Determination of the thermal conductivity tensor of the n = 7 Aurivillius phase Sr₄Bi₄Ti₇O₂₄

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 Sr₄Bi₄Ti₇O₂₄ 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 k₃₃ = 1.10 W m⁻¹ K⁻¹ and k₁₁ = k₂₂ = 1.80 W m⁻¹ K⁻¹ were determined by growing epitaxial Sr₄Bi₄Ti₇O₂₄ films on (100), (110), and (111) SrTiO₃ substrates.