Synthesis and characterization of bulk Nd Sr NiO and Nd Sr NiO.

The recent reports of superconductivity in Nd Sr NiO/SrTiO heterostructures have reinvigorated interest in potential superconductivity of low-oxidation state nickelates. Synthesis of Ni-containing compounds is notoriously difficult. In the current work, a combined sol-gel combustion and high-pressure annealing technique was employed to prepare polycrystalline perovskite Nd Sr NiO ( = 0, 0.1, and 0.2). Metal nitrates and metal acetates were used as starting materials, and the latter were found to be superior to the former in terms of safety and reactivity. The Nd Sr NiO compounds were subsequently reduced to Nd Sr NiO using calcium hydride in a sealed, evacuated quartz tube. To understand the synthesis pathway, the evolution from NdNiO to NdNiO was monitored using synchrotron x-ray diffraction during the reduction process. Electrical transport properties were consistent with an insulator-metal transition occurring between = 0 and 0.1 for Nd Sr NiO. Superconductivity was not observed in our bulk samples of Nd Sr NiO. Neutron diffraction experiments at 3 and 300 K were performed on NdSrNiO, in which no magnetic Bragg reflections were observed, and the results of structural Rietveld refinement are provided.