Understanding the electronic structure and transport properties of A-site SrTiO3-δ ceramics with enhanced configuration entropy

• Published in: Ceramics international Vol. 50; no. 21; pp. 40736 - 40746
• Main Authors: Kanas, Nikola, Madathil, Reshma K., Sharma, Annu, Miljević, Bojan, Rakić, Srđan, Bhattacharya, Subramshu S., Srdić, Vladimir V., Armaković, Stevan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-11-2024
• Subjects: Conductivity; Density functional theory (DFT); Oxygen vacancies; Perovskites; Conductivity; Oxygen vacancies; Perovskites; Density functional theory (DFT)
• ISSN: 0272-8842
• DOI: 10.1016/j.ceramint.2024.07.137

Since SrTiO3 is attractive due to its versatile electronic properties ranging from dielectric to semiconducting behavior, the effect of systematic co-substitution of various A-site cations on the electronic structure and transport properties of oxygen-deficient SrTiO3-δ bulk ceramics was analyzed. The materials were synthesized by reverse co-precipitation method and densified by spark plasma sintering (SPS) in a vacuum, followed by a post-thermal treatment in a reducing atmosphere (5 % H2/Ar). The phase purity was confirmed by X-ray diffraction (XRD), different microstructures were revealed by scanning electron microscopy (SEM), and characterization in terms of electrical conductivity (σel) and Seebeck coefficient (S) were performed. The largest power factor was obtained with Sr0.25Ca0.25Na0.25La0.25TiO3-δ by maintaining electrical conductivity while increasing the Seebeck coefficient. Density Functional Theory (DFT) calculations were applied to obtain information on band structures, the projected density of states (PDOS), and electron density differences (EDD). Band structures indicated that oxygen deficiency essentially changed the conductive nature of the studied materials by shifting the Fermi level to the conductive zone, while PDOS plots define the role of each element located at the A site. The electronic structure is affected to the greatest extent in the cases when Nd and Pr are present at the A-site. However, the obtained experimental and computational (DFT) results could not completely match and explain all phenomena since understanding the effect of different cations at A-site on oxygen vacancy formation seems to be a challenging task, and therefore, some hypotheses are proposed. This work attempts to understand the role of a particular cation at A-site on the electronic band structure and its relevance to the formation of oxygen vacancies, thereby providing valuable insights for future high-entropy perovskite titanates with improved transport properties.