Zur Kristallchemie der B-Metalle

Schubert, K.; Fricke, Horst

doi:10.1515/ijmr-1953-441004

Cited by 9 publications

(6 citation statements)

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“…69 GeTe crystallizes in the low temperature α-phase (space group R3m) which can be described as a distorted NaCl-type structure and transforms into the parent structure type (β-phase, space group Fm3 ˉm) in the temperature range from 390 to 460 °C depending on the actual composition. 70,71 Abrikosov et al reported the solubility of Bi 2 Te 3 in GeTe to be about 5%. 72 For the low temperature phase vacancies lead to the formation of planar defects which have been frequently observed and were attributed to vacancy layers.…”

Section: Transport Properties In Dependence Of Temperature and Therma...mentioning

confidence: 99%

Thermoelectric efficiency of (1 − x)(GeTe) x(Bi₂Se_0.2Te_2.8) and implementation into highly performing thermoelectric power generators

et al. 2015

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Here we report for the first time on a complete simulation assisted "material to module" development of a high performance thermoelectric generator (TEG) based on the combination of a phase change material and established thermoelectrics yielding the compositions (1 - x)(GeTe) x(Bi(2)Se(0.2)Te(2.8)). For the generator design our approach for benchmarking thermoelectric materials is demonstrated which is not restricted to the determination of the intrinsically imprecise ZT value but includes the implementation of the material into a TEG. This approach is enabling a much more reliable benchmarking of thermoelectric materials for TEG application. Furthermore we analyzed the microstructure and performance close to in-operandi conditions for two different compositions in order to demonstrate the sensitivity of the material against processing and thermal cycling. For x = 0.038 the microstructure of the as-prepared material remains unchanged, consequently, excellent and stable thermoelectric performance as prerequisites for TEG production was obtained. For x = 0.063 we observed strain phenomena for the pristine state which are released by the formation of planar defects after thermal cycling. Consequently the thermoelectric performance degrades significantly. These findings highlight a complication for deriving the correlation of microstructure and properties of thermoelectric materials in general.

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Section: Transport Properties In Dependence Of Temperature and Therma...mentioning

confidence: 99%

Thermoelectric efficiency of (1 − x)(GeTe) x(Bi₂Se_0.2Te_2.8) and implementation into highly performing thermoelectric power generators

et al. 2015

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“…GeTe is a narrow band-gap semiconductor [3] and is ferroelectric at room temperature with a Curie temperature of about 705 K. The low temperature ferroelectric phase has a rhombohedraly distorted NaCl type crystal structure with the space group R3m [4][5][6][7][8]. Structural distortions involve relative displacement of the Ge and Te sublattices along the body cell diagonal and subsequent rhombohedral shear deformation along [111] direction which changes the rhombohedral angle from its fcc value of 60 • to α.…”

Section: Introductionmentioning

confidence: 99%

Anomalous temperature-induced volume contraction in GeTe

2015

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The recent surge of interest in phase change materials GeTe, Ge2Sb2Te5, and related compounds motivated us to revisit the structural phase transition in GeTe in more details than was done before. Rhombohedral-to-cubic ferroelectric phase transition in GeTe has been studied by high resolution neutron powder diffraction on a spallation neutron source. We determined the temperature dependence of the structural parameters in a wide temperature range extending from 309 to 973 K. Results of our studies clearly show an anomalous volume contraction of 0.6% at the phase transition from the rhombohedral to cubic phase. In order to better understand the phase transition and the associated anomalous volume decrease in GeTe we have performed phonon calculations based on the density functional theory. Results of the present investigations are also discussed with respect to the experimental data obtained for single crystals of GeTe.

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“…Therefore, varying the transition temperatures constitutes an intriguing aspect for optimizing the performance of GST bulk thermoelectrics by Se doping. Limitations are indicated by the fact that at ambient conditions GeSe crystallizes in a binary variant of the black phosphorus structure type while the structure of α-GeTe is a binary variant of the structure type of gray arsenic. − Even though at HT both compounds exhibit a rocksalt-type structure, the ternary phase diagrams Ge/Sb/Te and Ge/Sb/Se are significantly different. There is no homologous series of layered compounds “Ge n Sb 2 Se 3+ n ” corresponding to those on the pseudo-binary line Sb 2 Te 3 /GeTe.…”

Section: Introductionmentioning

confidence: 99%

Enhancing the Thermoelectric Properties of Germanium Antimony Tellurides by Substitution with Selenium in Compounds Ge_nSb₂(Te_1–xSe_x)_n+3 (0 ≤ x ≤ 0.5; n ≥ 7)

et al. 2014

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Quenched pseudocubic germanium antimony tellurides (GST compounds) exhibit promising thermoelectric properties. These are related to the nanostructures which can be influenced by varying the composition and the thermal treatment. The substitution of Te by Se in bulk samples of Ge n Sb 2 Te n+3 with high thermoelectric figures of merit (ZT) is possible over a wide compositional range. This results in solid solution series Ge n Sb 2 (Te 1−x Se x ) n+3 with 0 < x < 0.75 for n ≥ 7. Se substitution reduces the average lateral extension of the defect layers in quenched samples. This is a consequence of the reduced mobility during the quenching process due to the lower cubic to trigonal phase transition temperatures of Se-substituted samples. Most pronounced for n = 7, Se doping increases the transition temperatures between the nanostructured (pseudo)cubic modification of quenched samples and their layered trigonal phase. This increases the temperature ranges in which the materials can be employed without altering their nanostructures and properties. When Se is introduced, the Seebeck coefficient increases and the thermal conductivity decreases. The ZT value of Ge 7 Sb 2 Te 8 Se 2 , for instance, increases up to 1.2 at 425 °C, which is 6 times higher than that of Ge 7 Sb 2 Te 10 . Similarly, the ZT value of Ge 12 Sb 2 (Te 1−x Se x ) 15 increases up to a factor of 2 for x = 0.2 at temperatures below 400 °C. The most promising thermoelectric properties (ZT = 1.2 at 425 °C for n = 7 and ZT = 1.1 at 350 °C for n = 12) are observed for x = 0.2 whereas higher Se substitution rates result in a less pronounced effect. The average structures were determined by powder as well as single crystal X-ray diffraction (SCXRD). The real structure of quenched Ge n Sb 2 (Te 1−x Se x ) n+3 (0 ≤ x ≤ 0.5; n ≥ 7) bulk material was investigated by high-resolution electron microscopy (HRTEM) with respect to the degree of substitution (x) and correlated with the resulting changes of the thermoelectric properties. The decrease of the lateral extension of the defect layers with increasing Se content as found by HRTEM and electron diffraction is confirmed by SCXRD data for Ge ∼5 Sb 2 (Te 0.13 Se 0.87 ) ∼8.

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Zur Kristallchemie der B-Metalle

Cited by 9 publications

References 0 publications

Thermoelectric efficiency of (1 − x)(GeTe) x(Bi₂Se_0.2Te_2.8) and implementation into highly performing thermoelectric power generators

Thermoelectric efficiency of (1 − x)(GeTe) x(Bi₂Se_0.2Te_2.8) and implementation into highly performing thermoelectric power generators

Anomalous temperature-induced volume contraction in GeTe

Enhancing the Thermoelectric Properties of Germanium Antimony Tellurides by Substitution with Selenium in Compounds Ge_nSb₂(Te_1–xSe_x)_n+3 (0 ≤ x ≤ 0.5; n ≥ 7)

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Zur Kristallchemie der B-Metalle

Cited by 9 publications

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Thermoelectric efficiency of (1 − x)(GeTe) x(Bi2Se0.2Te2.8) and implementation into highly performing thermoelectric power generators

Thermoelectric efficiency of (1 − x)(GeTe) x(Bi2Se0.2Te2.8) and implementation into highly performing thermoelectric power generators

Anomalous temperature-induced volume contraction in GeTe

Enhancing the Thermoelectric Properties of Germanium Antimony Tellurides by Substitution with Selenium in Compounds GenSb2(Te1–xSex)n+3 (0 ≤ x ≤ 0.5; n ≥ 7)

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Thermoelectric efficiency of (1 − x)(GeTe) x(Bi₂Se_0.2Te_2.8) and implementation into highly performing thermoelectric power generators

Thermoelectric efficiency of (1 − x)(GeTe) x(Bi₂Se_0.2Te_2.8) and implementation into highly performing thermoelectric power generators

Enhancing the Thermoelectric Properties of Germanium Antimony Tellurides by Substitution with Selenium in Compounds Ge_nSb₂(Te_1–xSe_x)_n+3 (0 ≤ x ≤ 0.5; n ≥ 7)