Piezoelectric Ceramic with Localized Crystallinity for Hysteresis Control
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Solution Overview
Problem
Piezoelectric ceramics with bismuth layered compounds face issues with high hysteresis in charge output when loads are applied, leading to accuracy degradation in pressure detection, especially in high-temperature environments like engine cylinders.
Innovation Solution
A piezoelectric ceramic with a layered compound composition of Bi4Ti3O12·αMTiO3, where M is Sr or Ba and α is between 0.1 and 1, featuring a structure with a higher crystallinity outer region and a less crystalline inner region, reducing hysteresis by suppressing deformation in directions perpendicular to the applied load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a piezoelectric ceramic containing a bismuth layered compound as a main component is used, then the Curie temperature is increased to about 400°C or higher, but the hysteresis of the charge output becomes relatively large
Solution Approach 1:
The invention creates a composite structure with an outer region having high crystallinity and an inner region having lower crystallinity. This local differentiation of crystal structure quality allows the outer region to suppress deformation while the inner region maintains piezoelectric activity, resolving the contradiction between high Curie temperature and low hysteresis.
Solution Approach 2:
The invention combines two regions with different crystallinity levels within a single piezoelectric ceramic body. The outer region with high crystallinity provides structural stability and low hysteresis, while the inner region with lower crystallinity maintains the piezoelectric properties necessary for charge output, achieving both high Curie temperature and low hysteresis through composite structure.
2Measurement precision
If a PZT-based material or PT-based material is used, then the piezoelectric constant d is large, but the Curie temperature is only about 200 to 300°C and the heat resistance is insufficient
Solution Approach 1:
The invention uses a bismuth layered compound as the main component which inherently provides a high Curie temperature of about 400°C or higher. By creating a composite structure with differentiated crystallinity, the invention maintains both the high piezoelectric constant and the high heat resistance, overcoming the limitations of conventional PZT or PT materials.
Solution Approach 2:
The invention changes the crystallinity parameter spatially within the ceramic body, creating regions with different degrees of crystallinity. This parameter change allows the material to simultaneously exhibit high piezoelectric constant characteristics and high heat resistance, resolving the contradiction between measurement precision and temperature tolerance.
3Temperature
If a piezoelectric sensor is exposed to high temperatures during combustion, then the temperature reaches 150°C or higher, but the piezoelectric constant d significantly changes making accurate pressure detection difficult
Solution Approach 1:
The invention creates a composite structure with an outer region having high crystallinity and an inner region having lower crystallinity. This local differentiation provides thermal stability while maintaining piezoelectric sensitivity, allowing accurate pressure detection at high operating temperatures of 150°C or higher.
Solution Approach 2:
By combining regions with different crystallinity levels, the invention creates a material that is both thermally stable and piezoelectrically active. The outer high-crystallinity region provides thermal stability for high-temperature operation, while the inner region maintains the piezoelectric constant necessary for accurate pressure detection.
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 ceramic achieves reduced hysteresis and improved heat resistance, enabling accurate pressure detection over a wide temperature range with minimal energy loss, enhancing the reliability of piezoelectric sensors.
Implementation Method 1
The piezoelectric sensor is connected to the pressure transmission pin, receives the pressure in the cylinder through the pressure transmission pin, and outputs a charge (an output charge) corresponding to the pressure.
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
[Object] A piezoelectric ceramic which has small hysteresis in an output charge output from the piezoelectric ceramic when a load is applied. [Solution] A piezoelectric ceramic 20 includes a pair of main surfaces 2a and 2b that are on opposing sides of a base body 21 and parallel to each other and a side surface 4 continuous to edges 3a and 3b of the pair of main surfaces 2a and 2b. The piezoelectric ceramic contains a layered compound that has a composition formula Bi4Ti3O12·αMTiO3 where M is at least one selected from Sr and Ba and α satisfies 0.1 ≤ α ≤ 1, as a main component. The base body 21 includes an outer region 22 that includes the side surface 4 and adjacent regions 4A and 4B of the pair of main surfaces 2a and 2b and an inner region 24 surrounded by the outer region 22. A full width half maximum WA of a peak in a range where a diffraction angle (2θ) is 22.8° to 23.5° in an X-ray diffraction pattern using a Cu-Kα ray on the side surface 4 of the outer region 22 is smaller than a full width half maximum WB of a peak in the range where a diffraction angle (2θ) is 22.8° to 23.5° in the X-ray diffraction pattern using the Cu-Kα ray on the main surfaces 2a and 2b of the inner region 24.