Observation of Superconductivity Up to 8.7 K in Reduced Potassium Tantalate

Abstract The observation of superconductivity with a transition temperature ( T c ) up to 8.7 K in KTaO 3 single crystals annealed with CaH 2 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 K x TaO y (0.04 ≤ x ≤ 0.08, 1.24 ≤ y ≤ 1.35), depending on annealing conditions. Within the experimental ranges, the T c is peaked at x ≈0.05, and increases with decreasing y , and the highest T c is observed in K 0.05 TaO 1.24 . The T c observed here is much higher than that of KTaO 3 , 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 T c and its close connection with KTaO 3 and Ta, both of which are promising materials for quantum computing, make K x TaO y potentially interesting as a building block in constructing future superconducting quantum devices.