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

Abstract

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.

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

“…Before analyzing the grain size effect on the electrical resistivity of the textured Bi 1.9 Gd 0.1 Te 3 compounds, it would be helpful to briefly consider main features of these compounds reported earlier in Ref. [11]. XRD pattern for the starting Bi 1.9 Gd 0.1 Te 3 powder is shown in Fig.…”

“…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.…”

“…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. Different SPS-temperatures, T S , equal to 690, 720, 735, 750, 780, and 810 K were used to prepare the samples with various grain structures [11].…”

“…Besides this difference in number of the grain boundaries, ability of these boundaries to scatter the electrons can be also different for both directions mentioned additionally effecting on the grain size effect on ρ. It is known that the grained Bi 2 Te 3 compound can be readily texturing during preparation processes based on uniaxial loading applied to an initial powder under compacting and sintering [5][6][7][8][9][10][11][12][13][14]. Therefore, this compound can be reasonably chosen to examine anisotropy of the grain size effect on the electrical resistivity in the textured materials.…”

“…A few technological ways can be applied to texture the Bi 2 Te 3 and Bi 2 Te 3 -based alloys including extrusion, hot pressing, spark plasma sintering. Particularly, spark plasma sintering was successfully applied to prepare the n-type textured Bi 1.9 Gd 0.1 Te 3 compounds with various grain structures differing in shape and size of the grains [11]. Therefore, these compounds are suitable to find and analyze anisotropy of the grain size effect on the electrical resistivity in grained thermoelectrics.…”