Synthesis and Dielectric Characterization of Polystyrene Composites Containing Surface-Modified Titanates and Novel Mixed-Metal Phosphonates

This work reports on the synthesis and dielectric characterization of polystyrene composites containing a variety of titanates, aluminates, and novel mixed metal phosphonates. We investigated both micron-sized and nano-sized BaTiO₃ materials as well as a variety of covalently surface-modified BaTiO₃ to assess the effect of particle size and surface treatment on the composites' effective dielectric permittivity. Novel layered 1:1 mixed metal phosphonates, ATi(O₃PC₆H₅)₃ (A = Ba, Sr), were prepared via a hydrothermal route, in which mixed metal oxides, BaTiO₃ and SrTiO₃, were reacted with phenyl phosphonic acid. We also prepared LaAl(PPA)₃ from LaAlO₃ in the same way. In all cases, PS composites containing mixed metal phosphonates exhibited higher dielectric constants and lower dielectric loss values than PS composites containing the corresponding titanates or aluminates. The relatively high dielectric constant exhibited by the mixed metal phosphonates could be due to their organic-inorganic hybrid layered structures. This suggests the possibility that interfacial polarization changes could account for the relatively high dielectric constants of the mixed metal phosphonate systems.