Growth of strongly biaxially aligned MgB[sub 2] thin films on sapphire by postannealing of amorphous precursors.

MgB[sub 2] thin films were cold grown on sapphire substrates by pulsed laser deposition followed by postannealing in mixed, reducing gas, Mg rich, Zr gettered, environments (pO[sub 2] ∼ 10[sup -24] atm) at 750 and 950 °C. The films had T[sub c] in the range 29–34 K, J[sub c] (20 K, H = 0) in the range 3 × 10[sup 4] − 3 × 10[sup 5] A cm[sub -2], and irreversibility fields H* at 20 K of 4–6.2 T. An inverse correlation was found between T[sub c] and H*. The films had grain sizes of ∼0.1–1 µm and a strong biaxial alignment was observed in the 950 °C annealed film. (111) oriented MgO was also observed. Mg coating of films during crystallization appeared to improve film T[sub c]. [ABSTRACT FROM AUTHOR]