Observation of Superconductivity Up to 8.7 K in Reduced Potassium Tantalate

Abstract

AbstractThe observation of superconductivity with a transition temperature (Tc) up to 8.7 K in KTaO3 single crystals annealed with CaH2 at 900–1000 °C is reported. The superconductivity is confirmed by both resistance and magnetization measurements and is 3D in nature. Characterizations of X‐ray photoelectron spectroscopy, X‐ray diffraction, and scanning transmission electron microscopy reveal that it locates in a 1‐µm‐order‐thick polycrystalline surface layer that shows a rock‐salt type structure, with a lattice constant of 0.454 nm, and can be chemically identified as KxTaOy (0.04 ≤ x ≤ 0.08, 1.24 ≤ y ≤ 1.35), depending on annealing conditions. Within the experimental ranges, the Tc is peaked at x ≈0.05, and increases with decreasing y, and the highest Tc is observed in K0.05TaO1.24. The Tc observed here is much higher than that of KTaO3, Ta, and pure TaO, and is also one of the highest among of all the known oxide superconductors with the same rock‐salt structure. The rather high Tc and its close connection with KTaO3 and Ta, both of which are promising materials for quantum computing, make KxTaOy potentially interesting as a building block in constructing future superconducting quantum devices.