123 + CuO → 124 conversion slowed by lanthanum substitution

Sinha, A. P. B. ; Singh, K. K. ; Morns, D. E. (1987) 123 + CuO → 124 conversion slowed by lanthanum substitution Physica C: Superconductivity, 292 (1-2). pp. 65-72. ISSN 0921-4534

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Official URL: http://www.sciencedirect.com/science/article/pii/S...

Related URL: http://dx.doi.org/10.1016/S0921-4534(97)01638-9


The rate of formation of YBa2Cu4O8 (124) by solid state reaction of YBa2Cu3O7-δ (123) with CuO is dramatically slowed by substitution of La 3+ at Ba2+ sites. This is not an ion size effect, since substitution of Sr2+ for Ba2+ does not reduce the 123 + CuO → 124 conversion rate. The reaction kinetics have been studied as a function of La concentration and oxygen pressure. Higher oxygen pressure enhances the formation rate of 124. This is expected because conversion to 124 involves oxygen uptake since 123 is oxygen deficient at the reaction temperature. The reverse reaction 124 → 123 + CuO has been studied by thermogravimetry; the rate of this decomposition reaction remains unaffected by La substitution.

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