Niobium titanium alloy superconductor has been widely used among thousands of known superconductors due to its excellent comprehensive properties. It is a key material in the superconducting magnets for medical nuclear magnetic resonance and large scientific devices. Niobium titanium alloy is a typical binary alloy composed of transition group elements. In the previous study on the high-entropy alloy superconductor (TaNb)0.67(HfZrTi)0.33 composed of multiple transition metal elements, it was found that the alloy showed an unusually stable superconductivity under ultra-high pressure (the pressure above one million atmosphere is ultra-high pressure, 1 million atmosphere =100 GPa). Because niobium and titanium are the main components of this kind of high-entropy alloy, the study of superconductivity of niobium and titanium alloy under ultra-high pressure can deepen the understanding of the micro-mechanism of superconductivity of high-entropy alloy.
In this paper, the superconductivity of niobium titanium superconductor under ultra high pressure is systematically studied. It was found that niobium titanium alloy maintained zero-resistance superconductivity at pressures up to 261.7GPa, indicating that niobium titanium alloy is the most pressure-resistant superconductor known to date. This pressure is the highest superconductivity pressure reported. Under this pressure, the transition temperature of niobium titanium superconductor increased from 9.6K at atmospheric pressure to 19.1K, and the experimental results of high pressure magnetoresistance in Hefei strong magnetic field showed that the critical magnetic field increased from 15.4T to 19T at 211GPa and 1.8K temperature. This is the highest superconducting transition temperature and the highest critical magnetic field found in the transition metal-element alloy superconductor. The XRD results of Synchrotron radiation of Shanghai light source show that the crystal structure does not change under 200 GPa pressure, but its volume is compressed by about 43%.
The study reveals the made of the element of transition metal alloy superconductor in high pressure the superconductivity can resist deformation and stability of characteristics, it has to do with copper oxides and iron-based superconductors superconductivity sensitivity to the height of the volume change is in stark contrast, and after the transition metal elements also superconductors (valence electronic d in closed shells) of the superconducting transition temperature drop behavior are obviously different according to the volume compression.
