Core-Shell Piezoelectric Composition for Lead-Free High Performance
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Solution Overview
Problem
Existing piezoelectric compositions, such as those based on bismuth ferrite, face challenges in achieving high piezoelectric constants (d33) and Curie temperatures (Tc) while maintaining environmental and human safety due to lead content issues and anisotropy problems.
Innovation Solution
A piezoelectric composition comprising crystal particles with a core-shell structure, where the core and shell have different bismuth content ratios, optimizing the area ratio to achieve high d33 and Tc values, and a sintered body with a specific chemical composition of bismuth, iron, barium, and titanium, enhancing polarization reversal and dielectric properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead zirconate titanate (PZT) is used to achieve high piezoelectric constant and high Curie temperature, then piezoelectric performance is improved, but environmental and human safety deteriorates due to lead content
Solution Approach 1:
The patent changes the chemical composition parameters by replacing lead (Pb) with bismuth (Bi) in the perovskite structure, transitioning from Pb(Zr,Ti)O3 to Bi-containing piezoelectric compositions. This parameter change maintains the ABO3 perovskite structure while eliminating toxic lead, thereby preserving piezoelectric performance through structural similarity while improving environmental safety
Solution Approach 2:
The patent employs composite material strategies by combining bismuth ferrite (BFO) with other oxides such as barium titanate (BaTiO3) and bismuth magnesate titanate (BMT) to create composite piezoelectric compositions. These composites leverage the high Curie temperature of BFO while incorporating materials that reduce anisotropy and leakage current, achieving both high performance and lead-free composition
2Temperature
If bismuth ferrite (BFO) is used to achieve high Curie temperature and large spontaneous polarization, then thermal stability is improved, but piezoelectric constant deteriorates due to high anisotropy and large leakage current
Solution Approach 1:
The patent applies local quality modification by creating core-shell structured particles where the core contains bismuth ferrite for high Curie temperature and the shell contains other materials (such as barium titanate or bismuth magnesate titanate) that reduce anisotropy and leakage current. This local differentiation allows each region to contribute its advantageous properties to the overall composite
Solution Approach 2:
The patent creates composite materials by combining bismuth ferrite with barium titanate and/or bismuth magnesate titanate in specific ratios. The BFO phase provides high Curie temperature while the complementary phases reduce anisotropy and leakage current, achieving synergistic effects that improve piezoelectric constant while maintaining thermal stability
3Reliability
If core-shell structure with specific bismuth content ratio is implemented to optimize piezoelectric performance, then piezoelectric constant and Curie temperature are improved, but manufacturing complexity increases
Solution Approach 1:
The patent segments the piezoelectric particles into core and shell regions with different bismuth contents and material compositions. The core contains primarily bismuth ferrite for high Curie temperature, while the shell contains materials with lower bismuth content to reduce anisotropy. This segmentation allows independent optimization of each region's properties while maintaining overall compositional control
Solution Approach 2:
The patent controls the bismuth content parameter differently in core and shell regions, with the shell having lower bismuth content than the core. By adjusting this compositional parameter gradient and controlling the area ratio of core to shell cross-sections (100·SCORE/(SCORE+SSHELL) = 50 to 90), the patent optimizes both piezoelectric constant and Curie temperature while managing manufacturing complexity through parameter control
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 piezoelectric constant d33 of 200 pC/N or more and a Curie temperature Tc of 250°C or higher, improving piezoelectric performance and compatibility, while being lead-free and environmentally safer.
Implementation Method 1
a piezoelectric composition comprising a plurality of crystal particles, wherein the piezoelectric composition includes bismuth, iron, barium, titanium and oxygen
Implementation Method 2
the crystal particle includes a core and a shell having a content of bismuth higher than that in the core and covering the core
Data Source
AI summary
A piezoelectric composition comprises a plurality of crystal particles, wherein the piezoelectric composition includes bismuth, iron, barium, titanium, and oxygen; the crystal particle include a core and a shell having a contents of bismuth higher than that in the core and covering the core; and the total area of the cross sections of the cores exposed to the cross section of the piezoelectric composition is expressed as SCORE, the total area of the cross sections of the shells exposed to the cross section of the piezoelectric composition is expressed as SSHELL, and 100·SCORE/(SCORE+SSHELL) is 50 to 90.