High Power Factor Nb-Doped TiO₂ Thermoelectric Thick Films: Toward Atomic Scale Defect Engineering of Crystallographic Shear Structures

Abstract

Donor-doped TiO2-based materials are promising thermoelectrics (TEs) due to their low cost and high stability at elevated temperatures. Herein, high-performance Nb-doped TiO2 thick films are fabricated by facile and scalable screen-printing techniques. Enhanced TE performance has been achieved by forming high-density crystallographic shear (CS) structures. All films exhibit the same matrix rutile structure but contain different nano-sized defect structures. Typically, in films with low Nb content, high concentrations of oxygen-deficient {121} CS planes are formed, while in films with high Nb content, a high density of twin boundaries are found. Through the use of strongly reducing atmospheres, a novel Al-segregated {210} CS structure is formed in films with higher Nb content. By advanced aberration-corrected scanning transmission electron microscopy techniques, we reveal the nature of the {210} CS structure at the nano-scale. These CS structures contain abundant oxygen vacancies and are believed to enable energy-filtering effects, leading to simultaneous enhancement of both the electrical conductivity and Seebeck coefficients. The optimized films exhibit a maximum power factor of 4.3 × 10–4 W m–1 K–2 at 673 K, the highest value for TiO2-based TE films at elevated temperatures. Our modulation strategy based on microstructure modification provides a novel route for atomic-level defect engineering which should guide the development of other TE materials.

Electrical Property Enhancement in Orientation‐Modulated Perovskite La‐Doped SrTiO3 Thermoelectric Thin Films

“…Due to the high-temperature endurance, chemical stability, non-toxicity, and abundance in earth, oxides are irreplaceable as thermoelectrics. [13][14][15][16][17] In n-type thermoelectrics, there were researches on ZnO, [18][19][20][21][22][23] CdO, [24] TiO 2 , [25,26] In 2 O 3 [27][28][29] -based simple oxides, and Bi 2 O 2 Se, [30,31] Bi 2 LnO 4 Cu 2 Se 2 , [32] Sr 2 MO 2 Cu 2 Se 2 (M = Co, Ni, Zn) [33] -based layered oxides, while the simple crystal structure providing few elemental sites to be tuned, and low symmetry of layered oxides resulting in low electron effective mass, [34][35][36][37][38] limited the enhancement of their electrical properties. Strontium Titanate (SrTiO 3 ) as a cubic phase perovskite oxide possesses high symmetry and high density of states near the conduction band minimum (CBM), thus having a relatively large density of states effective mass and outperforming power factors.…”