Lead-Free Piezoelectric Composition with High Depolarization Temperature
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Solution Overview
Problem
Current lead-free piezoelectric compositions, such as bismuth ferrite, suffer from low piezoelectric constants and are prone to depolarization at high temperatures, making them unsuitable for practical use in piezoelectric devices.
Innovation Solution
A piezoelectric composition comprising a perovskite structure with a specific ratio of bismuth, barium, iron, and titanium, which exhibits a large piezoelectric constant and high depolarization temperature, achieved through a polarization treatment and sintering process that includes a two-step heating method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If bismuth ferrite is used as a lead-free piezoelectric composition, then the piezoelectric composition contains no lead, but the piezoelectric constant is insufficient due to high anisotropy and large leak current
Solution Approach 1:
The invention uses a composite material system comprising bismuth ferrite and barium titanate in a specific composition ratio (0.4 ≤ x ≤ 0.6 in formula xBiFeO3-(1-x)BaTiO3). This composite approach combines the lead-free advantage of BFO with the piezoelectric properties of BTO, achieving both environmental compliance and sufficient piezoelectric performance with d33 ≥ 100 pC/N
Solution Approach 2:
The invention optimizes the compositional parameter x in the formula xBiFeO3-(1-x)BaTiO3 within the range 0.4 ≤ x ≤ 0.6, and controls the ratio of diffraction peak intensities (IH/IL ≤ 2.00) to achieve optimal piezoelectric properties. This parameter optimization resolves the contradiction by finding the precise composition where lead-free and high piezoelectric constant requirements meet
2Reliability
If ternary compound (xBaTiO3-yBiFeO3-yBi(Mg0.5Ti0.5)O3) is used, then the piezoelectric constant is improved, but the composition becomes more complex
Solution Approach 1:
The invention extracts and eliminates the complex Bi(Mg0.5Ti0.5)O3 component from the ternary system, retaining only the essential BFO-BTO binary system. This simplification maintains adequate piezoelectric performance while significantly reducing compositional complexity and making the material system more practical for manufacturing
3Reliability
If binary compound (Ba1-yBiy)a(Ti1-x-zZrxFez)O3 is used, then the piezoelectric constant is large, but the Curie temperature and depolarization temperature are very low
Solution Approach 1:
The invention changes the compositional parameters to 0.4 ≤ x ≤ 0.6 in the formula xBiFeO3-(1-x)BaTiO3 and controls the diffraction peak intensity ratio IH/IL ≤ 2.00. This parameter optimization simultaneously achieves high piezoelectric constant (d33 ≥ 100 pC/N) and adequate depolarization temperature for practical applications
Solution Approach 2:
The composite BFO-BTO system with optimized composition ratios provides a balance between piezoelectric performance and thermal stability, resolving the contradiction between high piezoelectric constant and sufficient depolarization temperature
4Reliability
If piezoelectric composition is subjected to polarization treatment, then the piezoelectric properties are enhanced, but the composition is largely strained
Solution Approach 1:
The optimized compositional parameters (0.4 ≤ x ≤ 0.6) and crystal structure control (IH/IL ≤ 2.00) in the BFO-BTO system reduce internal stresses and improve mechanical tolerance, allowing the material to withstand polarization treatment without excessive strain while maintaining enhanced piezoelectric properties
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 significantly large piezoelectric constant (d33) and high depolarization temperature, ensuring stability and effectiveness in piezoelectric devices despite high temperatures, such as those encountered during soldering.
Implementation Method 1
Bismuth ferrite (BFO) presents with a large spontaneous polarization... piezoelectric composition having a large piezoelectric constant
Implementation Method 2
An X-ray diffraction pattern of the piezoelectric composition after a polarization treatment has a first peak and a second peak in the range of the diffraction angle 2θ of 38.6° or more and 39.6° or less
Data Source
AI summary
A piezoelectric composition comprises an oxide having a perovskite structure, wherein the oxide contains bismuth, barium, iron and titanium; the X-ray diffraction pattern of the piezoelectric composition after a polarization treatment has a first peak and a second peak in the range of the diffraction angle 2θ of 38.6° or more and 39.6° or less; the diffraction angle 2θ of the first peak is smaller than the diffraction angle 2θ of the second peak; an intensity of the first peak is represented as IL; an intensity of the second peak is represented as IH; and IH/IL is 0.00 or more and 2.00 or less.