CVD routes to MgB2 conductors

TL;DR

This paper presents a chemical vapor deposition (CVD) method for producing doped MgB2 superconducting wires with high critical current densities, highlighting the effects of titanium doping and the resulting microstructure.

Contribution

It introduces a CVD process for doping boron fibers with titanium to produce MgB2 conductors with enhanced superconducting properties and detailed microstructural analysis.

Findings

Achieved a critical current density of 5×10^6 A/cm^2 at 5K in MgB2 wires.

Discovered uniform Ti dispersion within grains without TiB2 precipitation on grain boundaries.

Compared microstructure of CVD-derived MgB2 with solid-state reaction samples.

Abstract

Processing methods are described for the development of magnesium diboride wire using the chemical vapor deposition (CVD) to produce long lengths of suitably doped starting boron fiber. It is found that titanium can be co-deposited with the boron to make long lengths of doped fiber that contain both TiB and TiB2. When this fiber is reacted in Mg vapor to transform boron into MgB2, the resulting conductor has a superconducting critical current density of about 5 times 10^6 A/cm^2 at 5K and self field. The critical current density at 25K and 1 Tesla is 10,000 A/cm^2. Using optical methods to define grain boundaries and energy dispersive X-rays to determine Ti and Mg concentration, these samples show a fine dispersion of $Ti$ through out the grains and no conspicuous precipitation of TiB2 on the MgB2 grain boundaries. This is to be contrasted with the precipitation of TiB2 on MgB2 grain boundaries observed for samples prepared by solid state reaction of Ti, Mg, and B powders. Introducing Ti impurities into the B during the CVD deposition of the B gives a distribution of TiB2 in the resulting MgB2 different from solid state reaction of powders.