| Summary: | <p>Several attempts to synthesize Li<small><sub>3</sub></small>OCl – a lithium-rich antiperovskite compound envisaged as a potential solid electrolyte material for lithium metal batteries – have been reported, but few have yielded convincing results. There are two key challenges associated with this synthesis: the thermodynamic instability of Li<small><sub>3</sub></small>OCl at room temperature and its extreme hygroscopicity. Therefore, the likelihood of inadvertently forming the structurally similar thermodynamically stable hydroxide halide compound Li<small><sub>2</sub></small>OHCl is very high. In this report, we demonstrate the stabilization of a small volume fraction of antiperovskite phase with the characteristics expected for Li<small><sub>3</sub></small>OCl in ∼0.5 to ∼1 μm films fabricated from a Li<small><sub>2</sub></small>O + LiCl powder target by RF magnetron sputtering. Measures were taken to minimize the presence of moisture at all stages of synthesis and characterization. X-ray diffraction (XRD) experiments showed that reaction between the precursor phases occurred within the growing films to form a volume of antiperovskite phase with an identical lattice parameter to that predicted for cubic Li<small><sub>3</sub></small>OCl. This antiperovskite phase decomposed into Li<small><sub>2</sub></small>O and LiCl upon annealing at moderate temperatures. Characterization by Fourier transform infrared spectroscopy (FT-IR) confirmed the absence of O–H bonding in the films, providing further evidence that the antiperovskite phase was Li<small><sub>3</sub></small>OCl rather than Li<small><sub>2</sub></small>OHCl. Deposition of films with similar thicknesses from an Li<small><sub>2</sub></small>OHCl powder target was also performed for comparison. While FT-IR results showed that O–H bonding was present in these films, a small volume fraction of an antiperovskite phase with identical lattice parameter to Li<small><sub>2</sub></small>OHCl was only detected after heating the films to ∼100 °C. Owing to the low phase purities of films deposited from both target types, the Li<small><sup>+</sup></small> conductivities were found to be on the order of 10<small><sup>−8</sup></small> S cm<small><sup>−1</sup></small>. For Li<small><sub>2</sub></small>OHCl in particular, it is expected that further optimization of the processing conditions will lead to a significant increase in Li<small><sup>+</sup></small> conductivity. This is the first reported attempt to synthesize lithium-rich antiperovskite compounds by RF magnetron sputtering.</p>
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