Sintering temperature effect on thermoelectric properties and microstructure of the grained Bi1.9Gd0.1Te3 compound

Journal of the European Ceramic Society

2020

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Elemental composition, crystal and grain structures, specific electrical resistivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure-of-merit of n-type grained Bi 1.9 Gd 0.1 Te 3 compounds, spark-plasma-sintered at T S = 690, 720, 750, 780 and 810 K, have been studied. All the samples are highly textured along the 001 direction parallel to the pressing direction. The average grain size measured along the pressing direction is much less as compared to the average grain size measured in the perpendicular direction. A strong anisotropy in the transport properties measured along directions parallel and perpendicular to the pressing direction was found within the 290 ÷ 630 K interval. Electrical resistivity decreases and thermal conductivity increases for parallel orientation as compared to these properties for perpendicular orientation. The T S -effect on thermoelectric figure-of-merit of textured Bi 1.9 Gd 0.1 Te 3 compounds has been found and analyzed. Highest thermoelectric figure-of-merit (∼0.75) was observed for sample with T S = 750 K at perpendicular orientation.

Section: Methodsmentioning

confidence: 99%

Thermoelectric properties of the textured Bi1.9Gd0.1Te3 compounds spark-plasma-sintered at various temperatures

Journal of the European Ceramic Society

2020

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“…In the grained thermoelectrics based on bismuth telluride, Bi 2 Te 3 , the grain boundaries are usually acting as n-type dopants, enhancing electron concentration [24][25][26]. Moreover, some thermoelectrics having a layered crystal structure, like Bi 2 Te 3 and Bi 2 Te 3 -based alloys [27][28][29][30][31][32][33][34][35][36][37][38], SnSe [39][40][41], BiCuSeO [42], Ca 3 Co 4 O 9 [43,44], are readily textured via technological processes based on uniaxial pressuring a starting powder. For the textured samples, a preferential orientation of the grains takes place.…”

Section: Introductionmentioning

confidence: 99%

Comparative analysis of the thermoelectric properties of the non-textured and textured Bi1.9Gd0.1Te3 compounds

Journal of Solid State Chemistry

2020

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Features in thermoelectric properties of non-textured and textured Bi 1.9 Gd 0.1 Te 3 compounds are analysed. Cold isostatic pressuring was applied to prepare non-textured samples, whereas textured samples were fabricated via spark plasma sintering. The same starting powder was used for both preparation methods. Texturing [001] axis coincided with direction of spark plasma sintering pressuring. Thermoelectric properties of non-textured sample are isotropic, that is due to random grains orientation. Strong anisotropy in electrical resistivity and thermal conductivity, measured in directions parallel and perpendicular to direction of spark plasma sintering pressuring was found for textured sample. Texturing is partially recovering anisotropy inherent to single-crystalline bismuth telluride via redistributing anisotropic contributions from crystal a-b plane and c-axis into thermoelectric properties. Electrical resistivity decreases and thermal conductivity increases for parallel measuring orientation as compared to these properties for perpendicular measuring orientation. Highest thermoelectric figure-of-merit (~0.75 at~420 K) was observed for textured sample for perpendicular measuring orientation.

“…Synthesis conditions were reported in detail in Ref. [11,26]. Spark plasma sintering method by using a SPS-25/10 system was applied to compact the starting powder at pressure of 40 MPa and sintering time of 150 s resulting in the Ø20 mm × 15 mm cylinders.…”

Section: Methodsmentioning

confidence: 99%

Anisotropy of the grain size effect on the electrical resistivity of n-type Bi1.9Gd0.1Te3 thermoelectric textured by spark plasma sintering

Journal of the European Ceramic Society

2020

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Spark plasma sintering (SPS) was applied to prepare textured Bi 1.9 Gd 0.1 Te 3 compounds with various grain structures, tuned by changing in the sintering temperature. The grains forming ordered lamellar structure under texturing are elongated in plane oriented perpendicularly to SPS-pressing direction. As result, average grain size measured parallel to this direction and corresponding to fine-grained samples happened to be much less as compared to relevant size for perpendicular direction characteristic for coarse-grained samples. Anisotropy in electrical resistivity inherent for single crystal was found to be partially recovered in textured samples, i.e. resistivity measured along directions parallel or perpendicular to SPS-pressuring direction is different. Moreover, resistivity for both directions is increasing with decreasing in grain size or with decreasing in intergrain distance. Grain size effect on resistivity due to grain boundary scattering of electrons was found to be anisotropic, since the effect is observed for different ranges of change in average grain sizes.