  The recent reports of superconductivity in Nd1-xSrxNiO2/SrTiO3
heterostructures have reinvigorated interest in potential superconductivity of
low-valence nickelates. Synthesis of Ni1+-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
Nd1-xSrxNiO3 (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 Nd1-xSrxNiO3 compounds were subsequently
reduced to Nd1 xSrxNiO2 using calcium hydride in a sealed, evacuated quartz
tube. To understand the synthesis pathway, the evolution from NdNiO3 to NdNiO2
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 Nd1-xSrxNiO3.
Superconductivity was not observed in our bulk samples of Nd1-xSrxNiO2. Neutron
diffraction experiments at 3 K and 300 K were performed on Nd0.9Sr0.1NiO2, in
which no magnetic Bragg reflections were observed, and the results of
structural Rietveld refinement are provided.
