Phase stability and decomposition of superconductive YBa2Cu4O8

The stability of the YBa2Cu4O8 phase has been studied with respect to oxygen partial pressure P(O2 ) and temperature by x‐ray diffraction, thermogravimetry, and differential thermal analysis. The critical temperature Td for the decomposition of YBa2Cu4O8 phase was determined from thermal analyses. It was found that Td was strongly dependent on P(O2 ) and the following empirical relation was obtained: log[P(O2)(atm)]=12.41−(1.449×104)/Td(K). It was found that, when heated, YBa2Cu4O8 first decomposed into YBa2 Cu3.5 O7.5−z plus CuO for 0.02 atm<P(O2 )<9 atm, while for P(O2 )≤0.02 atm, it decomposed into YBa2Cu3O7−z plus CuO without yielding YBa2Cu3.5O7.5−z .

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