5 Things to Know Before Buying Crystal Piezoelectric Materials

Piezoelectric crystals have been promoted to a wide range of application fields. Face so many manufactures, how to successfully purchase the best piezo crystals at lower buying cost? Being a knowledgeable customer is the key. Here are several things to you should know.

What's the best piezoelectric crystals

Most of the piezo crystals on the market have their own formulation and performance standards, there's no exact definition of the best piezo crystal. Sometimes various parameter values tend to achieve a state of equilibrium, it means that excessive demand on one or two indices is purchased at the price of the other indices. As a manufacture, we often face a situation just like that, one client bought a type of piezo ceramics from us, after being used for some time, they found out that the sensitivity is too high and reach the saturation level which are unavailable for their applications. We tried to take a change of some crystals with lower properties which are marked as unqualified products in stock, It was amazing that the result was quite good.

Let's come to conclusion that we can't simply judge piezoelectric crystals as the worst or the best. As long as they reach a certain performance, the most suitable is the best. So the point is that we must make detailed investigations to both property of piezoelectric materials and demand of application before buying them.

Price factor in buying decision

Price is one of the most important factor for customers in buying piezo crystals. Generally, because the manufactures have high fixed costs but low variable costs, there is a strong relationship between buying quantity and price. So, as production increased, the manufacturing costs for each unit will be reduced. Even the prices for same products is variable in different batches of production.

As a buyer, especially in case of some small quantity purchases, if the demand is not strict, we should try to choose the piezo crystals which are approaching to our requirements in stock. Because compare to the high price of customized products, most of the stock are the rest of batch production at a very low-level cost, it will help us easily get the best price or discounts from manufactures.

The materials of piezoelectric crystals

Due to the wide range of possible shapes, Lead Zirconate Titanate(PZT) has become the most broadly used piezoceramic materials. PZT crystals are composed of two kinds of crystals, i.e. lead titanate (PbTiO3) and lead zirconate (PbZrO3). According to the difference of performance, they are often broken into three groups, PZT-4, PZT-5 and PZT-8. Different groups of materials have their respective areas of application. Knowing about this point is crytical for us to buy the best piezoelectric crystals.

PZT5 piezoelectric materials have charactor of high sensitivity and large displacements, mainly used in many kinds of piezo products such as pressure sensors, accelerometers, flow meters, level sensors, medical ultrasonic testing, microphones, etc.

PZT8 piezoelectric materials have high mechanical quality factor and stability but low piezoelectric response. This type piezo crystals can be used for high power or high temperature applications such as ultrasonic cleaning, ultrasonic welding, ultrasonic drilling, ultrasonic liquid processing, ultrasonic cutting, ultrasonic motors, etc.

Closing to PZT8, PZT4 piezoelectric materials have higher mechanical quality factor and electromechanical coupling factors, typical applications include: ultrasonic atomizers, ultrasonic cleaner, high frequency transducers, ultrasonic sonicators and many kinds of high-power sensors.

Other technical parameters of piezoelectric crystals

In addition to the materials of ceramic elements, we need to learn about some key performance indicators before buying:

1) Shape & Dimension: Including square, rectangular, disc, ring, tube, bar, cylinder, ball, hemisphere and other Irregular shapes, this is the most basic requirement.

2) Piezoelectric modes of vibration: Piezoelectric elements have exceedingly complex vibration modes such as radial mode, length mode, width mode, thickness mode, longitudinal length mode, thickness shear mode, torsional mode, etc.

3) Resonance frequency: The frequency at which the amplitude of the crystal vibration can reach its maximum. Frequency matching is significant for the final performance of piezo products.

4) Piezoelectric constant: As one of the most important index, piezo constant indicates the conversion ratio about the electrical energy converted into mechanical energy, or vice versa.

However, there are a number of other influence factors such as working temperature, limiting voltage, resonance impedance, static capacitance, displacement and so on. All these factors will determine whether you can buy the best piezoelectric crystals.

Last Updated on April 18, by You Ling

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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

First of all, we need to understand how the piezoelectric effect of piezoelectric ceramics is produced. What are the structural types of piezoelectric ceramics? Only after we understand this knowledge can we choose the appropriate piezoelectric ceramics.

1、What is the Piezoelectric Effect?

Some dielectric materials experience polarization when subjected to external forces in a certain direction, resulting in the appearance of positive and negative charges on the two opposite surfaces of the crystal. This phenomenon is known as the piezoelectric effect, which can be divided into positive piezoelectric effect and inverse piezoelectric effect. The positive piezoelectric effect refers to the effect of mechanical stress on the crystal, causing it to become a dielectric and charge its surface. Conversely, when an external electric field is applied to the crystal, it undergoes mechanical deformation, known as the inverse piezoelectric effect.

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.

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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.

If using piezoelectric ceramics is only for cost reasons, the feasibility of the solution is worth considering.

• Please analyze and design your application correctly, and use the force and displacement that piezoelectric ceramics can achieve.

Be sure to pay attention to the rationality of mechanical design. Only by adopting reasonable mechanical design can the performance of piezoelectric ceramics be fully utilized, including high reliability, repeatability, and long service life.

If innovative piezoelectric ceramic technology is adopted, but the old mechanical structure system is still used, then the system upgrade will often fail, so it is necessary to consider redesigning the external mechanical structure system.

• Piezoelectric ceramics cannot cover all applications in all fields 100%.

Piezoelectric ceramics are usually targeted at different applications, and their applicability may not be reflected in the parameter table. Therefore, when choosing alternative products, careful analysis should be made.

• The technical parameters of piezoelectric ceramics are tested under different testing conditions.

When operated in different ways, piezoelectric ceramics may exhibit different performances, and the performance of piezoelectric ceramics with different piezoelectric materials and processes varies greatly.

• The service life and reliability of piezoelectric ceramics depend on the parameters of piezoelectric ceramics and application conditions.

Therefore, it is impossible to evaluate all reliability in one testing environment. The method is to conduct system testing under a set of actual operating conditions. Even for well-running piezoelectric mechanical systems, new parameter calibration and applicability evaluation are required for small changes in driving conditions or system design.

Please note:

• 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!

6、Piezo Ceramic Manufacturer Recommendations

APC International Ltd. – Mackeyville, PA

• Custom Manufacturer

Boston Piezo-Optics Inc. – Bellingham, MA

• Custom Manufacturer

Columbia Research Laboratories Inc. – Woodlyn, PA

• Stock Manufacturer

Elent A / Elent Technics Ltd. – Dnipro, Ukraine

• Custom Manufacturer

Johnson Matthey Piezo Products GmbH – Redwitz, Germany

• Stock Manufacturer
• Custom Manufacturer
• Supplier/Distributor

Physik Instrumente (PI) GmbH & Co. KG – Karlsruhe, Germany

• Stock Manufacturer

PI Ceramic GmbH, Sub. of Physik Instrumente (PI) GmbH & Co. KG, Piezo Technology – Lederhose, Germany

• Stock Manufacturer
• Custom Manufacturer

Piezo Technologies, An Amphenol Co. – Indianapolis, IN

• Custom Manufacturer

Soitec – Bernin, France

• Custom Manufacturer

He-shuai,China

• Stock Manufacturer
• Custom Manufacturer
• Supplier/Distributor

7、The Future of Piezoelectric Ceramics

Piezoelectric technology, with its unique advantages, is increasingly being applied in the growing demand for energy today. Piezoelectric ceramics, as an important functional material, have excellent electrical properties such as piezoelectricity, dielectricity, and optoelectronics, and are widely used in high-tech fields such as electronics, aerospace, and biology. With the rapid development of emerging fields and new economic and social development needs, there will be higher demands for the performance of piezoelectric ceramics in the future. For example, high Curie temperature, high electromechanical coupling coefficient, mechanical quality factor, as well as environmentally friendly, lead-free, composite, and nanoscale piezoelectric ceramics will undoubtedly become the focus of future research.

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