Lead-Free Piezoelectric Composition Stabilizing Iron Valence
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Solution Overview
Problem
Conventional lead-free piezoelectric compositions, such as binary and ternary compounds including barium titanate and bismuth ferrite, face challenges in achieving high piezoelectric constants (d33) and specific resistance, especially after poling processes, due to anisotropy, high leakage current, and volatilization of bismuth, which affects their performance and stability.
Innovation Solution
A piezoelectric composition represented by the formula x[BiFeO3]-y[BaTiO3]-z[BiAlO3], where 0.5≤x≤0.7995, 0.2≤y≤0.4, 0.0005≤z≤0.1, and x+y+z=1, is developed, incorporating aluminum (Al) to stabilize the valence of iron and reduce bismuth volatilization, thereby enhancing specific resistance and piezoelectric performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If bismuth ferrite (BFO) is used as a lead-free piezoelectric composition, then the curie temperature is high and spontaneous polarization is large, but the piezoelectric constant is insufficient due to high anisotropy and large leakage current
Solution Approach 1:
The patent creates a composite piezoelectric material by combining bismuth ferrite (BFO) with barium titanate (BT) and bismuth aluminate (BA) in specific ratios. This composite approach allows the material to inherit the high curie temperature from BFO while the BT and BA components reduce anisotropy and leakage current, thereby achieving both high temperature stability and sufficient piezoelectric constant.
Solution Approach 2:
The patent systematically varies the compositional parameters (x, y, z ratios of BFO, BT, and BA) to optimize performance. By adjusting these parameters within specific ranges, the material achieves the desired balance between high curie temperature and adequate piezoelectric constant, demonstrating parameter optimization to resolve the contradiction.
2Object-affected harmful factors
If barium titanate and bismuth ferrite binary compound is used, then the piezoelectric composition does not contain lead, but the piezoelectric constant after poling is only around 130 pC/N which is small
Solution Approach 1:
The patent extends the binary BFO-BT system to a ternary composite by adding bismuth aluminate (BA). This additional component specifically addresses the insufficient piezoelectric constant issue while maintaining the lead-free characteristic. The BA phase helps reduce anisotropy and improve domain wall mobility, enabling higher piezoelectric constants in the poled state.
Solution Approach 2:
The patent introduces localized phases with different properties into the composite. The BFO phase provides high curie temperature, the BT phase contributes to piezoelectric response, and the BA phase specifically targets reducing anisotropy. This local quality differentiation allows each component to address specific performance limitations.
3Object-affected harmful factors
If ternary compound with bismuth magnesate titanate is used, then the composition is lead-free, but the material is greatly distorted under high electric field and cannot achieve large piezoelectric constant after poling
Solution Approach 1:
The patent replaces bismuth magnesate titanate with a BFO-BT-BA composite system. The BA component specifically addresses the distortion issue under high electric fields by stabilizing the crystal structure and reducing anisotropy, while maintaining lead-free composition. This composite approach achieves both mechanical stability and adequate piezoelectric constant.
Solution Approach 2:
The patent optimizes the compositional parameters to achieve the right balance between softness (for piezoelectric response) and structural stability (for resistance to distortion). By carefully controlling the ratios of BFO, BT, and BA within specific ranges, the material achieves sufficient resistance to distortion under high electric fields while maintaining adequate piezoelectric constant after poling.
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 composition achieves a large d33 and high specific resistance, reducing leakage current and improving polarization reversal, resulting in enhanced piezoelectric characteristics and stability, making it suitable for various applications like radiators and sensors.
Implementation Method 1
A perovskite-type metal oxide is known as a common piezoelectric composition... lead zirconate titanate (Pb(Zr, Ti)O3)... bismuth ferrite (BiFeO3)
Implementation Method 2
bismuth ferrite (BFO)... exhibits large spontaneous polarization... after a poling process is performed thereon
Data Source
AI summary
The piezoelectric composition is represented by the following Chemical Formula (1):x[BimFeO3]-y[BamTiO3]-z[BimAlO3] (1)wherein 0.5≤x≤0.7995, 0.2≤y≤0.4, 0.0005≤z≤0.1, x+y+z=1, 0.96≤m≤1.04.