Synthesis of Bulk Superconducting LiNbO2 Crystals Through CaH2 Reduction.

We have synthesized layered superconducting LiNbO2 crystals through a bulk phase transformation from LiNbO3 single crystals via CaH2 reduction. As the Nb valence is reduced from 5+ to 3+, the material undergoes a structural transformation to the resulting product, LiNbO2, 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 ≈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-topochemical pathways and can be used to synthesize bulk materials with exotic properties.