Abstract
The recent discovery of nickelate superconductivity represents an important step toward understanding the four-decade mastery of unconventional high-temperature superconductivity. However, the synthesis of the infinite-layer nickelate superconductors shows great challenges. Particularly, surface capping layers are usually unitized to facilitate the sample synthesis. This leads to an important question whether nickelate superconductors with d(9) configuration and ultralow valence of Ni(1+) are in metastable state and whether nickelate superconductivity can be robust? In this work, a series of redox cycling experiments are performed across the phase transition between perovskite Nd(0.8)Sr(0.2)NiO(3) and infinite-layer Nd(0.8)Sr(0.2)NiO(2). The infinite-layer Nd(0.8)Sr(0.2)NiO(2) is quite robust in the redox environment and can survive the cycling experiments with unchanged crystallographic quality. However, as the cycling number goes on, the perovskite Nd(0.8)Sr(0.2)NiO(3) shows structural degradation, suggesting stability of nickelate superconductivity is not restricted by the ultralow valence of Ni(1+), but by the quality of its perovskite precursor. The observed robustness of infinite-layer Nd(0.8)Sr(0.2)NiO(2) up to ten redox cycles further indicates that if an ideal high-quality perovskite precursor can be obtained, infinite-layer nickelate superconductivity can be very stable and sustainable under environmental conditions. This work provides important implications for potential device applications for nickelate superconductors.