Heat treatment influence on microstructure and properties of MgB2 superconductor

Study results of 1 mm diameter MgB2 superconductors fabricated by "powder in tube" method are presented. Ti and Nb were used as diffuse barriers materials. The mixture of magnesium and boron, powder of MgB2, and also mixture of magnesium, boron and MgB2 were used to form superconducting compound. Heat treatments in temperature range of 650-700 degrees C and 750-900 degrees C for 1h were conducted. It is established that 1 h heat treatment at 700 degrees C or 1 h at 900 degrees C heat treatment are sufficient for formation of MgB2 superconducting phase (T-e=38 K) in superconductors with titanium barrier and powder mixture of magnesium and boron or magnesium, boron and magnesium diboride. The T-e of in-situ process Nb - sheated superconductors was 37.6 K, the same T-e were measured for ex-situ superconductors heat treated at 900 degrees C for 1 h. The critical current measurement results of fabricated superconductors were presented, optimal heat treatment modes were determined for fabricated superconductors.