  Infinite layer nickelates provide a new route beyond copper oxides to address
outstanding questions in the field of unconventional superconductivity.
However, their synthesis poses considerable challenges, largely hindering
experimental research on this new class of oxide superconductors. That
synthesis is achieved in a two-step process that yields the most
thermodynamically stable perovskite phase first, then the infinite-layer phase
by topotactic reduction, the quality of the starting phase playing a crucial
role. Here, we report on reliable synthesis of superconducting infinite-layer
nickelate films after successive topochemical reductions of a parent perovskite
phase with nearly optimal stoichiometry. Careful analysis of the transport
properties of the incompletely reduced films reveals an improvement of the
strange metal behaviour of their normal state resistivity over subsequent
topochemical reductions, offering insight into the reduction process.
