Microstructure of MgB₂ Films Deposited on YSZ/Hastelloy Substrate

Abstract

Microstructures of MgB₂ films on yttria-stabilized-zirconia (YSZ)/Hastelloy substrates were studied by analytical transmission electron microscopy. The MgB₂ films with Mg-rich compositions were fabricated by pulsed laser deposition followed by annealing at 600°C or 680°C under Ar atmosphere. Fine grains of MgB₂ and MgO crystals 5-30 nm in size that shows a good mutual connectivity are formed in the MgB₂ films. The MgB₂ films also form voids 5-100 nm in size that may contain amorphous or oxide phases. Two-dimensional elemental analyses revealed that Mg and O atoms are enriched near the MgB₂/YSZ interface. From a comparison in microstructures between the 600°C- and 680°C-annealed MgB₂ films, it is suggested that the films composed of finer grains of MgB₂ exhibit a higher critical current density under high magnetic fields.