High-temperature phase relationships for YxNd1–xBa2Cu3Oy(0 ≤ x ≤ 0.5) superconductors via containerless processing

Abstract

This paper presents the results of drop-tube experiments performed on YxNd1–xBa2Cu3Oy (0 ≤ x ≤ 0.5) to understand some of the effects of partial substitutions of Nd for Y on the phase relationships in these systems at elevated temperatures. Powders from 50 to 100 μm in diameter were processed in pure O2 at furnace temperatures from 1400 to 1800 °C, every 25 °C. The resulting samples were examined microstructurally using scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy. Powder x-ray diffraction was performed for phase identification. It was verified that Nd substitution alters phase selection by introducing at least one new phase and allowing for solidification of the superconducting composition directly from the melt via undercooling to below the peritectic transformation temperature. In addition, solidification pathways are altered for samples processed at temperatures just below the liquidus temperature. Microstructural and x-ray diffraction evidence was used to map the liquidus with increasing Nd substitution. It was found that a minimum in this liquidus occurs at or near the composition Y0.1Nd0.9Ba2Cu3Ox and at a temperature of 1500 °C (±25 °C).