Research On The Properties Of PZT/ZrO₂ Nano-composites Prepared By Precursor Method

PZT based piezoelectric ceramics are widely used in many fields. In order to meet the higher demands of mechanical and piezoelectric properties for modern application, PZT/ZrO₂ nano-composites were prepared by using precursor method. The mechanical properties of PZT ceramics were significantly improved by introducing small amount second-phase nano-size ZrO₂ particles, the piezoelectric properties can also be improved.As B-site precursor, (Zra+xTi1-a)0.98Nb0.02O₂.01+1.96x, Zra+xTi1-aO₂+2x, (Zra+xTi1-a)0.985Fe0.015O1.9925+1.97x was prepared by the polymeric method. The B-site precursor and PbCO₃ are synthesized into PZT powders by solid state reaction at 740℃for 4 h. The PZT powders are pure metastable perovskite lacking of Pb in A site, and TEM showed that the average particle size is less than 100 nm. The precipitated ZrO₂ particles will be packeted into PZT grain, so the intragranular-type PZT/ZrO₂ nano-composite piezoelectric ceramic successfully generated during the sintering process. It was by XRD, SEM, EDS, TEM analysis to found and confirmed that the tetragonal and monoclinic ZrO₂ particles exist inside PZT matrix. ZrO₂ nanoparticles about 40¹00 nm were found by TEM, The stress stripes and spots caused by martensitic transformation and thermal mismatch were found by TEM, also the phenomenon of domain broking and bending by ZrO₂ particles.Because the crack propagation energy were effectively absorbed by stress field, and the ZrO₂ particles had strengthened the grain PZT matrix boundary additionally, so PZT/ZrO₂ ceramics has been strengthened and toughened. SEM showed that the fracture mode changes from intergranular to intragranular with the increase the addition content of ZrO₂ Flexural strength and fracture toughness were significantly impoved with the increasing of ZrO₂, PZTN₂(x=0.05) sintered at 1260℃for 2 h has the higher flexural strength and fracture toughness of 141.6 Mpa and 2.3 Mpa m1/2. The piezoelectric performance of PZTN1, PZTN₂ and PZTP1 nanocomposited ceramics improved obviously by adding a small amount ZrO₂, these three systems all have the optimal piezoelectric performance when adding 2 mol% ZrO₂, further ZrO₂ addition leading poor piezoelectric performance. The main properties of PZTN₂ when x=0.00 and x=0.02 areε3T3/ε0=1464,tanδ=0.013,d33=246 pC N-1,Kp=0.50,Qm=88.2,σf =97.11Mpa,KIC=1.07 Mpa m1/2,of PZTN₂) areε3T3/ε0=1531,tanδ=0.013,d33=250 pC N-1,Kp=0.52,Qm=95.9,σf=116.27 Mpa,KIC=1.44 Mpa m1/2。The abnormal improvement of piezoelectric with small amount of ZrO₂ is releated with the stress. Comparative study on Nb-doped and iron-doped PZT/ZrO₂ ceramics was made. It is found that Nb doping can improve the dielectric properties of temperature stability, while enhancing dielectric diffuse and Fe inhibits PZT matrix grain growth while significantly enhance the value of Qm. when sintered at 1250℃for 2 h, the grain size of PZTN3 is more than 5μm, but for PZTF is less than 1μm. Compact PZTF ceramics can be achieved when sinter at or above 1180℃. The main piezoelectric properties for PZT/ZrO₂ nanocomposites sintered at 1230℃for 2h, for PZTN3(x=0.02) areε3T3/ε0=1864, tanδ=0.013, d33=377 pC N-1, Kp=0.59, Qm=97, d31= -156.4 pC N-1, K31=0.32, S1E1 =15.2×10-12 m2 N-1; for PZTF(x=0.02) are Tε33/ε0=1174, tanδ=0.006, d33=290 pC N-1,Kp=0.48, Qm=360, d31= -98.25 pC N-1, K31=0.28, S1E1 =12.2×10-12 m2 N-1.