| We have originally found a kind of special piezoelectric polycrystalline materials(Applied Physics Letters,95,022904,2009).The polycrystalline ceramics which made by ordinary sintering technique have piezoelectric effect without polarization.Compared with the ordinary ferroelectric piezoelectric materials,a lower symmetry of piezoelectric tensors was found in these NBT-BT ceramics,and the macroscopic symmetry is generally described as∞mm, equivalent to the hexagonal polar crystal class6mm. The research suggests that the special piezoelectricity has no direct relation with the ferroelectricity.We carried a series of research about this new type of piezoelectric material s,basic material requirements,the natural polarity microscopic and macroscopic mechanism.1.Explore the self-poled BaTiO3basic perovskite.The major research is the BaTiO3-xBi2O3ceramic natural polarity. The BaTiO3ceramic powder were synthetized firstly,and they were mixed with Bi2O3in different molar radio,the radio is1:x.Using the ordinary sintering way, we prepared the self-poled BaTiO3ceramic.The experiment results show that, this kind of natural polarity ceramics have normal and reverse piezoelectric effect without polarization,the normal piezoelectric effect parameter d33max. is.11PC/N,and the piezoelectricity will not disappear when the temperature higher than the phase transition point,When the samples(x=0.25) sintered at880℃,they have piezoelectricity, but at1100℃, the piezoelectricity disappears.The XRD shows that the self-poled samples main phases are BaTiO3and Bi12TiO20.By combining Raman spectroscopy and x-ray photoelectron spectroscopy techniques,we have identified the polarization has relation to the expanded BiO5an slightly distorted TiO6units in the BaTiO3-Bii2TiO20ceramic. 2. The self-poled ceramics which BaTiO3and Bi12TiO20mixed directly have been studied in this part. First of all, a large proportion of BaTiO3and Bi12TiO20can make self-poled ceramics, and the strength firstly increases and then reduced.We select the BaTiO3-0.083Bi12TiO20samples, as you can see, the Raman spectrum peaks, relative to Bi12TiO20ceramic standard peak, shift to lower wave numbers.This result is similar to the the conclusion of the first part,so we conclude that there are amorphous phases formation; the low wave number peaks (P1-P14) are related to the BiOs structure,it states that the specific distortions appears in this polyhedron. By Raman spectroscopy and XPS study,we speculate that the natural polarity may relate to the distorted BiOs polyhedron and the TiO6polyhedron.Through the DSC(Differential Scanning Calorimetry) analysis, the samples sintering temperature is at the Bi12TiO20melting state.This solid-liquid state offer a macroscopic force in the interface, the force maybe the cause of macpolarity.The macroscopic polarization maybe due to the partial alignment of these distorted units located within the grain boundary amorphous phases.3. Research the polarity of theBa(Zrx,Ti1-x)O3-yBi12TiO20and the Ba(Sn,Ti)O3-y Bi12TiO20self-poled ceramic.Firstly,we synthesized the pure phase different proportions of Ba(Zrx,Ti1-x)O3, through XRD, we see that it can synthesize the pure phase Ba (Zrx, Ti1-X) O3(x=0.25, x=0.50, x=1), and through the dielectric temperature spectrum we can see transformation temperature are moved to a room temperature, at room temperature, the structure is cubic phase. For piezoelectric properties, in Zr gradually replace Ti process,the natural polarity still exist, but the piezoelectric activity declines, when x=1, natural polarity disappears. And we found natural polarity has a certain relationship with temperature gradient by annealing, the solid liquid interface state make polarization produced. Then synthetized Ba (Snx, Ti1-x) O3(x=0.25, x=0.50, x=1), with certain proportion mixing Bi12TiO20and found this natural polarity phenomenon in the pure phase BaSnO3based perovskite structure, further expand the self-poled ceramic range. |
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