| Piezoelectric microenergy harvesters,which can convert ambient low frequency mechanical energy into usable electrical energy,have recently attracted extensive attention in the field of new energy and Internet of Things.BaTiO3?BT?-based ceramics are among the most promising lead-free replacements for lead-based Pb?Zr,Ti?O3 ceramics owing to the relatively good piezoelectric properties and temperature stability.However,BT-based ceramics have some issues,including low large hysteresis in strain-electric field curves and poor long-term reliability,which seriously restrict their applications in precisely controlled devices and energy harvesting systems.Hence,improving the electrical properties of BT-based piezoelectric ceramics has become an urgent and significant practical research topic.In this thesis,we regulated the phase structure,grain orientation,grain size,microstructure,domain structure,and polarization state?polarization direction and intensity?of A&B substituted(Ba0.95Ca0.05)(Ti0.94Zr0.06)O3?BCTZ?piezoelectric ceramics by chemical methods?doping modification?and physical methods?crystallographic texturing/domain engineering strategies?,and researched piezoelectric properties,fatigue-resistant behavior and energy-harvesting performance energy hearvisting in ceramics to resolve the above challenge.BCTZ piezoelectric ceramics with CuO as sintering aid were prepared by a conventional solid phase method.The phase structure,densification behavior,microstructure,domain structure,electrical properties,thermal stability and energy harvesting of ceramics were investigated systematically.The results show that CuO doping can significantly increase the density of ceramic samples to make the grain size smaller and more uniform,and reduce the domain size.As a consequence,the piezoelectricity,electromechanical conversion and energy harvesting characteristics were all improved.BCTZ ceramics with 0.5 mol%CuO exhibited good electrical properties:the piezoelectric coefficient d33424 pC/N and the electromechanical coupling coefficient kp0.53,the piezoelectric voltage coefficient g3315.7×10-3Vm/N and the transduction figure of merit d33?g336.7×10-12 m2/N.The degradation of piezoelectric ceramic properties during temperature rise was mainly related to changes in phase structure and domain structure.When the CuO doping amount was0.5 mol%,the BCTZ energy harvesters possessed a power density value of 1.76?W/mm3 at 10 m/s2,being?3.6 times higher than that achieved in the no-doping counterpart.We propose to integrate crystallographic texturing and domain engineering strategies into BT-based ceramics.[001]C grain-oriented BCTZ ceramics with a texture degree as high as 98.6%were synthesized by templated grain growth.The phase structure evolution,densification behavior,microstructure evolution,orientation behavior evolution and orientation growth mechanism of matrix powders in BCTZ ceramics were systematically studied.The growth mechanism of texture ceramics was clarified.The results show that TGG is closely related to microstructure connectivity.And the texture process of ceramics was mainly divided into three stages:nucleation of BT template,rapid growth of oriented grains and slow growth after collision of oriented grains.The electrical properties of highly oriented BCTZ ceramics were greatly improved.A very high piezoelectric coefficient d33 of 755pC/N,an extremely large piezoelectric strain coefficient d*33 of 2027 pm/V and an ultralow strain hysteresis Hs of 4.1%were simultaneously achieved,enabling more than 24 times enhancement in piezoelectric properties in comparison to the randomly oriented ones.These values are the best values ever reported on lead-free piezoceramics,and are even better than those of relaxor and PZT-based ceramics.Based on the requirement for practical applications of BCTZ piezoelectric ceramics,the fatigue behavior and energy harvesting of BCTZ ceramics were systematically studied.The results show that textured BCTZ ceramics have excellent endurance against electrical fatigues,compared with non-oriented ceramics.After 3.16×106bipolar cycles,the electrical properties of textured BCTZ ceramics was almost unchanged.The excellent electrical fatigue resistance of textured BCTZ ceramics was attributed to reduced domain sizes and defect/charge concentration at the domain boundaries,increased number of domain walls and piezoelectric anisotropy and enhanced the domain mobility by forming 4O domain configuration.In addition,textured energy harvesters developed based on the textured BCTZ ceramics fully utilized the piezoelectric anisotropy,engineering domain configuration and composite effect,giving high electromechanical properties and energy harvesting performance.The output power density has possessed?9.8 times enhancement compared to that of the non-textured counterpart.The power densities,which increased from 6.4 to 93.6?W/mm3 with increasing acceleration excitation from 10m/s2 to 50 m/s2,are much higher than those reported previously on lead-free energy harvesters.High energy harvesting properties of textured BCTZ ceramics originated from the anisotropy of piezoelectric ceramics,engineered domain structures,and complex structrural effect.This thesis research not only produced enviromnmental friendely high performance piezoelectric material,but also up a model texturing procedure for making lead-free piezoelectric materials.In addition,this study provides sets up experimental and theoretical support foundation for the design of high-performance lead-free piezoelectric energy harvesters in the future,providing reliable material assurance for the replacement of lead-based high-performance electronic components,so the results also and haves important value in certain engineering applications value. |
PDF Full Text Request