Spontaneous phase segregation of Sr<sub>2</sub>NiO<sub>3</sub> and SrNi<sub>2</sub>O<sub>3</sub> during SrNiO<sub>3</sub> heteroepitaxy.
basic_science · Level V
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- Record sourced from PubMed, PMID 33674310.
- Also identified by DOI 10.1126/sciadv.abe2866 and PMC identifier 7935367.
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Abstract
Recent discovery of superconductivity in Nd<sub>0.8</sub>Sr<sub>0.2</sub>NiO<sub>2</sub> motivates the synthesis of other nickelates for providing insights into the origin of high-temperature superconductivity. However, the synthesis of stoichiometric <i>R</i> <sub>1-<i>x</i></sub> Sr <i><sub>x</sub></i> NiO<sub>3</sub> thin films over a range of <i>x</i> has proven challenging. Moreover, little is known about the structures and properties of the end member SrNiO<sub>3</sub> Here, we show that spontaneous phase segregation occurs while depositing SrNiO<sub>3</sub> thin films on perovskite oxide substrates by molecular beam epitaxy. Two coexisting oxygen-deficient Ruddlesden-Popper phases, Sr<sub>2</sub>NiO<sub>3</sub> and SrNi<sub>2</sub>O<sub>3</sub>, are formed to balance the stoichiometry and stabilize the energetically preferred Ni<sup>2+</sup> cation. Our study sheds light on an unusual oxide thin-film nucleation process driven by the instability in perovskite structured SrNiO<sub>3</sub> and the tendency of transition metal cations to form their most stable valence (i.e., Ni<sup>2+</sup> in this case). The resulting metastable reduced Ruddlesden-Popper structures offer a testbed for further studying emerging phenomena in nickel-based oxides.