| Piezoelectric materials are such a kind of functional materials that can generate surface electric charge by exerting a mechanical stress on them, or can be deformed by exerting an electric field on them. The piezoelectric effect is an electromechanical coupling effect, the direct piezoelectric effect transforms mechanical energy into electric energy. Otherwise, the converse piezoelectric effect describes the strain developed in a piezoelectric material due to the displacement of the positive and negative electric charge center of gravity when an electric field is applied.The Aurivillius phase BLSF materials, possessing unique structure characteristics and high Curie temperature, have been given more attention. The bismuth layer-structured piezoelectric materials have been widely used in filter, energy transformation, high temperature and high frequency situations.Various Na0.5Bi4.5Ti4O15and Na0.5Bi2.5Nb2O9based high temperature bismuth piezoelectric ceramics were prepared by the conventional solid-state reaction technique. The physical properties were investigated in detail.1. A series of Na0.5Bi4.5TiO15piezoelectric ceramics with Ce modification were prepared, and the influence of Ce on dielectric and piezoelectric properties was investigated. The formula of the ceramics is Na0.5Bi4.5-xCexTi4O15(x=0.00,0.02,0.03,0.04)=(NaBi)0.5-x(NaCe)xBi4Ti4Oi5.It has been demonstrated that doping Ce into the ceramics is an effective way to improve their piezoactivity and thermal stability, meanwhile decrease their dielectric loss. Resistivity has been improved considerably, the problem of low electrical resistivity in high temperature use was resolved to a certain extent. For the modified Na0.5B4.5Ti4O15ceramic with x=0.03, it has the good piezoelectric properties of piezoelectric constant d33=26pC/N, planar electromechanical coupling coefficient kp=6%, thickness electromechanical coupling coefficient kt=29%, mechanical quality factor Qm=2769, dielectric loss tgδ=0.31%(measured at1kHz) at room temperature. 2. The Na0.5Bi4.5Ti4O15-based materials with different amounts of LiCe and A-site vacancy were prepared. The formula is (NaBi)0.5-x(LiCe)x/2[]x/2Bi4iTi4O15([] is [NaBi] vacancy; x=0.00,0.06,0.10,0.15). From the results of the temperature dependence of ε, it has been found that LiCe and vacancy additive has the effect to increase Curie temperature, meanwhile there was a apparent reduction of dielectric loss. For the modified Na0.5Bi4.5Ti4O15ceramic with x=0.10, it has the good piezoelectric properties of piezoelectric constant d33=28pC/N, planar electromechanical coupling coefficient kp=7%, thickness electromechanical coupling coefficient kt=25%, mechanical quality factor Qm=2693, dielectric loss tgS=0.20%(measured at1kHz) at room temperature.3. The LiCe A-site modified Na0.5Bi2.5Nb2O9piezoelectric ceramics were investigated. The formula is [(NaBi)1-x(LiCe)x]0.5Bi2Nb2C>9(x=0.00,0.04,0.06,0.08). The Curie temperature of the ceramics were slightly reduced under the influence of the small radius of Li and larger radius of Ce. For the modified Na0.5Bi2.5Nb2O9ceramic with x=0.06, The piezoelectric constant d33was improved to24pC/N(two times more than that of pure Na0.5Bi2.5Nb2O9), the planar electromechanical coupling coefficient kp was12%, the thickness electromechanical coupling coefficient kt was25%, the dielectric loss tgS has a value of0.26%(measured at1kHz) at room temperature. The experiment indicated that LiCe played a good role in improving the dielectric and piezoelectric properties of high temperature bismuth piezoelectric ceramics.4. The [(Nao.52Ko.42Lio.o6)Bi]o.5-x[]x/2(LiCe)x/2Bi2(Nb1.88Sbo.o6Tao.o6)09(x=0.00,0.04,0.06,0.08;[] is [NaBi] vacancy) piezoelectric ceramics were investigated. It has been found that the additive of LiCe and vacancy has a apparent effect to improve piezoactivity and decrease dielectric loss.The anisotropic characteristics were generally strengthened. The piezoelectric constants were all improved to two times or even more of the original. The dielectric loss has a maximum reduction of73%. For the modified ceramic with x=0.06, it has the good properties of d33=28pC/N, planar electromechanical coupling coefficient kp=7%, thickness electromechanical coupling coefficient kt,=28%, dielectric loss tgδ=0.72%(measured at1kHz) at room temperature. |
PDF Full Text Request