Stable metal–insulator transition in epitaxial SmNiO3 thin films

• Published in: Journal of solid state chemistry 2012-06, Vol.190, p.233-237
• Main Authors: Ha, Sieu D., Otaki, Miho, Jaramillo, R., Podpirka, Adrian, Ramanathan, Shriram
• Format: Article
• Language: English
• Subjects: Annealing; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Correlation; Cross-disciplinary physics: materials science; rheology; Deposition by sputtering; Electron states; Electronics; Epitaxial growth; Exact sciences and technology; High pressure synthesis; Materials science; Metal-insulator transitions and other electronic transitions; Metal–insulator transition; Methods of crystal growth; physics of crystal growth; Methods of deposition of films and coatings; film growth and epitaxy; Optoelectronics; Oxides; Physics; Samarium; Samarium nickelate; SmNiO3; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Thin films
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2012.02.047

Samarium nickelate (SmNiO3) is a correlated oxide that exhibits a metal–insulator transition (MIT) above room temperature and is of interest for advanced electronics and optoelectronics. However, studies on SmNiO3 thin films have been limited to date, in part due to well-known difficulties in stabilizing the Ni3+ valence state during growth, which are manifested in non-reproducible electrical characteristics. In this work, we show that stable epitaxial SmNiO3 thin films can be grown by rf magnetron sputtering without extreme post-deposition annealing conditions using relatively high growth pressure (>200mTorr). At low growth pressure, SmNiO3 is insulating and undergoes an irreversible MIT at ∼430K. As pressure is increased, films become metallic across a large temperature range from 100 to 420K. At high pressure, films are insulating again but with a reversible and stable MIT at ∼400K. Phase transition properties can be continuously tuned by control of the sputtering pressure. X-ray diffraction (left) and resistivity-temperature characteristics (right) of sputtered SmNiO3 thin films as a function of sputtering pressure. As sputtering pressure increases, the out-of-plane lattice constant of SmNiO3 decreases, consistent with enhanced oxygen concentration. Concordantly, the electrical properties are strongly modified, and a reversible metal–insulator phase transition is observed at ∼400K in the film grown at high pressure. [Display omitted] ► Stable SmNiO3 films grown by rf sputtering without extreme annealing conditions. ► High sputtering pressures needed to fully stabilize SmNiO3. ► Reversible metal–insulator transition observed at ∼400K, similar to bulk. ► Electrical properties strongly modifiable by varying sputtering pressure.