Growth and superconductivity of niobium titanium alloy thin films on strontium titanate (001) single-crystal substrates for superconducting joints

Abstract

Aiming to introduce NbTi alloy superconducting joints for REBa2Cu3O7−δ (REBCO, RE: rare-earth element) superconducting wires, NbTi alloy thin films were deposited at room temperature on SrTiO3 (STO) (001) single-crystal substrates, which have a high lattice matching with REBCO (001). The strain, crystallinity, surface morphology, and superconducting property of the films with various thicknesses were investigated. The NbTi films grew in the orientation with (110)NbTi//(001)STO:[001]NbTi and [11–0] NbTi//[100]STO; that is, the NbTi lattices had two directions in the (110) of NbTi. The strain decreased and the crystallinity improved as the film thickness increased. The films were found to crystallize immediately at the interface between the films and substrates by cross-sectional scanning transmission electron microscopy. The flat surfaces of the films have mesh-like morphologies due to the growth of elongated NbTi grains along the [100] and [010] of the STO, reflecting the in-plane two directions of the NbTi lattices. The superconducting transition temperature of the films increased with improvement in the crystallinity of the films. The preparation of superconducting NbTi alloy thin films with sufficient crystallinity at room temperature suggested the possibility of forming the films on REBCO and the applicability of the films as superconducting joints.

Relation between Crystal Structure and Transition Temperature of Superconducting Metals and Alloys

“…This is also manifested by the small range between 30% and 60%, where NbTi shows the best superconducting properties [72]. The problem is that there are not many reports in the literature concerning the crystal parameters of NbTi and the correlation to the superconducting transition temperature [70,72,73]. Thus, we employ here for an estimation the data of a wire manufacturer and the data of [74][75][76], with a = 0.3285 nm.…”

Preparation of Epitaxial NbTi Thin Films at Room Temperature and Elemental Technologies for Superconducting Joint

“…近年、高温超電導線材は次世代高磁場 MRI 用のコイル 線材としての利用が期待され、超電導接続技術の研究開発 が活発になっている [1][2][3][4][5][6][7][8][9][10] 。我々は、線材とは異なる異種超 電導体薄膜を用いた Indirect 超電導接続 1) の開発を進めて おり、室温により近い温度での薄膜接続により線材の超電 導特性の劣化を回避する手法を提唱している [11][12][13] 。…”

Fabrication and Characterization of High-Quality Epitaxial Nanocolumnar Niobium Films with Abrupt Interfaces on YSZ(001)

“…Manipulation of the phase, structure, properties, and phenomena at the nanoscale dimensions is critical to realize the full potential of electronic and photonic materials in many of today’s advanced technologies. In particular, highly ordered or engineered heterostructured epitaxial layers are becoming highly beneficial in many scientific/technological applications, such as integrated sensors, thin-film solar cells, optical filters, microelectromechanical systems, superconducting layers, electrocaloric devices, and photonic devices. − However, engineering such ordered structures with atomic scale precision and containing layers a few nanometers in thickness requires a very detailed, fundamental understanding of the crystallography, nanostructure, surface/interface chemistry, defect chemistry, and their evolution as a function of synthesis pathway. Revealing the structure–property relationship would allow for the fine-tuning of material properties for viable electronic device applications and exploring new electronic, magnetic, optical, and optoelectronic applications.…”

“…Nb also exhibits excellent physical and mechanical qualities. Its relatively low density, high Young’s modulus, and high yield strength, which are 8.6 g cm –3 , 103 GPa, and 240–550 N mm –2 , respectively, combined with its electronic properties, make Nb and Nb-based alloys suitable for applications, where materials and devices are often subjected to extreme environments, especially, elevated temperature or pressure or radiation or combination of these. ,− Unlike other refractory metals, Nb finds widespread applications in nanoelectronics and nanophotonics. Nb thin films and nanomaterials are popular for their utilization in nano-SQUID circuits for switches operating at high frequency under cryogenic conditions, superconductivity, single photon detectors, and high-temperature plasmonic applications .…”