High-Temperature Thermoelectric Properties of (1 − x) SrTiO3 − (x) La1/3NbO3 Ceramic Solid Solution

Abstract

Ceramics based on SrTiO 3 are of growing interest as thermoelectric materials because of their high-temperature stability and non-toxicity. Substitution of La and Nb into the perovskite structure provides opportunities to control both the microstructure and properties. Ceramic solid solutions of (1 À x) SrTiO 3 À (x) La 1/3 NbO 3 were prepared by the mixed oxide route, using compositional steps of x = 0.1. Pressed pellets were sintered at temperatures of 1573 K to 1723 K in air. Addition of aliovalent ions (La 3+ , Nb 5+ ) on the A/B sites (Sr 2+ , Ti 4+ ) led to A-Site cation deficiency in the stoichiometric compositions and other defect structures which increased carrier concentration. A maximum ZT of 0.004 was obtained for the x = 0.2 stoichiometric sample, although much higher ZT values are possible by sample reduction.

Anisotropy and enhancement of thermoelectric performance of Sr0.8La0.067Ti0.8Nb0.2O3−δceramics by graphene additions

“…4c), shows a marked improvement upon addition of graphene/GO; this is directly linked to the increase in electrical conductivity. While the L2-SPS sample had a maximum ZT of 0.0002 at 950 K (similar to that for L2 samples sintered in air 16 ), the composite samples demonstrated an increase of at least two orders of magnitude. The composite L210G-SPS exhibited the highest ZT of 0.065 at 950 K. This is only marginally lower than the value reported by Feng et al 47 for pure SrTiO 3 -RGO composites (0.09 at 750 K).…”

“…56 The lattice parameters of the L2-SPS and the graphenebearing samples (3.912 AE 0.001Å) are comparable to those of the L2 samples sintered in air (3.913Å). 16 This suggests that the unit cell is not enlarged signicantly by oxygen vacancies in the heavily reduced L2 samples sintered in Ar/5% H 2 (ref. 15) in previous work.…”

“…4,6 We have previously shown that controlled doping on Sr/Ti sites of SrTiO 3 (STO), in addition to controlled vacancy formation within the system, can introduce signicant numbers of charge carriers. 15,16 Cationic vacancies in donor doped STO have been shown to increase carrier concentration and generate oxygen vacancies under reducing environment. These point defects play a crucial role in reducing thermal conductivity by scattering of phonons.…”

Prospects for Engineering Thermoelectric Properties in La1/3NbO3 Ceramics Revealed via Atomic-Level Characterization and Modeling

“…This can for instance can achieved by reducing the valence of the B-site element, either employing a thermal treatment in a reducing atmosphere (for instance during the sintering stage or as a separate post-treatment), an approach similar to that used for other TE oxides. 15,64 Perhaps the most promising approach is the partial substitution of both A and B sites with elements of different valance state, for instance Ca and Sr for the A-site and Ti and Mo for the B-site, respectively, before applying thermal treatment 15 Calculations also suggest that a functional grading of the material's electronic doping profile would widen its working temperature. It would also allow for band engineering, aimed to tune the density of states by exploiting the temperature dependence of the effective band degeneracy through a band convergence behaviour predicted to occur by our calculations.…”

“…7,[10][11][12] Of particular interest, La 1/3 NbO 3 (hereafter denoted LNO) is a leading contender as its vacancy content in the lattice, the highest among the A-site deficient perovskite family (whereby 2/3 of the A-sites are vacant), may promote glass-like low thermal conductivity 13 . The constituent cations of LNO, namely La and Nb, have been previously used as A-and B-site dopants respectively in SrTiO 3 (separately or as co-dopants), [14][15][16][17][18][19] in order to achieve improved thermoelectric properties. This shared chemistry thus provides a direct pathway to integration with STO in a binary system.…”