Anisotropic thermal conductivity of the Aurivillus phase, bismuth titanate, (Bi4Ti3O12):: A natural nanostructured superlattice

The thermal conductivity of c-axis textured polycrystalline perovskite Bi(4)Ti(3)O(12) and random polycrystalline material is reported up to 1000 C. Based on measurements of the thermal diffusivity, density, and specific heat, the thermal conductivity is lower along the c-axis than in the a-b plane by almost a factor of 2, and the anisotropy persists up to at least 1000 C despite a change in the crystal structure at 675 C. The exceptionally low (1.0 W/mK), temperature-independent conductivity perpendicular to the perovskite layer structure is attributed to the density difference between the pseudoperovskite and fluorite blocks in the unit cell, forming a natural nanostructured superlattice. (C) 2008 American Institute of Physics.