Determination of the thermal conductivity tensor of the n 7 Aurivillius phase Sr ₄Bi ₄Ti ₇O ₂₄

A challenge in the preparation of advanced materials that exist only as thin films is to establish their properties, particularly when the materials are of low symmetry or the tensor properties of interest are of high rank. Using Sr ₄Bi ₄Ti ₇O ₂₄ as an example, we show how the preparation of oriented epitaxial films of multiple orientations enables the thermal conductivity tensor of this tetragonal material with a c-axis length of 64.7 Å to be measured. The thermal conductivity tensor coefficients k ₃₃ 1.10 W m ^-1 K ^-1 and k ₁₁ k ₂₂ 1.80 W m ^-1 K ^-1 were determined by growing epitaxial Sr ₄Bi ₄Ti ₇O ₂₄ films on (100), (110), and (111) SrTiO ₃ substrates.