Sodium Bismuth Titanate Based Lead-free Piezoelectric Ceramics Doped

BNT piezoelectric ceramics are interested because of their good properties, such as relative larger piezoelectricity, high Curie temperature, free control for toxic atmosphere during the sintering and so on. However, pure BNT ceramics are scarce in still works because of difficulties to pole this ceramic, and show property of a large polarization.On the other hand, the BNT ceramic needs to a high sintering temperature.Thus must through doping modification to get some practicality ceramic materials in order to have it applied extensively in the field of industry. At present, the investigation of modification of BNT ceramic as follows: changing preparation, substitution or addition with other elements and modification of BNT ceramic through appending another structural ferioelectric or anti-feroelectric ceramics to it to form binary or muti-phases structural BNT-based solid solutions. In this paper, BNT-based piezoceramics by doping different elements ,such as Li,K,Mg,Zr and so on, into different lattice sites were studied . The effects of doping elements on structure and properties of BNT-based ceramic were studied. Some BNT-based ceramics with good electrical properties are got.0. 94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃(NBTB T)lead-free ceramics modified with different amount of MgO were prepared by the conventional ceramic fabrication technique. Microstructures were studied with x-ray diffraction, scanning electron microscope etc. Dielectric, piezoelectric properties were measured by digital electron bridge, d₃₃ meter, impedance analyzer etc, and the relationships between properties and structures were discussed. Measurement and analyse of BNT ceramic doped by Mg show that proper amount of MgO doped into ceramic is helpful for the sintering of samples and grain growth, thus it could improve the density of effective charge in the inside of ceramic which is manifestied by the aggrandizement of dielectric constant. Mg ions with the value of +2 diffused into A-site of the lattice resulting in "softe doping"effects and "particle size" effect. The super electric properties have been acquired at 0.3wt% MgO, piezoelectric constant up to 127pC/N; Planar electromechanical coupling factor up to 0.271; dielectric constant up to 919.96.Substituent of Ti⁴⁺ with Zr⁴⁺ in BNTBT ceramics are also studied.Result revealed that piezoelectricity of samples is improved because of lattic deformation of BNTBT ceramics which is caused by the difference of radius between Zr⁴⁺ and Ti⁴⁺. Thus the swerve 90°of domain is more easy in the course of polarization. At the same time, dielectric constant increases with the increase of the amount of Zr.Under the optimal conditions,doped BNTBTceramics with electric constant of 1395.141 was obtained. However, Curie temperature decreases with the amount of Zr replacing Ti.BNKLT-BZT binary systerm ceramics were investigated in this paper completely. When 0.006≤x≤0.1, Morphotropic phase boundary of ceramics was confirmed in the course of investigating the relationship between composition or structures and electrical properties according to x-ray diffraction and measurement of electrical properties. The maximum of piezoelectric constant d33(136pC/N)was obtained for the ceramic with x=0.1 and the maximum of planar electromechanical coupling factor up to 0.238 with x=0.008. At the same time, broader Curie temperature zone was found according to temperature dependence of dielectric constant of BNTBZT ceramics. This is most important for designing new NBT based on lead-free materials in the future.