Freestanding perovskite and infinite-layer nickelate membranes

Abstract

Following the discovery of superconductivity in hole-doped NdNiO2 infinite-layer thin films, extensive research has been conducted particularly to compare these materials with cuprates. Superconductivity has also been observed in nickelate thin films with other rare-earth elements such as Pr and La, but not in their bulk forms, suggesting a critical role for substrate-induced strain/interface or dimensionality effects. In this study, we used water-soluble (Ca,Sr)3Al2O6 sacrificial layers to fabricate freestanding perovskite nickelate membranes and explore the phase transformation to infinite layers of the membranes via topotactic reduction in the absence of any template effect from the substrate. Highly metallic NdNiO3 membranes with bulk-like hysteretic metal-to-insulator transitions could be obtained when transferred from a LaAlO3 substrate. The topotactic reduction of these membranes with CaH2 was shown to be successful as characterized by the expected decrease of the out-of-plane cell parameter and absence of apical oxygens. The reduced membranes, however, displayed insulating characteristics similar to those of bulk infinite-layer nickelates. Our findings strongly indicate that a template is necessary to stabilize a coherent and robust infinite-layer phase with optimal transport properties.

Source-reported materials — not catalogue approval

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