Preparation,Structure And Properties Of Piezoceramic With Directional Through-Pore And Its Composites

Lead zirconate titanate(PZT)ceramics possess high piezoelectric and dielectric properties,while their applications in acoustic transducer and medical diagnostic imaging equipment are limited by low hydrostatic figure of merit(HFOM)and high acoustic impedance(Z).A single piezoelectric material is difficult to obtain excellent comprehensive performance and meet the demand of many application fields.Hence,porous piezoelectric ceramics with air phase and piezoelectric composites with a second phase draw more attention because of their low density,high HFOM and low Z.According to the dimension of each phase,piezoelectric composites with two phases have many connectivity patterns.Among them,3–0 type,0–3 type,1–3 type,3–3 type and 2–2 type piezoelectric composites have been widely studied,while 3–1 type porous piezoelectric structure and piezoelectric composite still need further research.In this paper,3–1 type porous PZT ceramics with different pore size and ceramic wall thickness were prepared by adjusting the different initial solid content and freezing temperature of the freeze-casting process,and the effect of preparation process on pore structure was summarized.The relation between piezoelectric properties and pore structure was also studied.The piezoelectric coefficient(d33)shows a gradually increasing trend with the decreased pore size and wall thickness at the same time.And when the PZT volume fraction exceeds a certain value about 50%,the d33 of PZT ceramics with directional through-pore is higher than that of corresponding dense PZT ceramics and their ferroelectric properties are comparable.According to the grain orientation measurement of different sections and the observation of ferroelectric domain,this paper introduces the enhanced piezoelectric properties are due to a certain degree of grain orientation growth along the through-pore direction.In addition,the small domain size is also beneficial to the high piezoelectric coefficient.Based on the porous PZT ceramics with excellent piezoelectric properties,some 3-1 type composites were fabricated.3–1 type PZT/Epoxy piezoelectric composites were prepared by filling the through-pore with Epoxy with a coating immersion method,and showed better acoustic performance and mechanical strength than commercialized 1–3 type piezoelectric composites.Using a modified hot-pressing process,3–1 type PZT/PVDF composites with improved d33 compared with 3–1 type PZT/Epoxy composites were obtained.What's more,3–1 type PZT/Co Fe2O4 composites with cobalt ferrite(CFO)as the second phase show obvious magnetoelectric effect,indicating a new composite structure of magnetoelectric materials.In addition,with the development of lead-free based piezoelectric ceramics,in this paper,3–1 type porous barium titanate(BT)ceramics with fine crystalline were also been prepared by the freeze-casting process and a two-step sintering method.By adjusting the two-step sintering schedules,BT ceramics with the special pore structure possess comparable dielectric and piezoelectric properties with lead-based porous ceramics.The d33 of 3–1 type porous BT ceramics could reach 303 p C/N with the porosity is very high around 65%.The results give a positive validation to the previous conclusion that the 3–1 type porous structure is conducive to the improvement of the piezoelectric properties.