Reduced thermal conductivity by nanoscale intergrowths in perovskite like layered structure La₂Ti₂O₇

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 La₂Ti₂O₇. 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 La₂Ti₂O₇ 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 La₂Ti₂O₇ 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 La₂Ti₂O₇ and ∼0.93 W/m K for Ta doped La₂Ti₂O₇ at 573 K.