Defect compensation by Cr vacancies and oxygen interstitials in $\mathrm{T}{\mathrm{i}}^{4+}$ -doped $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$ epitaxial thin films

Journal Article · Sat Oct 01 00:00:00 EDT 2016 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.94.155409· OSTI ID:1340807

Kaspar, Tiffany C.; Sushko, Peter V.; Bowden, Mark E.; Heald, Steve M.; Papadogianni, Alexandra; Tschammer, Carsten; Bierwagen, Oliver; Chambers, Scott A.

Epitaxial thin films of Cr2-xTixO3 were deposited by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) for 0.04 ≤ x ≤ 0.26. Ti speciation is verified by both x-ray photoelectron spectroscopy (XPS) and Ti K-edge x-ray absorption near-edge spectroscopy (XANES) to be Ti4+. Substitution of Ti for Cr in the corundum lattice is confirmed by modeling of the Ti K-edge extended x-ray absorption fine structure (EXAFS). Room temperature electrical transport measurements confirm the highly insulating nature of Ti-doped Cr2O3, despite the presence of aliovalent Ti4+. The resistivity of highly pure, undoped Cr2O3 was measured to be three orders of magnitude higher than for Ti-doped Cr2O3. Although the formation of Cr vacancies in Ti-doped Cr2O3 is found by density functional theory (DFT) calculations to be the energetically preferable defect compensation mechanism to maintain charge neutrality, an analysis of the XPS and EXAFS data reveal the presence of both Cr vacancies and oxygen interstitials at intermediate and high Ti concentrations, with a weak trend towards Cr vacancies as the Ti concentration increases. At low Ti concentrations, a strong dependence of the XPS Ti 2p core level peak width on concentration is observed. This dependence is attributed to the presence of widely spaced Ti dopants, which renders compensation of two or three Ti by a single oxygen interstitial or Cr vacancy, respectively, less probable. Instead, defect clusters of unknown type occur, although they may involve Cr vacancies. The defect compensation model developed here provides insight into previous, conflicting reports of n-type versus p-type conductivity in Ti-doped Cr2O3 at high temperature, and will inform future studies to exploit the wide variety of electronic and magnetic properties of corundum-structure oxides.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1340807
• Report Number(s): PNNL-SA-118171; 48341; KC0203020
• Journal Information: Physical Review B, Vol. 94, Issue 15; ISSN 2469-9950
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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