Spontaneous phase segregation of Sr2NiO3 and SrNi2O3 during SrNiO3 heteroepitaxy

摘要

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