Nano Titanium Monoxide Crystals and Unusual Superconductivity at 11 K

Abstract

Nano TiO₂ is investigated intensely due to extraordinary photoelectric performances in photocatalysis, new-type solar cells, etc., but only very few synthesis and physical properties have been reported on nanostructured TiO or other low valent titanium-containing oxides. Here, a core–shell nanoparticle made of TiO core covered with a ≈5 nm shell of amorphous TiO_1+x is newly constructed via a controllable reduction method to synthesize nano TiO core and subsequent soft oxidation to form the shell (TiO_1+x). The physical properties measurements of electrical transport and magnetism indicate these TiO@TiO_1+x nanocrystals are a type-ІІ superconductor of a recorded T_c^onset = 11 K in the binary Ti–O system. This unusual superconductivity could be attributed to the interfacial effect due to the nearly linear gradient of O/Ti ratio across the outer amorphous layer. This novel synthetic method and enhanced superconductivity could open up possibilities in interface superconductivity of nanostructured composites with well-controlled interfaces.

Nano titanium monoxide with the crystalline core (TiO) covered with a ≈5 nm shell of amorphous TiO_1+x is the first time to be prepared and the highest T_c (11 K) in the binary Ti–O system is observed. Through controllable reduction and soft oxidation, the obtained sample is observed with nearly linear (1.0–1.9) variation of O/Ti ratio across the amorphous layer, suggesting a smooth interface which contributes to the unusual superconductivity.

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