Synthesis of Bulk Superconducting LiNbO 2 Crystals Through CaH 2 Reduction

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, T c 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.