Preparation of γ-LaSy (1.33<y<1.50) alloys by the pressure-assisted reaction sintering method and their thermoelectric properties

Abstract

The pressure-assisted reaction sintering (PARS) method was used to prepare thermoelectric elements of the γ-phase lanthanum sesquisulfide solid solution alloys which exist over a wide homogeneity range: LaSy (1.33<y<1.5). A mixture of powders of stoichiometric lanthanum sesquisulfide (La2S3) and lanthanum trihydride (LaH3) was reaction sintered in a hot-press to make the desired composition of γ-LaSy. This method produced black dense single-phase γ-LaSy pellets with a theoretical density of 97% or better. The thermoelectric properties (electrical resistivity and Seebeck coefficient) of the samples prepared by the PARS technique were measured. The room temperature electrical resistivity and Seebeck coefficient of γ-LaSy varied in a systematic manner with the electron concentration indicating that γ-LaSy alloys behave like a simple metal. Although the current carriers appear to be quite heavy (drift mobility ∼3 cm2/V s), the temperature dependence (up to 1000 °C) of these properties of LaS1.42 were found to be linear functions, which is in accord with the above observations. The thermoelectric figure of merit based on the measured resistivity and Seebeck coefficient and an estimated thermal conductivity for LaS1.42 is 0.75×10−3 °C−1 at 1000 °C, which is comparable to those of the state-of-the-art materials such as silicon–germanium alloys at 1000 °C.

Thermoelectric Properties of NdGd1+x S3 Prepared by CS2 Sulfurization

“…The cubic lattice parameter is essentially unchanged in the compositional range from NdGdS 3 to NdGd 1.08 S 3 , which is similar to the trend seen in La 2+2x S 3 . 9 The cubic lattice parameter of NdGd 1+x S 3 , which is between 0.845 nm and 0.846 nm, is almost the mean of those of c-Nd 2 S 3 (0.853 nm) and c-Gd 2 S 3 (0.838 nm).…”

Synthesis of La<SUB>2</SUB>S<SUB>3</SUB> Thin Films by Sulfurization of LaCl<SUB>3</SUB> and CS(NH<SUB>2</SUB>)<SUB>2</SUB>

“…Although the concentration of metal vacancies increases with the sulfur content, the lattice parameter ofLa 2 S 3 essentially remains unchanged over the solid solution region. 1) High thermoelectric performances were observed in -La 2 S 3 phase with high sulfur content. 1,2,9) The lanthanumrich sample promotes the formation of -La 2 S 3 , whose composition is nearly identical to that of La 3 S 4 .…”

“…[1][2][3][4][5][6][7][8][9][10][11] However, in order to apply these materials to thermoelectric devices for smallscale refrigeration and power generation, it is required to prepare thin films. A majority of the previous studies have been confined to the investigation of bulk materials.…”

Preparation of Ln3−xEu x S4 (Ln=Ce, Pr, and Nd) ceramics by pressureless sintering

“…The performance of the thermoelectric materials is characterized by the figure of merit ZT given by ZT=S 2 T/ρκ, where S, T, ρ, and κ are the Seebeck coefficient, the absolute temperature, the electrical resistivity, and the thermal conductivity, respectively. High performance thermoelectric materials must have high figure of merit ZT.The gamma phase rare earth sesquisulfides with Th 3 P 4 defect structure have been intensively studied for their thermoelectric properties [1][2][3][4][5][6][7][8] . The chemical formula of γ-phase rare earth sesquisulfides can be expressed as Ln 3-x □ x S 4 , where Ln is rare earth metal, □ is a rare earth metal vacancy, and 0≤x≤1/3.…”

“…The gamma phase rare earth sesquisulfides with Th 3 P 4 defect structure have been intensively studied for their thermoelectric properties [1][2][3][4][5][6][7][8] . The chemical formula of γ-phase rare earth sesquisulfides can be expressed as Ln 3-x □ x S 4 , where Ln is rare earth metal, □ is a rare earth metal vacancy, and 0≤x≤1/3.…”