Optical isotropy in polycrystalline Ba2TiSi2O8:: Testing the limits of a well established concept -: art. no. 184116

We report an optical properties investigation of randomly oriented polycrystalline solids with anisotropic crystal structure. Using fresnoite as the model material, we demonstrate several domain size effects, most notably that a cross-polarization response is observed for the case of large randomly oriented crystallites. We compare our measured results with simulations from several different dielectric models and demonstrate that the appropriate model depends upon the grain size. The results have important implications for the understanding of optical isotropy in polycrystalline materials and bulk vs nanoscale effects.