Abstract
The melting temperature, Tm, of YBa2Cu3O7−x and GdBa2Cu3O7−x superconductor ceramic compounds has been measured by differential thermal analysis (DTA) over a large oxygen partial pressure range of five orders of magnitude (2·10−5 < PO2 < 1 bar). It is shown that the DTA peak and endset temperatures are closer to Tm than the onset temperature. Correct measurement of Tm requires low heating rates and subatmospheric pressure conditions to avoid temperature shifts due to local oxygen overpressure and kinetic effects.
Highlights
Thermal stability of cuprate superconductor ceramic compounds, RE1Ba2Cu3O7Àx (REBCO) (RE means “rare earth”), is limited by incongruent melting at Tm, according to reaction: RE1Ba2Cu3O7Àx/n RE2BaCuO5þL þ m O2; (1)where L is a liquid phase
Unless the metal ratio of samples is exactly 1/2/3 and no extra phases coexist with REBCO, melting occurs over a temperature range
Tm is better determined by TPEAK and TENDSET than TONSET
Summary
Thermal stability of cuprate superconductor ceramic compounds, RE1Ba2Cu3O7Àx (REBCO) (RE means “rare earth”), is limited by incongruent melting at Tm, according to reaction: RE1Ba2Cu3O7Àx/n RE2BaCuO5þL þ m O2; (1)where L is a liquid phase. Thermal stability of cuprate superconductor ceramic compounds, RE1Ba2Cu3O7Àx (REBCO) (RE means “rare earth”), is limited by incongruent melting at Tm, according to reaction: RE1Ba2Cu3O7Àx/n RE2BaCuO5þL þ m O2; (1). Tm constitutes an essential input to construct the ternary REO-BaO-CuO2-x phase diagram and so to control nucleation and growth phenomena for epitaxial thin film and coated conductors preparation [6,8,9]. Among REBCO high-temperature superconductors, YBa2Cu3O7Àx (YBCO) is the most extensively studied because of its high critical temperature of 92 K and because, when prepared in the form of thin film or coated conductor, it can carry high electric currents at high magnetic fields [10e12]. Its critical temperature is about 3 K higher [9,13], what opens the possibility of carrying higher electric currents than with YBCO
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