MgB 2 and Mg 1− xAl xB 2 single crystals: high pressure growth and physical properties

Abstract

Single crystals of MgB 2 have been grown with a high pressure cubic anvil technique. They grow via the peritectic decomposition of the MgNB 9 ternary nitride. The crystals are of a size up to 2 × 1 × 0.1 mm 3 with a weight up to 230 μg. Typically they have transition temperatures between 38 and 38.6 K with a width of 0.3–0.5 K. Investigations of the P– T phase diagram prove that the MgB 2 phase is stable at least up to 2190 °C at high hydrostatic pressure in the presence of Mg vapor under high pressure. Substitution of aluminum for magnesium in single crystals leads to stepwise decrease of T c. This indicates a possible appearance of superstructures or phases with different T c's. The upper critical field decreases with Al doping.