Electrical Resistivity and Scattering Mechanisms of GeTe-Rich Thermoelectric Materials in the System GeTe-AgBiTe2

The experimentally observed anomalies in temperature dependences of the Hall coefficients and the electrical resistivities for hot-pressed samples of Ge 1−x Ag x/2 Bi x/2 Te with 0.095 < x < 0.333, due to the ferroelectric lattice instabilities in the phase transition region, are discussed.The Landau-Lifschitz type criterion for these phenomena shows that the phase transition is of second order. According to the soft-mode conception the main part of the anomalous increase in the resistivity is due to the soft-TO phonon scattering and the curvature caused by the soft-TO phonon near zero wavevector is accelerated with increasing AgBiTe 2 content.

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“…The last behaviour is typical for a metals. It is established in [11] that at higher temperatures ρ begins to decrease as in semiconductors.…”

Section: Sample Preparation and Measurementsmentioning

confidence: 99%

Phase transition in Ge_1-xAg_x/2Bi_x/2Te solid solutions and related transport phenomena

Avramova¹,

Plachkova²

2000

J. Phys.: Condens. Matter

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“…As a Pb-free chalcogenide, GeTe-based material has been extensively studied as a high-performance intermediate temperature thermoelectric material. − At low temperatures, Ge atoms in r-GeTe tend to move away from the center of the octahedral structure along the [111] direction due to the presence of 4s 2 lone pair electrons, resulting in a distorted octahedral structural unit and a rhombohedral structure. − Upon heating, Ge atoms dynamically vibrate to the center of octahedral structure unit and GeTe undergoes a ferroelectric phase transition from the low-temperature rhombohedral structure to the high-temperature cubic structure at around 700 K . Moreover, the low-temperature rhombohedral GeTe structure usually deviates from its exact stoichiometry, resulting in a large number of intrinsic Ge vacancies.…”

Section: Introductionmentioning

confidence: 99%

Vacancy-Based Defect Regulation for High Thermoelectric Performance in Ge₉Sb₂Te_12–x Compounds

Chen

Bai

et al. 2020

ACS Appl. Mater. Interfaces

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Defect engineering is the core strategy for improving thermoelectric properties. Herein, cation doping along with modulation of cation vacancy has been developed in GeTebased materials as an effective method to induce vacancy-based defects to boost their thermoelectric performance. A series of ternary compounds of Ge 9 Sb 2 Te 12−x (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15) was prepared by vacuum-melting and annealing combined with the spark plasma sintering (SPS) process. The role of Sb doping and cation vacancy on thermoelectric properties was systematically investigated. It is found that alloying Sb 2 Te 3 into GeTe increases the concentration of cation vacancies, which is corroborated by both positron annihilation measurements and theoretical calculations. The vacancies, stacking faults, and planar defect interactions determine the thermoelectric transport properties. Adjusting the deficiency of Te effectively tunes the concentration of cation vacancies and dopant defects in the structure. In turn, this tunes the carrier concentration close to its optimum. A high power factor of 32.6 μW cm −1 K −2 is realized for Ge 9 Sb 2 Te 11.91 at 725 K. Moreover, large strains induced by the defect structures, including Sb dopant, vacancy, staking faults, as well as planar defects intensify phonon scattering, leading to a significant decrease in the thermal conductivity from 7.6 W m −1 K −1 for pristine GeTe to 1.18 W m −1 K −1 for Ge 9 Sb 2 Te 11.85 at room temperature. All of the above contribute to a high ZT value of 2.1 achieved for the Ge 9 Sb 2 Te 11.91 sample at 775 K.

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“…The materials which were synthesized in ampoules were powdered to grain sizes lower than 0.16 mm, after that they were pressed at 300 K and under 5000 kg/cm 2 pressure for 3 min. The process was repeated under the same pressure and time at the temperature 673 K. Then the materials were annealed in argon atmosphere for about 100 h at 773 K [10]. The present paper reviews the thermoelectric properties (S, s, j) of the hot-pressed samples from the system (GeTe) 1--x (AgBiTe 2 ) x with x ¼ 0.03, 0.10, 0.15, 0.20 in the temperature range from 300 to 800 K. The ZT values are evaluated.…”

Section: Preparation Of Samplesmentioning

confidence: 67%

Materials for Thermoelectric Application Based on the System GeTe-AgBiTe2

Plachkova

Avramova

2001

phys. stat. sol. (a)

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Subject classification: 72.20.Pa; S8.13; S8.15The thermoelectric parameters (thermoelectric power S, electrical conductivity s and thermal conductivity j) from the system (GeTe) 1--x (AgBiTe 2 ) x are measured in the temperature range from 300 to 800 K on hot-pressed samples with x ¼ 0.03, 0.10, 0.15, 0.20. The thermoelectric figure of merit Z and the Ioffe criterion ZT average are calculated. The maximum value ZT ¼ 1.32 at T ¼ 700 K is found for the composition containing 3 mol% AgBiTe 2 . This value is practically the same as for TAGS 85, a material widely applied in USA space devices, and determines the utility of the new thermoelectric material.

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Electrical Resistivity and Scattering Mechanisms of GeTe-Rich Thermoelectric Materials in the System GeTe-AgBiTe2

Cited by 8 publications

References 4 publications

Phase transition in Ge_1-xAg_x/2Bi_x/2Te solid solutions and related transport phenomena

Phase transition in Ge_1-xAg_x/2Bi_x/2Te solid solutions and related transport phenomena

Vacancy-Based Defect Regulation for High Thermoelectric Performance in Ge₉Sb₂Te_12–x Compounds

Materials for Thermoelectric Application Based on the System GeTe-AgBiTe2

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Electrical Resistivity and Scattering Mechanisms of GeTe-Rich Thermoelectric Materials in the System GeTe-AgBiTe2

Cited by 8 publications

References 4 publications

Phase transition in Ge1-xAgx/2Bix/2Te solid solutions and related transport phenomena

Phase transition in Ge1-xAgx/2Bix/2Te solid solutions and related transport phenomena

Vacancy-Based Defect Regulation for High Thermoelectric Performance in Ge9Sb2Te12–x Compounds

Materials for Thermoelectric Application Based on the System GeTe-AgBiTe2

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Product

Resources

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Phase transition in Ge_1-xAg_x/2Bi_x/2Te solid solutions and related transport phenomena

Phase transition in Ge_1-xAg_x/2Bi_x/2Te solid solutions and related transport phenomena

Vacancy-Based Defect Regulation for High Thermoelectric Performance in Ge₉Sb₂Te_12–x Compounds