Self-Nanostructuring in SrTiO3: A Novel Strategy for Enhancement of Thermoelectric Response in Oxides


Azough F., Gholinia A., Alvarez-Ruiz D. T., Duran E. Ç., Kepaptsoglou D. M., Eggeman A. S., ...More

ACS Applied Materials and Interfaces, vol.11, no.36, pp.32833-32843, 2019 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 11 Issue: 36
  • Publication Date: 2019
  • Doi Number: 10.1021/acsami.9b06483
  • Journal Name: ACS Applied Materials and Interfaces
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.32833-32843
  • Keywords: 3D electron diffraction, aberration corrected microscopy, nanostructuring, oxide thermoelectric, perovskite, strontium titanate, thermal conductivity
  • Istanbul Technical University Affiliated: No

Abstract

Nanostructuring is recognized as an efficient route for enhancing thermoelectric response. Here, we report a new synthesis strategy for nanostructuring oxide ceramics and demonstrate its effectiveness on an important n-type thermoelectric SrTiO3. Ceramics of Sr0.9La0.1TiO3 with additions of B2O3 were synthesized by the mixed oxide route. Samples were sintered in air followed by annealing in a reducing atmosphere. Crystallographic data from X-ray and electron diffraction showed Pm3 m cubic symmetry for all the samples. High-resolution transmission electron microscopy (HRTEM) showed the formation of a core-shell type structure within the grains for the annealed ceramics. The cores contain nanosize features comprising pairs of nanosize voids and particles; the feature sizes depend on annealing time. Atomic-resolution, high-angle annular-dark-field imaging and electron energy loss spectroscopy in the scanning transmission electron microscopy (STEM-HAADF-EELS) showed the particles to be rich in Ti and the areas around the voids to contain high concentrations of Ti3+. Additionally, dislocations were observed, with significantly higher densities in the shell areas. The observed dislocations are combined (100) and (110) edge dislocations. The major impact of the core-shell type microstructures, with nanosize inclusions, is the reduction of the thermal conductivity. Sr0.9La0.1TiO3 ceramics containing grain boundary shells of size ≈ 1 μm and inclusions in the core of 60-80 nm exhibit a peak power factor of 1600 μW/m·K2 at 540 K; at 1000 K, they exhibit a low thermal conductivity (2.75 W/m·K) and a power factor of 1050 μW/m·K2 leading to a high of ZT of 0.39 ± 0.03. This is the highest ZT reported so far for Sr0.9La0.1TiO3 based-compositions. This nanostructuring strategy should be readily applicable to other functional oxides.