Optimizing Synthesis of Superconducting Infinite-Layer Nickelates*

Superconductivity was recently discovered in the infinite-layer nickelate Nd_0.8Sr_0.2NiO₂.¹ To proceed with further systematic studies in the superconducting properties of this material, it is important to establish a reproducible method to synthesize single-phase, single-crystalline Nd_0.8Sr_0.2NiO₂. The synthetic route to this infinite-layer nickelate structure poses two major challenges. First, the precursor perovskite phase is difficult to stabilize due to the unusually high formal nickel valence of Ni^+3.2 and the structural instability induced by chemical doping. Second, topochemical reduction on perovskite nickelates have shown limitations in coherent transition to the infinite-layer phase.² After careful optimization, we have successfully established a reproducible method to stabilize Nd_0.8Sr_0.2NiO₂ (001) epitaxial thin films on SrTiO₃ (001) substrate by pulsed-laser deposition and CaH₂-assisted topochemical reduction. The details of the optimization process and the dependence of structural and superconducting properties on growth conditions will be discussed.

1 Li, D. et al., Nature 572, 624 (2019).
2 Kawai, M. et al., Cryst. Growth Des. 10, 2044 (2010).