Is La 3 Ni 2 O 6.5 a Bulk Superconducting Nickelate?

Superconducting states onsetting at moderately high temperatures have been observed in epitaxially stabilized RE NiO 2 -based thin films. However, recently, it has also been reported that superconductivity at high temperatures is observed in bulk La 3 Ni 2 O 7-δ at high pressure, opening further possibilities for study. Here we report the reduction profile of La 3 Ni 2 O 7 in a stream of 5% H 2 /Ar gas and the isolation of the metastable intermediate phase La 3 Ni 2 O 6.45 , which is based on Ni 2+ . Although this reduced phase does not superconduct at ambient or high pressures, it offers insights into the Ni-327 system and encourages future study of nickelates as a function of oxygen content.