Enhanced thermoelectric response of acid treated conducting polymer thin films.

We report the evolution of high temperature thermoelectric properties of SrTiO3 thin films doped with Nb and oxygen vacancies. Structure-property relations in this important thermoelectric oxide are elucidated and the variation of transport properties with dopant concentrations is discussed. Oxygen vacancies are incorporated during growth or annealing in Ar/H2 above 800 K. An increase in lattice constant due to the inclusion of Nb and oxygen vacancies is found to result in an increase in carrier density and electrical conductivity with simultaneous decrease in carrier effective mass and Seebeck coefficient. The lattice thermal conductivity at 300 K is found to be 2.22 W m(-1) K(-1), and the estimated figure of merit is 0.29 at 1000 K.

Thermoelectric (TE) metal oxides overcome crucial disadvantages of traditional heavy-metal-alloy-based TE materials, such as toxicity, scarcity, and instability at high temperatures. Here, we report the TE properties of metal oxide superlattices, composed from alternating layers of 5% Pr 3+ -doped SrTiO 3−δ (SPTO) and 20% Nb 5+ -doped SrTiO 3−δ (STNO) fabricated using pulsed laser deposition (PLD). Excellent stability is established for these superlattices by maintaining the crystal structure and reproducing the TE properties after long-time (20 h) annealing at high temperature (∼1000 K). The introduction of oxygen vacancies as well as extrinsic dopants (Pr 3+ and Nb 5+ ), with different masses and ionic radii, at different lattice sites in SPTO and STNO layers, respectively, results in a substantial reduction of thermal conductivity via scattering a wider range of phonon spectrum without limiting the electrical transport and thermopower, leading to an enhancement in the figure-of-merit (ZT). The superlattice composed of 20 SPTO/STNO pairs, 8 unit cells of each layer, exhibits a ZT value of 0.46 at 1000 K, which is the highest among SrTiO 3 -based thermoelectrics. ■ INTRODUCTIONThe rapid increase in global energy consumption and the inability of conventional energy conversion technologies, such as combustion of fossil fuels, to reduce their negative impact on environment, have led to significant activities in developing alternative energy conversion technologies. One of these promising technologies is thermoelectrics (TE), which possesses sustainable, reliable, and scalable characteristics in converting waste heat into electricity. Currently, TE devices cannot replace the traditional power generation systems, because of their relatively low conversion efficiencies. The performance of TE materials is evaluated in terms of a dimensionless figure-of-merit (ZT), which is defined aswhere σ is the electrical conductivity, S is the Seebeck coefficient, T is the absolute temperature, and λ is the total thermal conductivity. 1 The total thermal conductivity consists of contributions from electronic (λ e ) and lattice (λ l ) thermal conductivities (i.e., λ = λ e + λ l ). Unfortunately, all of the physical quantities used to describe ZT are strongly correlated, which makes the enhancement of ZT extremely challenging. 2 The TE community has been intensively trying to achieve ZT ≥ 3 in order to make the performance of TE solid-state devices competitive with traditional energy conversion systems. Although heavy-metal-based alloys, such as SnSe (∼2.6) 3 and PbTe (∼2.2), 4 exhibit high ZT values, they are not attractive for a wide range of applications, because they are toxic, decomposable, and their constituents are not naturally abundant. For these reasons, metal oxides, which do not have the above-mentioned disadvantages of traditional TE materials, emerge as reasonable and viable alternatives. Among metal oxides, SrTiO 3 (STO) is a promising TE material, particularly at high temperatures, because it has a high melting point ...

We study epitaxial SrTiO3 interfaced with Nb-doped SrTi1-xNbxO3 (x = 0, 0.125, 0.25, 0.375, and 0.5) by full-potential density functional theory. From the electronic band structures obtained by our ab-initio calculations we determine the dependence of the induced metallicity on the Nb concentration. We obtain a monotonous increase of the carrier density with the Nb concentration. The results are confirmed by experiments for SrTi0.88Nb0.12O3 and SrTi0.8Nb0.2O3, demonstrating the predictive power and limitations of our theoretical approach. We also show that the Seebeck coefficient decreases monotonously with increasing temperature.

We demonstrate that the thermoelectric properties of highly oriented Al-doped zinc oxide (AZO) thin films can be improved by controlling their crystal orientation. The crystal orientation of the AZO films was changed by changing the temperature of the laser deposition process on LaAlO3 (100) substrates. The change in surface termination of the LaAlO3 substrate with temperature induces a change in AZO film orientation. The anisotropic nature of electrical conductivity and Seebeck coefficient of the AZO films showed a favored thermoelectric performance in c-axis oriented films. These films gave the highest power factor of 0.26 W m−1 K−1 at 740 K.