 nm and - 0.7 nm in micro structure. Supercell regions sized in tens of nanometers distribute widely throughout the samples. Highly dense edge dislocations have formed around the modulation structure. Those multiscale nanostructures can scatter long and mid wavelength phonon in a larger frequency coverage and reduce phonon thermal conductivity significantly. As expected, the measured thermal conductivity and phonon thermal conductivity of MSed samples have reduced by 20-30% compared with that of melt samples. TE performance of MSed sample has improved by 20%. The maximum ZT value of 1.7 was obtained at 723 K.(5). The stability of thermoelectric performance was initially studied. Sample prepared by melt spinning was annealed at 450℃for 100 hours, and the TE properties were compared with that of unannealed sample. Although electrical conductivity and total thermal conductivity increased after annealing, phonon thermal conductivity and ZT of annealed sample almost is the same as that of unannealed samples. This result indirectly proofs the stability of in situ nanostructure in melt spinning sample.
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