Investigations On Fabrication, Structure And Properties Of Perovskite Lead-Free Ferroelectric Materials

Up to present, the dominant piezoelectric materials are lead-based, represented (?)y Pb(Zr,Ti)O3(PZT) systems due to their excellent piezoelectric and (?)lectromechanical performances. However, these materials are harmful to the (?)nvironment and our physical health due to the large content of Pb, therefore, it is (?)uite necessary for us to develop the environmental-friendly lead-free piezoceramics (?)o replace or partially replace the lead-based piezoceramics.(1-x)Bi0.5Na05Ti03-xBaTi03(BNT-BT, BNT-xBT) based ceramics have been attracted oroad attention due to the good piezoelectric property with the composition around morphotropic phase boundary (MPB). In present work, two piezoelectric ceramic systems with large field-induced strain were designed and fabricated. The relationship between composition, structure and the electric properties was studies systematically. In addition, in order to promote the application of the lead-free piezoelectric ceramic in the MEMS devices, the lead-free ferroelectric thin films were also studied. The main results are as follows:1. Single ion Zr4+substituted (Bi0.5Nao5)0.93Ba0.07Ti1-xZrT03(BNBTZx) ceramics were fabricated. Elevating temperature and increasing Zr4+content are favorite to transform the long-range-order ferroelectric phase into short-range-order pseudocubic. Large strain response was obtained with the effective normalized strain d33*of465pm/V under4kV/mm at,x=0.014.2. Complex ions (Alo.5Nbo.5)4+substituted (Bi0.5Nb0.5)xO3 ceramics were fabricated. A largest quasi-static piezoelectric coefficient d33of210pC/N was obtained at x=0.01. Furthermore, at a critical composition x of0.02, targe strain response was obtained with the effective normalized strain d33*of575pm/V under5kV/mm, this was in the advanced level around the world.3. MPB BNT-BT and Mn-doped BNT-BT (BNBMT) thin films were prepared on Pt-electrodized Si substrate by using PLD method. A good ferroelectric property was obtained with the average remnant polarization Pr of11.3μC/cm2. The micro piezoelectric response shows that a large local strain response was obtained with the d33*up to92pm/V under12kV/mm. This was superior than other BNT-based lead-free films and also close to lead-based films.4. La0.7Ca0.3MnO3, La0.7Ba0.3MnO3and La0.6Sr0.4CoO3were introduced as buffer layers, who efficiently controlled the interface between BNBMT and substrate. Enhanced ferroelectric property was obtained with the saturated polarization Ps of50.3μC/cm2and remnant polarization Pr of20μC/cm2, comparable to those of its ceramic counterpart.5. Highly (100)-oriented films were prepared on the SrTiO3single-crystal substrate. Enhanced ferroelectric and dielectric properties were obtained with remnant polarization Pr of-21μC/cm2.