Growth of strongly biaxially aligned MgB2 thin films on sapphire by postannealing of amorphous precursors

MgB2 thin films were cold grown on sapphire substrates by pulsed laser depo sition followed by postannealing in mixed, reducing gas, Mg rich, Zr getter ed, environments (pO(2)similar to 10(-24) atm) at 750 and 950 degreesC. The films had T-c in the range 29-34 K, J(c) (20 K, H=0) in the range 3x10(4)- 3x10(5) A cm(-2), and irreversibility fields H-* at 20 K of 4-6.2 T. An inv erse correlation was found between T-c and H-*. The films had grain sizes o f similar to0.1-1 mum and a strong biaxial alignment was observed in the 95 0 degreesC annealed film. (111) oriented MgO was also observed. Mg coating of films during crystallization appeared to improve film T-c. (C) 2001 Amer ican Institute of Physics.