Effect of heat treatment of HoBa_2Cu_3O_(7-δ) ceramics superconductor synthesized from nano-coprecipitated powders

摘要

Nano-sized metal oxalate precursors was thermally treated and investigated to produce high temperature superconducting ceramics with a formula of HoBa_2Cu_3O_(7-)δ (Ho-123). The nano metal oxalate powders were subjected to different heat treatments at various temperatures for the phase formation study. The high-TC phase was observed for all samples as an evidence for the single step transition of (R-T) curves. The T_(C(R = 0)) for Ho123 is 91 K and 90 K for samples sintered at 920°C, 930°C and 88 K for samples sintered at 940°C and 950°C, respectively. XRD data showed single phase of an orthorhombic structure where a small amount of none superconducting phase Ho_2BaC_uO_5 (Ho211) phase was detected. The Ho211 phase was increased as sintering temperature increased due to the decomposition process and affected the transport properties. SEM micrographs showed large grain sizes that are randomly distributed. However, the grain size decreased as the sintering temperature increased which resulted in the formation of weak-links and hence decreases the transport properties. Using nano-sized metal oxalate precursors simplified the formation of HTSC materials with less processing temperatures which could be beneficial in superconducting tape industry. In addition, control of the sintering temperature lead to the formation of Ho123 phase with optimum amount of Ho211 phase which acts as pinning centers and improves the transport properties.