This work was funded by the Spanish Programa Nacional de Materiales through projects MAT2014-51778-C2-1-R and MAT2014-51778-C2-2-R. We also acknowledge: the Center of Excellence award Severo Ochoa SEV-2015-0496, SGR753 and SGR948 from the Generalitat of Catalunya and European Union through projects Eurotapes (EU-FP7 NMP-LA-2012-280432) and Ultrasupertape (ERC ADG-2014-669504). FT acknowledges financial support from USTO. The authors are indebted to Dr. Joan Pere López Olmedo and Dr. Xavier Fontrodona of STR, University of Girona, for their technical assistance.

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.

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