GROWTH MODE DEPENDENCE OF MICROSTRUCTURES AND SUPERCONDUCTING PROPERTIES OF ND1-XCU3OY THICK-FILMS PREPARED BY LIQUID-PHASE EPITAXY(XBA2)

We have prepared c-axis oriented Nd1+xBa2-xCu3Oy (Nd123) films onto Mg O(1 0 0) single-crystal substrates by the liquid-phase epitaxy (LPE) t echnique under two different modes of supersaturation. When the films are grown in the transient mode LPE (TMLE), the top surface of the fil ms is characterized by structures with step heights varying over sever al to some ten unit cells along the c-axis and with many small-angle t ilt boundaries. In contrast, when the films are grown in the step-cool ing mode, spiral steps with the height of a mono-unit cell are observe d at the top surface of the films and the number of small-angle tilt b oundaries is greatly reduced relative to that in the films grown by th e TMLE. The superconducting transition temperature Te of the films gro wn in the step-cooling mode reaches 93 K by annealing the films at 400 degrees C for 100 h in 10 atm O-2 atmosphere, whereas that of the fil ms grown in the TMLE is limited to 83 K. The less easy accommodation o f oxygen uptake but resulting better superconducting properties of the step-cooling film can be explained in terms of the compositionally we ll-ordered structure with less density of imperfections. (C) 1998 Else vier Science B.V. All rights reserved.