The Preparation And Investigation Of Large-strain Piezoelectric Ceramics

In this paper, piezoelectric ceramics were prepared through a traditional solidsolution method to achieve large-strain application. PLZT-PZN possesses extremelyhigh piezoelectric properties, however, the introduction of La3+leads to obviousdecrease of Curie temperature (Tc). According to previous research, PZN possesseshigh Tc=140°C. But the formation of pyrochlore phase, which will seriouslydecrease piezoelectric performance, is unavoidable when using traditional solidsolution method. PZT-PNN system exhibits extremely high piezoelectric propertiesbut the Tcof PNN is-120°C. The combination of PZN and PNN is promising to meetthe requirements of large-strain piezoelectric ceramics.0.7PZT-xPZN-(0.3-x)PNN (x=0.07,0.10,0.07,0.10,0.20) ceramics were synthesized through traditional solidsolution method and optimal piezoelectric d33was550pC/N when PZN contentreached10mol%. MPB was determined to be between45/55and46/54, and the bestproperties: d33=550-570pC/N, Tc=252°C, tanδ=1.45-1.65%.The piezoelectric properties obviously increased when using new sinteringmethod which effectively improved the concentration of Pb atmosphere. The bestmolding and poling conditions: dry pressing with400MPa, poled in silicone oil bathunder2.7kV/mm DC field at120°C for10-15min. The ceramics sintered at1180°Cwith composition Zr/Ti=46/54possessed optimal piezoelectric and dielectricproperties: d33≈640pC/N, ε33T/ε0≈3300, tanδ≈1.85%, Kp=0.655, Tc=272°C.The XRD analysis confirmed the MPB composition. SEM results showed that thesintering temperature had significant influence on grain size. Smaller grain sizehelped to improve the aging performance of ceramics because of the pinning effect ofnumerous grain boundaries.Bipolar S-E loops showed that0.7PZT-0.1PZN-0.2PNN system possessed veryhigh field-induced strain:0.26%under alternating electric field of0.8kV/mm and0.45%under3.0kV/mm. Ecdecreased with the increase of Zr/Ti ratio, Smaxmaintained at high level for tetragonal-rich phase near the MPB composition and thensharply decreased when the composition changed to rhombohedron phase. UnipolarS-E loops showed that the system had low strain hysteresis, suitable for large-straindriving applications. Specimens with MPB composition sintered at1180°C possessed high Curie temperature (Tc=272°C) and smaller grain size, thus excellent polingstate could be maintained after long-time depoling treatment. A large d33of570pC/Nwas obtained when the depoling temperature reached180°C, indicating that thesystem can be used as large-strain materials at high temperature.B-site oxide precursor method was also used to synthesize0.7PZT-0.1PZN-0.2PNN ceramics. The result showed that pure perovskite structureand relatively high properties were obtained. The synthesizing temperature of B-siteoxide precursor was much lower compared to present reports, which deserved furtherexploration.In conclusion, this paper reported an optimal composition0.7PZT-0.1PZN-0.2PNN (Zr/Ti=46/54) and large d33, high Tc, excellent Kp, high Ec,considerable field-induced strain and small tanδ, low strain hysteresis were obtaind atthe same time for ceramics sintered at1180°C. In addition, small grain sizeeffectively improved the aging performance and helped to maintain excellent polingstate at high temperature. The system was promising to be used as large-strainmaterials in a wide temperature range.