The piezoelectric phenomenon and the piezoelectric effect are that the electronic transducer piezo ceramics column exerts a pressure perpendicular to the electrode surface, which causes deformation and also generates a high voltage discharge. An audible alternating voltage signal is applied to the piezoelectric buzzer electrode, which produces a deformation and also produces an audible sound. By summarizing these similar phenomena, the concept of positive and negative piezoelectric effects can be obtained, that is, the effect of piezoelectric ceramics due to deformation of force is called positive piezoelectric effect. The effect of piezoelectric ceramics being deformed by the application of a voltage is called an inverse piezoelectric effect.
The internal structure of Pzt ceramic transducers is the material knowledge that tells us that the properties of any material are determined by its internal structure. Therefore, to understand the piezoelectric principle of piezoelectric ceramics and to understand the causes of piezoelectric effects, we must first know the piezoelectric ceramics. Cell structure and spontaneous polarization of piezoelectric ceramics have cell structure,which is the most widely used piezoelectric ceramic perovskite (CaTiO3) type structure, such as PbTiO3, BaTiO3, KxNa1-xNbO3, Pb (ZrxTi1-x ) O3 and so on. The chemical formula of this type of material is ABO3. In the formula, the electricity price of A is 1 or 2, and the electricity price of B is 4 or 5. Its unit cell (structural unit in the crystal lattice).
Formation of piezoelectric domains of piezoelectric ceramics:
A region in which the spontaneous polarization is uniform in the piezoelectric ceramic is called a domain (or a ferroelectric domain). The following is an example in which a perovskite structure is changed from a cubic phase to a tetragonal phase to illustrate the formation of domains.
1 c-axis direction determines spontaneous polarization orientation When the internal structure of the grain in the piezoceramic ceramic transducer changes from a cubic phase to a tetragonal phase, any one of the axes may become the c-axis of the tetragonal phase. Since the spontaneous polarization is parallel to the c-axis, the spontaneous polarization orientations of the respective unit cells may be different from each other. But this is not the lowest energy state.
2 The principle of minimum energy determines the domain structure,In order to meet the principle of minimum energy, the tetragonal phase grains must form a domain structure, and the lattice matching requires the unit cell to spontaneously polarize the orientation. The minimum energy existence principle of the cell requires the matching of the spontaneous polarization orientation inconsistent cells.
3.phase structure determines the type of domain wall Moreover, since the pizoelectric ceramics cell is tetragonal, the orientation of spontaneous polarization can only be parallel to one of the three crystal axes of the original reaction cubic phase, so the spontaneous polarization direction in the adjacent two domains can only be 90°or 180°. the interfaces of the corresponding domains, are referred to as 90°domain walls and 180° domain walls, respectively.
The movement of the domain under the action of an external electric field. If a sufficiently high DC electric field is applied to a multi-domain crystal, the domain of the spontaneous polarization direction and the direction of the electric field will continue to increase and vice versa. The entire crystal changes from multi-domain to single domain, and the direction of spontaneous polarization is consistent with the direction of the electric field. The polarization process of piezo ceramic bimorph is to add a sufficiently high DC electric field to the electrodes of the ceramic plates to force the domains to turn even if their spontaneous polarization is aligned. PS is the spontaneous polarization, Pr is the residual polarization, and EC is the coercive field strength. In the piezoelectric ceramic polarization process, an EC having an electric field strength of 2-3 times is generally selected. A further understanding of the piezoelectric effect is that the residual polarization in a polarized piezoelectric ceramic is always expressed in the form of an electric dipole moment, that is, a positively bound charge at one end of the piezo ceramic and a negatively bound charge at the other end, for shielding and to counteract the effect of the residual polarization on the outside world under the action of the bound charge, a free charge from the outside is adsorbed on the ceramic electrode surface.
The movement of the domain under the action of an external electric field. If a sufficiently high DC electric field is applied to a multi-domain crystal, the domain of the spontaneous polarization direction and the direction of the electric field will continue to increase and vice versa. The entire crystal changes from multi-domain to single domain and the direction of spontaneous polarization.which is consistent with the direction of the electric field. The polarization process of piezoelectric ceramics is to add a sufficiently high DC electric field to the electrodes of the piezo discs piezoceramic transducer to force the domains to turn even if their spontaneous polarization is aligned. PS is the spontaneous polarization, Pr is the residual polarization, and EC is the coercive field strength In the piezoelectric ceramic polarization process, an EC is having an electric field strength of 2-3 times is generally selected. A further understanding of the piezoelectric effect is that the residual polarization in a polarized piezoelectric ceramic is always expressed in the form of an electric dipole moment, that is, a positively bound charges at one end of the piezo ceramic and a negatively bound charge at the other end, for shielding and To counteract the effect of the residual polarization on the outside world under the action of the bound charge, a free charge from the outside is adsorbed on the ceramic electrode surface.
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