Thermal conductivity of (La$_{0.25}$Pr$_{0.75}$)$_{0.7}$Ca$_{0.3}$MnO$_{3}$ under giant isotope effect conditions

The thermal conductivity of (La$_{0.25}$Pr$_{0.75}$)$_{0.7}$Ca$_{0.3}$MnO$_{3}$ manganite has been studied. The isotope substitution of $^{18}$O for $^{16}$O in this compound leads to a ferromagnetic-antiferromagnetic phase transition at low temperatures. It has been found that the thermal conductivity in the ferromagnetic state is approximately two times higher than in the antiferromagnetic state. It has been shown that the small value of thermal conductivity and its temperature dependence can be due to strong phonon scattering from crystal lattice defects, which are thought of as Jahn-Teller distortions. The parameters of this scattering can be determined within the Debye model of thermal conductivity from a comparison of samples differing in their isotope composition.