Reduced thermal conductivity by nanoscale intergrowths in perovskite like layered structure La_2Ti_2O_7

摘要

The effect of substitution and oxidation-reduction on the thermal conductivity of perovskite-like layered structure (PLS) ceramics was investigated in relation to mass contrast and non-stoichiometry. Sr (acceptor) was substituted on the A site, while Ta (donor) was substituted on the B site of La_2Ti_2O_7. Substitution in PLS materials creates atomic scale disorders to accommodate the non-stoichiometry. High resolution transmission electron microscopy and X ray diffraction revealed that acceptor substitution in La_2Ti_2O_7 produced nanoscale intergrowths of n = 5 layered phase, while donor substitution produced nanoscale intergrowths of n = 3 layered phase. As a result of these nanoscale intergrowths, the thermal conductivity value reduced by as much as ～20%. Pure La_2Ti_2O_7 has a thermal conductivity value of ～1.3 W/m K which dropped to a value of ～1.12 W/m K for Sr doped La_2Ti_2O_7 and ～0.93 W/m K for Ta doped La_2Ti_2O_7 at 573 K.