Dielectric composite materials and method for preparing
The invention allows the fabrication of small, dense beads of dielectric materials with selected compositions, which are incorporated into a polymeric matrix for use in capacitors, filters, and the like. A porous, generally spherical bead of hydrous metal oxide containing titanium or zirconium is made by a sol-gel process to form a substantially rigid bead having a generally fine crystallite size and correspondingly finely distributed internal porosity. The resulting gel bead may be washed and hydrothermally reacted with a soluble alkaline earth salt (typically Ba or Sr) at elevated temperature and pressure to convert the bead into a mixed hydrous titanium- or zirconium-alkaline earth oxide while retaining the generally spherical shape. Alternatively, the gel bead may be made by coprecipitation. This mixed oxide bead is then washed, dried and calcined to produce the desired (BaTiO3, PbTiO3, SrZrO3) structure. The sintered beads are incorporated into a selected polymer matrix. The resulting dielectric composite material may be electrically &#8220;poled&#8221; if desired.
UT-Battelle, LLC E. I. Dupont de Nemours and Company
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Jack L. John J. Robert J. Kimberly K. Frederick C.
Collins Felten Lauf Anderson Montgomery