Composite Piezoelectric Ceramic Heterojunction for High-Temperature Stability
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Solution Overview
Problem
Lead-containing piezoelectric ceramic materials, such as PZT, pose environmental concerns due to lead elution, and Pb-free alternatives like BaTiO3 and KNbO3-based ceramics have limited temperature stability and piezoelectric performance, restricting their use to temperatures below 100°C and displacements.
Innovation Solution
A composite piezoelectric ceramic with a solid solution of KNbO3 and NaNbO3, coated with a thin BaTiO3 layer forming a heterojunction, enhances the Curie temperature and piezoelectric characteristics, allowing operation above 100°C and low-temperature sintering at 300°C or below, while minimizing lead content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Pb-free piezoelectric ceramic materials like BaTiO3 and KNbO3 are used to replace PZT, then environmental harm is reduced, but piezoelectric characteristics and displacement capability deteriorate
Solution Approach 1:
The patent creates a composite piezoelectric ceramic combining KNbO3-based solid solution and BaTiO3 in a specific molar ratio (0.3-0.7:0.7-0.3). This composite structure leverages the complementary properties of both materials to achieve sufficient piezoelectric characteristics while maintaining Pb-free composition, directly resolving the contradiction between environmental safety and functional performance.
Solution Approach 2:
The patent optimizes the molar ratio parameters of KNbO3 and BaTiO3 components, along with sintering temperature and atmosphere parameters, to achieve the desired balance between environmental compatibility and piezoelectric performance. By carefully controlling these parameters, the material achieves adequate displacement capability without lead content.
2Temperature
If BaTiO3-based piezoelectric ceramics are used, then Curie temperature is limited to about 120°C, but this limits service temperature to 100°C or below
Solution Approach 1:
The patent modifies the composition parameters by creating a solid solution of KNbO3 and BaTiO3 in controlled molar ratios, which elevates the Curie temperature from BaTiO3's 120°C to above 100°C. This parameter change enables the material to maintain piezoelectric characteristics at higher service temperatures, expanding the adaptable temperature range for practical applications.
3Reliability
If KNbO3/BaTiO3 binary solid solution is used, then piezoelectric characteristics may be improved, but sintering temperature range becomes very narrow
Solution Approach 1:
The patent introduces NaNbO3 as a third component to modify the sintering behavior of the KNbO3-BaTiO3 system. This compositional parameter change broadens the sintering temperature window, making the manufacturing process more robust and less sensitive to temperature variations while preserving the piezoelectric characteristics provided by the morphotropic phase boundary.
4Reliability
If excessively high sintering temperature is used for KNbO3/BaTiO3 binary system, then piezoelectric characteristics may be achieved, but composition variations occur due to element evaporation
Solution Approach 1:
The patent optimizes the sintering temperature parameter to a moderate range that is sufficient to achieve piezoelectric characteristics without causing excessive element evaporation. Additionally, the inclusion of NaNbO3 stabilizes the composition during sintering, reducing potassium loss and maintaining stoichiometric balance, thereby ensuring composition uniformity throughout the ceramic body.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composite ceramic exhibits improved piezoelectric performance and temperature stability, enabling effective displacement at elevated temperatures and reducing lead usage, thus addressing the limitations of Pb-free materials.
Implementation Method 1
Piezoelectric ceramics produce a mechanical strain and a stress in response to the application of an electric field
Implementation Method 2
A piezoelectric ceramic that is a solid solution of plural components is generally known to exhibit high piezoelectric characteristics due to the presence of a morphotropic phase boundary (MPB), for example, a tetragonal/orthorhombic phase boundary
Implementation Method 3
the KNbO3/BaTiO3 binary system has a very narrow range of temperatures at which it can be sintered
Data Source
AI summary
A composite piezoelectric ceramic includes a compact of crystal particles including at least one of potassium niobate (KNbO3) and sodium niobate (NaNbO3) and optionally further including lithium niobate (LiNbO3), and a layer containing barium titanate (BaTiO3) that is disposed on the surface of the compact while forming a heterojunction with the compact. A piezoelectric device includes the composite piezoelectric ceramic.