Thermoelectric Efficiency of Reduced SrTiO₃ Ceramics Modified with La and Nb

Abstract

Ceramics of LaxSr1−xNbyTi1−yO3 (LSNT) were synthesized under various reducing atmospheres. Covering the specimens with graphite carbon felt under an Ar‐gas flow during sintering drastically enhanced the electrical conductivity, σ. Ti K‐edge absorption spectra indicated the presence of Ti3+ for heavily reduced specimens. The increase in conductivity was attributed to the 3d band of Ti3+. The maximum value for the figure of merit, ZT, was obtained for strontium titanate ceramics modified with both 5 mol% La and 5 mol% Nb, namely 5/5‐LSNT, exhibiting a ZT value of ~0.221 at 473 K. This high ZT value was almost 1.5 × larger than that of the conventional 10 mol% La‐doped sample, 10/0‐LSNT (ZT~0.144), and was mainly attributed to the larger Seebeck coefficient of the material.

Design of SrTiO3-Based Thermoelectrics by Tungsten Substitution

“…9B,C and confirms the minor effect from the charge carriers on the heat transfer. Although in the case of the substitution of titanium with heavy tungsten one may anticipate significant decrease in κ ph due to mass-difference impurity scattering [33][34][35], the calculated values of the thermal conductivity are only moderately below or similar to those observed for other low-substituted perovskite-type titanates, cited above for PF comparison [16,17,24,62]. Separation of the phase impurities at nanoscale level in SrTi 0.94 W 0.06 O 3±δ , which are likely to act as phonon scattering interfaces, also did not result in any evident lowering of κ ph , though corresponding impact can be hindered by other structural and microstructural effects.…”

“…Donor substitution is usually accomplished using rare-earth elements for A-site substitution or transition-metal cations, having a stable oxidation state of higher than four for the B-site substitution (e.g., niobium). Co-substitution in both A-and B-sites of SrTiO 3 has also been proposed for quasi-independent tuning of the power factor (PF, σ×α 2 ) and thermal conductivity (κ) [12][13][14]. Ceramics processing in reducing conditions at elevated temperatures is essential for creating an appropriate concentration of the electronic defects in titanates and to achieve reasonable power factor.…”

Doping site dependent thermoelectric properties of epitaxial strontium titanate thin films

“…26 The scattering centers are the randomly distributed oxygen vacancies 13 (usually doubly ionized) 5 and the ionized dopants that substitute at the A-sites. 14 For doped STO lms with lower ionized impurity and hence carrier densities, polar optical phonon scattering has also been reported as an important mechanism that limits carrier mobility around 300 K. 4,27 However, in our lms, which have high ionized dopant and carrier densities, the scattering at 300 K is most likely due to ionized impurities, with possible contribution also from polarons. It is interesting to note that in many wide band-gap degenerate oxides, scattering by ionized impurities has been reported as the dominant scattering mechanism at room temperature.…”

“…12 Another approach is to create point defects such as oxygen vacancies 13 and extrinsic doping of elements that enhance mass-uctuation scattering. [14][15][16][17] Extrinsic dopants, of different masses and ionic radii compared to Sr and Ti, that occupy A and B sites can be effectively used for scattering phonons. In single doped STO, either Sr (A-site) or Ti (B-site) gets substituted with elements such as La, Y, Pr, etc.…”

Annealing of Strontium Titanate Based Thermoelectric Materials by Graphite: Mechanistic Analysis by Spectroscopic and Chromatographic Techniques

“…High ZT values of 0.4 were achieved at 769–1009 K. Teranishi et al . synthesized La/Nb co‐doped SrTiO 3 via solid‐state reaction . They were annealed within a graphite felt at 1550 °C for 4 h in Argon atmosphere.…”