Piezoelectric ceramics are complex electronic materials that exhibit different performance characteristics depending on the environment and mechanical design.
Therefore, reading the following article will help you easily determine which piezoelectric ceramic is suitable for your project.- What is the Piezoelectric Effect?
- How to Achieve the Piezoelectric Effect？
- Classification of Piezoelectric Ceramics by Structure
- How are piezoelectric ceramics made?
- How to choose the right piezoelectric ceramic?
- Piezo Ceramic Manufacturer Recommendations
- The Future of Piezoelectric Ceramics
2、How to Achieve the Piezoelectric Effect?
Piezoelectric ceramics require two conditions: first, the grains must exhibit ferroelectricity; second, they must undergo strong direct current (DC) polarization treatment. All ferroelectric single crystals exhibit piezoelectric effect, but in the case of ferroelectric ceramics (which are polycrystalline), they need to undergo high-voltage DC polarization treatment. This is because although the individual grains in ceramics exhibit spontaneous polarization and have ferroelectric properties, the orientation of their spontaneous polarization domains is entirely random and lacks macroscopic polarization strength. Under the action of high-voltage DC electric fields, the polarization domains align themselves in the direction of the electric field, and this oriented state can be largely retained after the electric field is removed, resulting in the manifestation of the piezoelectric effect in ceramics.
3、Classification of Piezoelectric Ceramics by Structure
Currently, piezoelectric ceramics can be mainly divided into three categories based on their structures: tungsten bronze structure, bismuth layer structure, and perovskite structure.
Tungsten Bronze Structure Ceramics:
Tungsten bronze structure is the second largest ferroelectric crystal structure after perovskite structure. The crystal is also formed by connecting octahedrons through shared vertices. The octahedrons are stacked along four-fold axes in a shared vertex manner, and the stacks are further connected in the same way. The widely studied systems in this category include (SrxBa1-x)Nb2O6, (AxSr1-x)NaNb5O15 (A = Ba, Ca, Mg, etc.), and Ba2AgNb5O15.
Features: This type of ceramic has a high spontaneous polarization strength, a relatively high Curie temperature (around 300℃), and a low dielectric loss. However, it has a high sintering temperature, is difficult to prepare, and has poor temperature stability.
Bismuth Layer Structure Ceramics:
Bismuth layer structure ceramics are ferroelectric compounds with a layered structure containing Bi and octahedrons. The widely studied systems in this category include Bi4Ti3O12, SrBi4Ti4O15, SrBi2Nb2O9, and their modified compounds.
Features: This type of ceramic exhibits significant anisotropic electrical properties, high mechanical quality factor, high Curie temperature, low relative dielectric constant, high resistivity, high dielectric breakdown strength, and good time and temperature stability of resonance frequency. However, its coercive field is relatively high, making it difficult to polarize and resulting in low piezoelectric activity.
Perovskite Structure Ceramics:
The most widely studied crystal structure currently is the perovskite structure. The chemical formula of this structure can be written as AB03, where A is a monovalent or divalent metal ion, and B is a tetravalent or pentavalent metal ion. The larger A cation, smaller B cation, and oxygen ion are located at the corner, body center, and face center of the unit cell, respectively. The commonly studied materials in this category include barium titanate, lead titanate, lead zirconate titanate, and KxNa1-xNbO3, among others.
4、Production Process of Piezoelectric CeramicsHow are piezoelectric ceramics made?
Production Process of Piezoelectric Ceramics
4.1 Preparation of Green Body
The green body is prepared by dry pressing. Prior to dry pressing, the powder must be granulated by adding a binder that accounts for about 5% of the material, stirring it evenly, and sieving it. Then, the pre-pressed block is crushed and sifted into a fine powder. The purpose of granulation is not only to distribute the binder more evenly in the powder, but also to compress the particles and expel any trapped air, making it easier to shape and resulting in a more uniform density in the molded samples.
4.2 Sintering and Machining of Ceramic Components
After dry pressing, the green body needs to be sintered at high temperature to become a ceramic component. Sintering is the process of particle rearrangement and densification as well as crystal growth. Excessive sintering temperature can cause the ceramic crystals to grow too large or the microstructure to be uneven, while a temperature that is too low can result in incomplete crystal development, both of which can affect the piezoelectric performance of the PZT ceramic component.
4.3 Electrode Deposition
Metal electrodes are necessary between the two layers of the PZT piezoelectric ceramic element to conduct electricity and exhibit piezoelectric properties. There are many traditional methods for depositing electrodes, such as silver burn-in, vacuum evaporation, chemical silver plating, and chemical copper plating.
4.4 Polarization
After the metal electrode is deposited onto the PZT piezoelectric ceramic element, it needs to be polarized to exhibit the piezoelectric effect. To achieve perfect polarization and fully realize its piezoelectric performance, the polarization conditions, including the polarization electric field, polarization temperature, and polarization time, must be reasonably selected. Only under the action of the polarization electric field can the electric domains be oriented and arranged along the electric field direction. The higher the polarization electric field, the greater the effect of promoting the orientation of the electric domains, and the more perfect the polarization will be.
5、How to choose the right piezoelectric ceramic?
Engineers from he-shuai company gave some suggestions:
Principles of using piezoelectric ceramics:
- Please make sure that piezoelectric ceramics will bring you advantages that other solutions cannot compare with in your application.
- Please analyze and design your application correctly, and use the force and displacement that piezoelectric ceramics can achieve.
- Piezoelectric ceramics cannot cover all applications in all fields 100%.
- The technical parameters of piezoelectric ceramics are tested under different testing conditions.
- The service life and reliability of piezoelectric ceramics depend on the parameters of piezoelectric ceramics and application conditions.
- Maximum displacement and maximum output cannot occur at the same time.
- The actual operating frequency of piezoelectric mechanical systems is usually much lower than the resonance frequency of piezoelectric ceramics!
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