Synthesis of Bulk Superconducting LiNbO${}_2$ Crystals through CaH${}_2$ Reduction

Abstract

We have synthesized layered superconducting LiNbO${}_2$ crystals through a bulk phase transformation from LiNbO${}_3$ single crystals via CaH${}_2$ reduction. As the Nb valence is reduced from 5+ to 3+, the material undergoes a structural transformation to the resulting product, LiNbO${}_2$, which is accompanied by metallic behavior and a superconducting transition, Tc onset, as high as 14.4 K. Secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS) show that the resulting phase is hole-doped through de-lithiation during the reduction. Magnetization and AC susceptibility measurements from a tunnel diode resonator confirm the bulk nature of superconductivity with a superconducting volume fraction of approximately 77% and an upper critical field approaching 26 T. Our study demonstrates extreme hydride reduction as an effective method to induce phase transformations with non-topotactic pathways and can be used to synthesize bulk materials with exotic properties.

17 main text pages, with 9 figures. Supporting information section which is 3 pages and 3 figures. v3 corrected minor typographical errors