Processing And Properties Of PZT/ZrO₂ Piezoelectric Ceramic Composites Prepared By B-site Precursor Method

Metastable PZT solid solution powders of perovskite structure are synthesized by B-site precursor method at 750℃. With the increase of temperature, addition of ZrO₂ will precipitate from matrix of PZT because of systems becoming more stable state in thermodynamics, thus PZT/ZrO₂ Piezoelectric ceramic composite was prepared. The effect of ZrO₂ addition on mechanical and piezoelectric properties of composites was investigated in different ferroelectric areas from rhombohedral phase to tetragonal phase and Nb5+ ion-doped.Precipitated temperature, range, micrographs of ZrO₂ second phase were studied by using analysis methods such as XRD, SEM, TEM, EDS etc. The results showed that monoclinic or tetragonal zirconia presented when nominal addition of ZrO₂ over 0.03mol/PZNT mol by using XRD studies. There is no zirconia phase in pure PZT (Zr/Ti=60/40) sintering at 1260℃until nominal addition of ZrO₂ over 0.05 mol/PZT. From above we can see that a certain shift of Zr/Ti happened because of tolerance of Pb absence in PZT.The change of electric properties is up to PZT self when the shift of Zr/Ti happened. Electric properties such as d₃₃ and K_p have a little decrease due to the second phase of ZrO₂, but the value of d₃₃ at a=0.05 reaches the ninety percent of the value at a=0.00. Fracture toughness K_IC increases in both rhombohedral phase (62%) and tetragonal phase (14%) with the increase of ZrO₂ nominal value a. The bigger extent of increase in rhombohedral phase is the presence of tetragonal ZrO₂. Fracture strengthσf also increased except in tetragonal phase, this is related to the density and grain size and so on.There is thermal stress in sintering body because of the mismatch of physical properties such as elastic modulus or poisson ratio between matrix and particle. Compressive stress in PZT matrix and tensile stress in ZrO₂ particle, but real instance is decided to the precipitation state of ZrO₂. For example, Curie temperature decreased when Zr/Ti is 58/42, but increased when Zr/Ti is 51/49. The reason of increase can be explained of martensitic transformation or stress release.Dielectric temperature spectra showed that the degree of dispersion enhanced in tetragonal ferroelectric phase and weakened in rhombohedral ferroelectric phase when ZrO₂ can be seen evidently.