Co-doping And Properties Of CaBi₄Ti₄O₁₅ Materials

Environmentally friendly lead-free piezoelectric ceramics with good properties and hightemperature resistance are urgently demanded due to the damage to the environment andhealth of human being resulting from the use of the traditional lead-based piezoelectricceramics and low operating temperature. Bismuth layer-structured ferroelectrics (BLSFs)ceramics become the potential candidate in piezoelectric device, especially at hightemperatures and high frequencies application, because of their relatively high Curietemperatures, low dielectric dissipation factors, low aging rate, high dielectric breakdownstrengths, larger anisotropy of electromechanical coupling factors and low temperaturecoefficients of resonant frequency. These materials suffer from some difficulty in poling andhave low piezoelectric activity because of their unique crystal structures. The volatilization ofBi2O3during sintering and the random arrangement of plate-like crystal grains are alsounfavorable factors to achieve high density and good properties.In this paper, conventional solid state reaction route is employed to fabricate CaBi4Ti4O15–based ceramics. Firstly, the effect of the co-doping of A/B sites on crystalline phase,microstructures, dielectric and piezoelectric properties of CaBi4Ti4O15ceramics isinvestigated, via the substitution of rare earth metal ions Y3+and Eu3+ions for Ca2+ions on Asite, and V5+for Ti4+on B site. Secondly, the structures, dielectric and piezolectric propertiesof composite materials are investigated by co-firing perovskite lead-free piezoelectricceramics K0.48Na0.52NbO3, Na0.5Bi0.5TiO3and BLSF Bi3.25La0.75Ti3O12with CaBi4Ti4O15materials.The composition of the substitution of ions in the A/B sites of CBT ceramics is representedas Ca1-xYxBi4Ti4-yVyO15+x/2+y/2（x=0~0.1, y=0、0.075）（CYBTV） andCa1-xEuxBi4Ti4-yVyO15+x/2+y/2（x=0~0.1, y=0、0.075）（CEBTV）. The co-doping of ions in theA and B sites results in the lattice distortion and improved microstructure, therefore,resistivity of grain increases and dielectric loss at high temperatures decreases, and Curietemperature increases as well. The co-doping of ions in the A and B sites has a remarkableeffect on the improvement of piezoelectric properties, and piezoelectric constant of ceramicsmore than doubles.Composite ceramics,（1-x）CaBi4Ti4O15-xK0.48Na0.52NbO3（CBT-KNN，x=0~0.4）and（1-x）CaBi4Ti4O15-xNa0.5Bi0.5TiO3（CBT-NBT，x=0~0.4）are investigated for the first time.The stable bismuth layered structure is formed by co-firing CBT with suitable amount of perovskite materials KNN and NBT. With the increase of KNN and NBT, the Curietemperature decreased slightly and dielectric loss at high temperatures decreases sharply,meanwhile, the dispersion of ferroelectric-paraelectric phase transition enhangces andpiezolectric properties increase. Small amount of second phase appears and ceramic densitydecreases with more addition of KNN and NBT.Intergrowth materials,（1-x）CaBi4Ti4O15-xBi3.25La0.75Ti3O12（CBT-BLT, x=0~1）, aresystemically investigated. A single bismuth layered structure has been formed via cofiringCBT with BLT. The Curie temperatures of the intergrowth materials are between those of theCBT and BIT, and dielectric loss is less than both of them. Voltage resistance increases bydoping suitable amount of BLT, which is helpful in polarization process. When the amount ofBLT x=0.3, both d33and Kp achieve the maximum values with a d33of21and a Kpof0.09.