Currently, MgB₂ wires made by the powder-in-tube (PIT) method are most often used in the construction and design of superconducting devices. In this work, we investigated the impact of heat treatment under both low and high isostatic pressures on the formation of a layered structure in PIT MgB₂ wires manufactured using the Mg coating method. The microstructure, chemical composition, and density of the obtained superconductive wires were investigated using scanning electron microscopy (SEM) with an energy-dispersive X-ray spectroscopy (EDS) analyzer and optical microscopy with Kameram CMOS software (version 2.11.5.6). Transport measurements of critical parameters were made by using the Physical Property Measurement System (PPMS) for 100 mA and 19 Hz in a perpendicular magnetic field. We observed that the Mg coating method can significantly reduce the reactions of B with the Fe sheath. Moreover, the shape, uniformity, and continuity of the layered structure (cracks, gaps) depend on the homogeneity of the B layer before the synthesis reaction. Additionally, the formation of a layered structure depends on the annealing temperature (for Mg in the liquid or solid-state), isostatic pressure, type of boron, and density of layer B before the synthesis reaction.

A novel type of superconducting joining technique has been introduced to join unreacted internal Mg diffusion (IMD) single-core MgB₂ wires. Our method is based on fabricating a small diameter joint mould obtained by deforming an Nb/Cu composite tube with a longitudinal semi-cylindrical Mg and B core into a thick round wire. The small diameter of the joint provided advantages such as rapid cooling, low resistance, and the unique core design inside the joint ensured a uniform MgB₂ phase formation. Scanning electron microscope analysis revealed that the IMD MgB₂ wires had excellent contact with the superconducting MgB₂ bulk material inside the joint. The joint resistance, calculated from the decay of the trapped magnetic field over time, is a quite low value of 6.44 × 10⁻¹⁶ Ω at 20 K. The transport critical current (I _c) of the joint is 62 A at 20 K under a self-magnetic field, and the n-value of the joint is 66 at 20 K under 1.5 T. The results showed that the I _c of our joint can be determined precisely, regardless of whether the magnetic field is applied from low to high or from high to low value during I–V measurements.