Dielectric properties of oligomeric diisocyanate based composites with barium titanate

A series of composites is synthesized on the basis of oligomeric diisocyanate with different contents of ferroelectric filler barium titanate (BaTiO$_3$). The dielectric performances of the obtained composites are found to follow extreme dependences on the filler content with a sharp minimum of the dielectric permittivity and maximum of the dielectric loss tangent at BaTiO$_3$ content 30 vol.%. The characterization of the composite layers by confocal microscopy revealed that the observed dependences of their dielectric properties upon the composition are determined by structural changes of the composites, including percolation, formation of a single infinite cluster and structures of matrix-island and chain types at certain critical concentrations.