Abstract
Polycrystalline Sr1−xTi0.9Nb0.1O3−δ (x = 0, 0.1, 0.2) ceramics have been prepared by the solid state method and their structural and thermoelectric properties have been studied by neutron powder diffraction (NPD), thermal, and transport measurements. The structural analysis of Sr1-xTi0.9Nb0.1O3−δ (x = 0.1, 0.2) confirms the presence of a significant amount of oxygen vacancies, associated with the Sr-deficiency of the materials. The analysis of the anisotropic displacement parameters (ADPs) indicates a strong softening of the overall phonon modes for these samples, which is confirmed by the extremely low thermal conductivity value (κ ≈ 1.6 W m-1 K−1 at 823 K) found for Sr1−xTi0.9Nb0.1O3−δ (x = 0.1, 0.2). This approach of introducing A-site cation vacancies for decreasing the thermal conductivity seems more effective than the classical substitution of strontium by rare-earth elements in SrTiO3 and opens a new optimization scheme for the thermoelectric properties of oxides.
Highlights
Thermoelectric (TE) materials enable direct conversion of waste heat into electrical energy, or vice versa; they can pump heat by using electricity through the thermoelectric effect
A high thermoelectric performance involves the unusual combination of high electrical conductivity together with a high Seebeck coefficient and low thermal conductivity
We find that a conspicuous effect on thermal properties is associated with the introduction of Sr2+ vacancies, leading to an extremely low thermal conductivity, achieving competitive values of κ for applications of ≈ 1.6 W m−1 K−1 at 823 K
Summary
Thermoelectric (TE) materials enable direct conversion of waste heat into electrical energy, or vice versa; they can pump heat by using electricity through the thermoelectric effect By exploiting these properties, thermoelectric device applications are concerned with power generation and environmental-friendly refrigeration [1,2,3,4,5]. Despite the significant benefits of thermoelectric devices, such as low cost electricity, green energy technology without using any moving part, stability, and reliability, the correct performance largely depends on the material efficiency [6]. This efficiency may be evaluated in terms of the figure of merit (zT) (Equation (1)): zT =. Since κ has electronic (κe ) and lattice (κL ) contributions, one approach to optimize zT is to target a reduction in κL , without impairing the electron-transport properties
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