Synthesis and characterization of bulk Nd

The recent reports of superconductivity in Nd(1–x)Sr(x)NiO(2)/SrTiO(3) heterostructures have reinvigorated interest in potential superconductivity of low-oxidation state nickelates. Synthesis of Ni(1+)-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(1–x)Sr(x)NiO(3) (x = 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(1–x)Sr(x)NiO(3) compounds were subsequently reduced to Nd(1–x)Sr(x)NiO(2) using calcium hydride in a sealed, evacuated quartz tube. To understand the synthesis pathway, the evolution from NdNiO(3) to NdNiO(2) was monitored using in situ synchrotron x-ray diffraction during the reduction process. Electrical transport properties were consistent with an insulator-metal transition occurring between x = 0 and 0.1 for Nd(1–x)Sr(x)NiO(3). Superconductivity was not observed in our bulk samples of Nd(1–x)Sr(x)NiO(2). Neutron diffraction experiments at 3 and 300 K were performed on Nd(0.9)Sr(0.1)NiO(2), in which no magnetic Bragg reflections were observed, and the results of structural Rietveld refinement are provided.