Piezoelectric property of sol-gel derived composite gels

Low-density piezoelectric alununosilicate ceramics were prepared by sol-gel technology. In order to reinforce the fragile aluminosilicate aerogels, the inorganic component was mixed with organic polymers (polyacrylic acid, polyvinyl acetate, polydimethylsiloxane) during the gelling process. The strength of the composite gels increases two- or threefold, the piezoelectricity of the composite gels changes variously depending on the organic polymers. The aerogel containing polyvinyl acetate shows negligible piezoelectricity. The use of polydimethylsiloxane decreases the piezoelectricity by 50%; polyacrylic acid increases it by 100%. The structure and the Al incorporation have strong effects on the piezoelectricity. The chemical structures of the composite gels were investigated by means of (27)Al and (29)Si MAS NMR. Except for the gel samples with PDMS, the porosity of hybrid gels diminishes.