Conversion of 124 into 123 + CuO: microstructure and phase diagram

Abstract

Conversion of 124 into 123 + CuO is interesting because it can produce non‐superconducting CuO islands and highly strained local regions, both of which may act as flux pinning centers. Microstructural studies (TEM) show localized regions with high strain fields resulting from the lattice mismatch between 124 and 123 along the c axis. Enhanced Tc (95 K) was found in partly converted samples. The partial pressure of oxygen necessary for conversion from YBa2Cu4O8 (124) to YBa2Cu307 (123) decreases with decreasing temperatures, and below 850°C the boundary between 123 and 124 phase regions is found to fall approximately as log ρ(θ2) = 19.3 ‐22000/T. The phase diagram of the Y‐Ba‐Cu‐O system is given as a function of temperature and partial pressure of oxygen over the range between 500°C and 1000°C and 10‐6< P[O2] < 102 bar.

Application of High Temperature Electrochemical Techniques to YBa2Cu3 O 7 − y

“…Despite some variation, there is a general agreement on the low pressure decomposition reaction. According to the data of Tallon et al, 8 Morris et al, 27 and Bormann and Nolting, 9 the low pressure boundary for YBCO coincides with the CuO/Cu20 phase boundary. Schoch and Weppner ~7 reported a value of oxygen plateau at 700~ which lies on the CuO/Cu20 phase boundary.…”

“…The formation of 124 by a totally different reaction is investigated more extensively in the literature and is written as YBa2Cu3OT_y + CuO = YBa2Cu40 s [10] The results from Morris et al 27 and Karpinski 3~ are presented in Fig. 9.…”