Preparation And Properties Of Lead - Free Piezoelectric Ceramics With BaTiO 3

In this paper, two ways are taken to improve the properties of BaTiO3piezoceramics.First, the A and B site doped BaTiO3-based lead-free piezoceramics are fabricated by solidstatd reaction technique and the effect of isovalent ions or equivalent ions substitution onthe structure and electrical properties of piezoceramics are systemically inveastigated.Second, the fabrication of the process is modified. The effect of direct reaction sinteringmethod on the structure and properties of BaTiO3-based piezoceramics are researched. Themain results are listed below.1. The ions Ca2+、Sn4+and Zr4+that are isovalent with Ba2+and Ti4+are chosen to bedoped into BaTiO3. The structure and electrical properties of the doped ceramics areinvestigated. The ceramics doped with appropriate ions possess pure BaTiO3perovskitestructure. With increasing Ca2+content, the orthorhombic-tetragonal phase transitiontemperature (TO-T) gradually shifts to lower temperature and then decreases below roomtemperature. The Ca2+doping almost does not affect the Curie temperature (TC). Sn4+andZr4+have similar effects on the phase transition temperature. They both raise the TO-Tbutlower the TCseverely. The Ca2+and Sn4+codoping with appropriate proportion couldadjust the TO-Tof the ceramics to around room temperature. As at the O-T phase transitionregion where the Gibbs free energy surface flattens, the orthorhombic phase and tetragonalphase are similar stable and this means there are more directions for the spontaneouspolarization to switch to during the poling process. As a result the piezoelectricity of Ca2+and Sn4+codoped ceramics are improved. For example, the (Ba1-xCax)(Ti0.95Sn0.05)O3piezoceramics with x=0.02possess excellent piezoelectricity with pizoelectrical coefficientd33=464pC/N, planar electromechanical coupling factor kp=43.1%, the maximum phaseangle between the resonance and antiresonance peaks on the impedance-frequency curvesθm=85.9°; the (Ba0.9Ca0.1)(Ti1-xSnx)O3piezoceramics with x=0.06possess enhancedpiezoelectricity with d33=405pC/N, kp=43.2%. In addition the substitution of Sn4+decreases the Curie temperature with the rate of10℃/(1mol/%) and the (Ba0.9Ca0.1)(Ti1-xSnx)O3piezoceramics with x=0.1shows the typical characteristics ofrelaxor ferroelctrics with broadened dielectric peak and large diffusion index γ.2. The Y3+and Bi3+which have the different valent with Ba2+and Ti4+are respectivelydoped into Ba(Ti0.96Sn0.04)O3and Ba(Ti0.98Sn0.02)O3ceramics to enhance thepiezoelectricity of the ceramics. Y3+and Bi3+also can decrease theorthorhombic-tetragonal phase transition temperature TO-T. The codoping with Sn4+or Zr4+with appropriate proportion could adjust the TO-Tof the ceramics to around roomtemperature and enhance the piezoelectric performance of the ceramics at roomtemperature. For example, the Ba(Ti0.96Sn0.04)O3-xY2O3(x=0-0.4%) ceramic with x=0.2%possesses largest d33(454pC/N) and kp(43.1%); the Ba(Ti0.98Zr0.02)O3-xBi2O3ceramic withx=0.04%possess enhanced piezoelectric performance (d33=340pC/N, kp=43%). Y3+substitution monotonically increases the ceramics’ Curie temperature from74.1℃forcomposition x=0to93.6℃for composition x=0.4%and broadens the usage temperatureregion of the piezoceramics, which is very beneficial for the practical application.3.(Ba1-xCax)(Ti0.85Zr0.15)O3(x=0-0.15) lead-free piezoceramics are prepared by directreaction sintering method. The ceramics prepared by direct reaction sintering methodpossesse pure perovskite phase structure and dense microstructure. At x=0.15the samplepossesseslargest piezoelectric constant d33of208pC/N.