Structural and electronic properties of Ti-and Ca-doped hexagonal TbInO3

Hexagonal TbInO3 exhibits spin liquid behavior at low temperatures and improper ferroelectricity at room temperature, and as such may host novel electronic and magnetic states upon carrier doping. This paper presents density functional theory (DFT) calculations of the electronic, dielectric, and defect properties of TbInO3. We study Ti4+ and Ca2+ as substitutional dopants replacing In3+ and Tb3+ to introduce electron-and hole-doping, respectively. Point defect calculations reveal that Ti4+ dopants introduce shallow defect states near the conduction band minimum, suggesting the possibility of n-Type conductivity, whereas Ca2+ dopants result in deep in-gap states. We also analyze changes to structural properties with relatively large (8%-16%) Ca and Ti concentrations. We utilize molecular beam epitaxy (MBE) to synthesize epitaxial thin films of TbInO3 doped with Ti4+ and Ca2+, and use scanning transmission electron microscopy (STEM) imaging to show that the experimental films corroborate the doping-induced structural changes found with DFT. However, all samples remain electrically insulating, which we attribute to the localization of added carriers on the Tb cation. Finally, we propose charge-Transfer doping as an alternative strategy to induce conductivity in TbInO3, and identify several possible substrates to achieve this.