Mnco <sub> 3 </ Sub>-doped Aligned With The Phase Boundary 0.94bnt-0.06bt Lead-free Piezoelectric Ceramic Structure And Performance

There is a kind of high technical function materials, called piezoelectric ceramics which can transformate mechanical energy to electric energy or electric energy to mechanical energy. It is widely applied to electronic and micro-electronic equipments. The traditional piezoelectric ceramics can cause many environmental problems in applied process. So exploitation and study of lead-free piezoelectric ceramics have been becoming a focus home even all over the world.In recent years, people have widely studied several lead-piezoelectric ceramic systems with the most interest for example BaTiO3-based, Bi-layer structure, Bi0.5Na0.5TiO3-based, NaNbO3-based and tungsten bronze structure lead-free piezoelectric ceramics. Above all these kinds, Bi0.5Na0.5TiO3-BaTiO3(abbreviated to BNT-BT) system is called for a promising lead-free piezoelectric material. Nowadays, there are several modification ways, such as changing preparation, taking up or adoped some elements to it and modification of BNT ceramic by appending another structural ferroelectric properties or anti-ferroelectric ceramics to it, binary or muti-phases structural BNT-based solid solutions ceramics have been formed easily. Performances of 0.94Bio.5Nao.5Ti03-0.06BaTi03 are the best when it is near by the morphotropic phase boundary (abbreviated to MPB) at house temperature and piezoelectric strain constant d33 is 125pC/N.In this paper, we prepare the BNT-BT lead-free ceramics by conventional solid-state reaction system. We studied the effects of process conditions on the structure of ferroelectric ceramics 0.94BNT-0.06BT by XRD,SEM and other analytic system, and it is found that calcining temperature,sintering temperature and soaking time effect on the crystalline microstructures, and surface-structure. In this paper, XT200A digital balance made in Switzerland company are used to test the densities of samples in some different sintering temperature. The result showed that:(1) all the ceramics are single perovskite phase; (2) the best conditions of 0.94BNT-0.06BT ceramics prepared by conventional solid-state reach system are as follows:calcining temperature 840℃,sintering temperature 1130℃,soaking time 2.5h, (3) Sintering temperature can limit and complement soaking time and the last effects the later. If maintaining time is short, sintering temperature is high and vice visa. If soaking time is 2.5h,1120℃～1140℃is the proper range of sintering temperature. (4) when sintering temperature increase, The piezoelectric strain constant d33,dielectric constantεr,electromechanical coupling coefficient kp and mechanical quality factor Qm of all ceramic samples took on the trend:first increasing and then decreasing, but tanδtook on the trend correspondingly:first decreasing and then increasing. At 1130℃of sintering temperature, ρv=5.664g/cm3,εr=618.22,d33=122pC/N,tanδ=2.11%,Qm=205,kp=0.205.To improve the properties of 0.94BNT-0.06BT ceramics, it was studied particularly that addition effect on piezoelectric properties and dielectric properties of ceramics. In this paper, the 0.94Bi0.5Na0.5TiO3-0.06BaTiO3+x(wt%)MnCO3(x=0,0.2,0.3,0.4)lead-free ceramics were prepared by conventional solid-state reaction system. The effect on structure,piezoelectric and dielectric properties of 0.94BNT-0.06BT ceramics systems were studied particularly, including MnCO3 addition,preparation technique. The result of MnCO3 addition showed:sintering temperature rapidly drop when MnCO3 addition becoming high, which indicate that MnCO3 reduce its sintering temperature. XRD indicate that 0.94BNT-0.06BT with MnCO3 addition ceramics all take on single perovskite structure and second phase have not been found, which suggest that MnCO3 don't alter microstructures of 0.94BNT-0.06BT lead-free ceramics. The images of SEM indicate that 0.94BNT-0.06BT ceramic crystalline grains have obvious geometry appearance the interplanar interface is high-visible when MnCO3 is 0.3wt%. With MnCO3 increasing, the crystalline grain is large, and the ceramic particle's homogeneity is decreased. By the study of MnC03-doped 0.94BNT-0.06BT, results indicate that when MnCO3 increasing, density present this trend:first increasing and then decreasing. Density gets max 5.781g/cm3 when MnCO3 is 0.3wt%. Additional, the results also indicate that the piezoelectric strain constant d33,electromechanical coupling factor kp,dielectric constantεr have similar trend:first increasing and then decreasing With MnCO3 increasing. When MnCO3 is 0.3wt%, ceramics parameter reach the best value d33=159.4pC/N,kp=28.1%,εr=876.3, respectively. Dielectric loss present different change trend with MnCO3 increasing, first increasing, then decreasing, and last ascending.The mechanical quality factor Qm present reverse change trend:decreasing then increasing. When MnCO3 is 0.3wt%, Qm reach min value 152.Additional, large electromechanical coupling factor kp and electrical resistivity p could be obtained under low polar electric field (2.8kV) when MnCO3 were doped, which suggest that appropriate MnCO3 effectively reduce coercive electric field.