Last Updated on May 19, 2023 by You Ling
The crystal structure and piezoelectric properties of piezoelectric ceramics are closely related. Currently, the most widely used piezoelectric ceramics are perovskite-structured ceramics. Tungsten bronze structure and bismuth layered structure ceramics are less commonly used.
Perovskite-structured ceramics are the most widely studied and applied, with the electrical properties of perovskite crystals being one of their main characteristics. Due to the presence of many ion vacancies, perovskite crystals have good ion conduction performance. Moreover, perovskite crystals have a large dielectric constant and piezoelectric effect, making them widely applicable in the electronics industry.
Tungsten bronze structure ceramics have low dielectric loss, high spontaneous polarization intensity, and high Curie temperature. However, the sintering temperature of tungsten bronze materials is relatively high, and their preparation is difficult. The poor temperature stability has resulted in limited applications of tungsten bronze structured piezoelectric materials.
Bismuth layered structure ceramics exhibit significant electrical anisotropy, 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. Therefore, these ceramics have a wide range of applications in filters, energy conversion, high temperature, and high-frequency fields. However, they are difficult to polarize and have lower piezoelectric activity.
What are the crystal structures and characteristics of piezoelectric ceramics?
The practical piezoelectric ceramic materials are mainly divided into:
(1) Perovskite structure
Ferroelectric and piezoelectric ceramics with perovskite structures belong to the ABO3 type of octahedra, where A represents monovalent or divalent metal ions, and B represents tetravalent or pentavalent metals. Examples of perovskite-structured ferroelectric piezoelectric ceramics include barium titanate, lead titanate, lead zirconate, and KxNa1-xNbO3.
(2) Tungsten bronze structure
Ferroelectric and piezoelectric ceramics with tungsten bronze structures also belong to the ABO3 type of octahedra. Examples include lead niobate and strontium barium niobate.
(3) Bismuth layer structure
Bismuth layered structures can be seen as alternating layers of perovskite-like layers and {Bi2O12} layers. The perovskite-like layers can be one layer (e.g., Bi2WO6), two layers (e.g., PbBi2Nb3O9), three layers (e.g., Bi4Ti8O12), or up to five layers.
(4) Pyrochlore structure
Pyrochlore structures are composed of common {NbO6 or TaO6} octahedra, and larger Cd2+{or Pb2+} ions are located in the gaps between the octahedra. Ferroelectrics of this structure are only found in a limited number of compounds, such as Cd2Nb2O2, Pb2Nb2O2, and Cd2Ta2O7.
Classification by main components:
(1) Unit system ceramics
Practical unit systems have crystal structures that are almost all represented by BaTiO3 perovskite structures and PbNbO6 calcium bronze structures.
- Barium titanate ceramics
Barium titanate ceramics are a type of ferroelectric ceramics with a typical perovskite structure.
- Lead titanate ceramics
Lead titanate ceramics are ferroelectric ceramics with a perovskite structure.
(2)Binary system ceramics
Binary system piezoelectric ceramics are solid solutions formed by two chemical compounds with the ABO3 structure, where A represents divalent positive ions like Pb2+, Ba2+, Mg2+, Ca2+, Sr2+, etc., or monovalent positive ions like K+, Na+, etc., and B represents tetravalent positive ions like Zr4+, Ti4+ or pentavalent ions like Nb5+. The most common binary system piezoelectric ceramics are PbZrxTi(1-x)O3. By adjusting the molar ratio of the two ABO3 structures and modifying them with replacement elements and additives, various materials for different purposes can be obtained.
Lead zirconate ceramics
PbZrxTi(1-x)O3 lead zirconate ceramics, commonly referred to as PZT ceramics, are widely used. They are solid solutions of PbZrO3 and PbTiO3 with a perovskite structure. When the zirconium-titanium ratio is around 53/47 (i.e., near the eutectic boundary), they exhibit the strongest piezoelectric performance.
(3) Ternary system ceramics
Ternary system ceramics are typically formed by adding a third compound (with the chemical formula ABO3) to the binary system of lead zirconate titanate (PbZrO3-PbTiO3) with a perovskite structure. The added third component shares the common feature of not altering the overall perovskite lattice structure when forming a solid solution with PbZrO3-PbTiO3.
2、Conclusion
In summary, piezoelectric ceramics can have various crystal structures, such as perovskite, tungsten bronze, bismuth layer, and pyrochlore structures, each with unique characteristics. By adjusting the composition of these structures and modifying them with replacement elements and additives, a wide range of piezoelectric materials with different properties and applications can be obtained.
