High-pressure Seebeck coefficients and thermoelectric behaviors of Bi and PbTe measured using a Paris-Edinburgh cell

Abstract

A new sample cell assembly design for the Paris-Edinburgh type large-volume press for simultaneous measurements of X-ray diffraction, electrical resistance, Seebeck coefficient and relative changes in the thermal conductance at high pressures has been developed. The feasibility of performing in situ measurements of the Seebeck coefficient and thermal measurements is demonstrated by observing well known solid-solid phase transitions of bismuth (Bi) up to 3 GPa and 450 K. A reversible polarity flip has been observed in the Seebeck coefficient across the Bi-I to Bi-II phase boundary. Also, successful Seebeck coefficient measurements have been performed for the classical high-temperature thermoelectric material PbTe under high pressure and temperature conditions. In addition, the relative change in the thermal conductivity was measured and a relative change in ZT, the dimensionless figure of merit, is described. This new capability enables pressure-induced structural changes to be directly correlated to electrical and thermal properties.

Strategies and challenges of high-pressure methods applied to thermoelectric materials

“…To date, several different types of cells or setups combining electrical and thermoelectric measurements have been devised, [45][46][47][48][49][50][51][52][53] and techniques that enable measurements of all relevant thermoelectric properties under the same conditions have been recently developed. 4,5,[54][55][56] All of these methods have their merits and limitations, but in any case there is still a need for more refined and accurate techniques. Among other things, methods for applying uniaxial stress or tension to thermoelectric materials are of great interest too.…”

“…We have monitored recent publications on this topic and plot in Fig. 4 61 PbTe and PbSe, 5,41,55 SnTe, 56 Ge and Ge-Si alloys, 43,62 Cs 8 Sn 44 , 63 Mg 2 Si:Al, 44 PdS, 6 CoSb 3 , 10 CuInTe 2 , 64 and Sr 8 Ga 16 Ge 30 . 65 It can be seen that these materials exhibit a diverse range of pressure-induced variations in their Seebeck coefficients at moderate pressures of several gigapascals.…”

“…(a) These dependences were measured on single-crystalline samples with carrier concentrations of p = 5 × 10 17 cm −3 in p-Bi 2 Te 3 (1), p = 3 × 10 18 cm −3 in p-Bi 2 Te 3 (2), p = 10 19 cm −3 in p-Bi 2 Te 3 (3), n = 10 18 cm −3 in n-Bi 2 Te 3 (1), n = 4 × 10 18 cm −3 in n-Bi 2 Te 3 (2), and n = 10 19 cm −3 in n-Bi 2 Te 3 (3). Data taken from Ovsyannikov et al, 52 Korobeinikov et al, 53 and Brazhkin et al 51 (b) Data taken from Polvani et al 58 and Meng et al [59][60][61] (c) Data taken from Ovsyannikov et al, 52 Brazhkin et al, 51 and Jacobsen et al 54 (d) Data taken from Ovsyannikov et al, 41 Jacobsen et al, 55 and Baker et al 5 (e) Data taken from Ovsyannikov et al, 62 Korobeinikov et al, 43 and Chen et al 63 (f ) Data taken from Meng et al, 65 Wu et al, 10 Morozova et al, 44 Baker et al, 56 Chen et al, 6 and Yu et al 64…”

“…4(d)] also suggested an increase in the ZT value with pressure up to 4 GPa. 5 Lead selenide has also been reported to transform to a gapless state at 2-3 GPa. 122 However, investigations of undoped p-type single crystals did not find any noticeable improvement in the power factor at these pressures.…”

“…[1][2][3][4] At present, thermoelectric materials are widely used in cooling technologies, in energy-efficient motors in the automotive industry, in biomedicine (for example in biothermal batteries for powering pacemakers), in photovoltaics, and in various military, aerospace, and other applications. [5][6][7][8][9] To be competitive compared with other energy sources, thermoelectric devices should be characterized by high values of certain performance parameters, the most important of which is the dimensionless figure of merit ZT, defined as…”