Formation of NdBa2Cu3O7−δ amorphous phase by combining aero-acoustic levitation and splat quenching

Abstract

Small spherical samples (diameter approximately 2 mm) of NdBa2Cu3O7−δ (Nd123) were fully melted in Ar gas flow in an aero-acoustic levitation device and subsequently rapidly cooled by splat quenching. For samples quenched above the liquidus, the microstructual and x-ray-diffraction (XRD) observations suggested the existence of the amorphous phase with small quantities of the BaCuO2 and BaCu2Ox. The high-temperature XRD results indicated that the decomposition of the amorphous phase, probably assisted by atmospheric CO2 and H2O, led to formation of the BaCO3 phase at 400 °C and, subsequently, the Nd123 phase was formed by the solid diffusion above 800 °C. Another set of Nd123 samples was fully melted in O2 gas flow, undercooled while levitated, and then splat quenched at a temperature below the peritectic temperature (TP). These samples possessed a microcrystalline microstructure of the Nd123 phase that was confirmed by XRD. This indicated that the Nd123 phase was solidified directly from the undercooled melt quenched below TP.