Study On The Properties Of Na_0.5Bi_0.5TiO₃-based Ceramics And Its Application On The Filters

In this paper, effects of various dopants on the electric properties of NBT-basedlead-free ceramics were investigated. The properties of lead-free filter made by thematerial of (Na_1-xK_x)_0.5Bi(0.5)TiO₃-Mn were studied.Firstly, lead-free piezoelectric ceramics 0.92(Bi_0.5Na_0.5) TiO₃-0.08BaTiO₃+x at.%Co³⁺(abbreviated as BNBT-Co, with x ranged from 0 to 8mol%) were prepared by thesolid state reaction method. Effects of the amount of Co³⁺ on the electrical properties andphase transition have been studied. The results indicate that the addition of Co³⁺enhances the mechanical quality factor Q_m significantly, whereas piezoelectric constantd₃₃, dissipation factor tanδand planar electromechanical coupling k_p decrease withincreased amount of Co³⁺. 0.92(Bi_0.5Na(0.5)) TiO₃-0.08BaTiO₃+3.5at.% Co³⁺ ceramicsexhibit good performance with mechanical quality factor Q_m=910, piezoelectricconstant d₃₃=106 pC/N, planar electromechanical coupling k_p=10% and dissipationfactor tanδ=1.1% at lkHz. Compared to the pure BNBT ceramics, the first dielectricpeak T_d disappeared after the addition of Co³⁺, which means that the transition offerroelectric phase to antiferroelectric phase has been eliminated.Secondly, Effects of Sm³⁺ doping on the crystallogram, microstructure andpiezoelectric properties of 0.94(Bi_0.5Na_0.5) TiO₃-0.06BaTiO₃ were studied. The XRDshows all of the samples exhibit single perovskite phase and The SEM indicated thatgrain sizes of BNBT were restrained in a certain extent after the addition of Sm³⁺. Thevariation of the piezoelectric properties suggests that proper amount of Sm³⁺ can reducethe dissipation factor tanδ.Lastly, effects of Mn-doped (Na_1.xK_x)_0.5Bi_0.5TiO₃ on the piezoelectric properties thelead-free middle frequency ceramic filters developed by this material were investigated.The properties of (Na_1-xK_x)_0.5Bi_0.5TiO₃ were improved by the doping of Mn. At the0.3%(wt) Mn-doping level, the ceramics exhibit good performance with d₃₃=135pC/N,kp=31%, Q_m=183. Using the thickness vibration mode of the resonance samples, themulti-section filters with center frequency is about 520 kHz were fabricated. Through thesuitable combination, the filters have good choose character with the loss insertion nomore than 5dB and the out-band attenuation more than 30dB.