Determination of the thermal conductivity tensor of the n=7 Aurivillius phase Sr4Bi4Ti7024

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 angstrom to be measured. The thermal conductivity tensor coefficients k(33) = 1.10Wm(-1) K-1 and k(11) = k(22) = 1.80Wm(-1) K-1 were determined by growing epitaxial Sr4Bi4Ti7O24 films on (100), (110), and (111) SrTiO3 substrates. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733616]