The O isotope effect of the ferromagnetic transition temperature was investigated in various samples of the manganite La0.8Ca0.2MnO3+δ, as a function of sintering conditions. Sintering at 1200C and above led to O-stoichiometric comparison samples with an isotope exponent of αO = 0.41, and transition temperatures TC(16) = 189K and TC(18) = 180K. Samples sintered at 1000C, and below, always had O excess. The O excess led to vacancies at the A (La,Ca) and B (Mn) sites, leading to a decrease in unit cell volume. The unit cell volume was identical for both isotopes, and this implied equal O content for the isotopic comparison samples. The isotope exponent αO for O excess samples was much larger than 0.4. Its value, as well as the transition temperature, TC, depended upon the Mn4+ concentration, as well as the defect structure induced by A and B sites vacancies.

Oxygen Isotope Effect in La0.8Ca0.2MnO3+δ and its Dependence upon Oxygen Stoichiometry. J.P.Franck, I.Isaac, D.D.Lawrie: Physical Review B, 2001, 64[21], 214412 (8pp)