Mechanism of liquid-phase epitaxy growth of NdBa₂Cu₃O_7−xfilm from low-peritectic-temperature YBa₂Cu₃O_7−xseed film

NdBa₂Cu₃O_7-x (NdBCO) superconducting films were successfully grown on MgO substrates by liquid-phase epitaxy (LPE) using YBa₂Cu₃O_7-x (YBCO) seed films which have lower peritectic temperatures. Microstructural characterizations using optical and electron microscopes revealed that most of the seed grains decomposed at the high processing temperature and dissolved when they touched the solution. The NdBCO grains were formed first by the quasi-homoepitaxial growth of NdBCO units on the few surviving YBCO seed grains and then grew pendently to cover the large bare surface areas of the MgO substrates quickly by lateral overgrowth. A micrometer-thick melt layer was entrapped between the film and the substrate. Through the few links provided by the surviving seed grains, a stable film/substrate orientation relationship could still be maintained. A semiquantitative analysis was done for the lateral overgrowth process, and two different lateral overgrowth stages were observed with about 50 times difference in the lateral overgrowth rate. Then, a semiquantitative understanding for the entire YBCO-seeded NdBCO LPE growth process was finally reached.