Lead-Free Piezoelectric Ceramic Composition for Thermal Stress Control
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Solution Overview
Problem
Existing lead-free piezoelectric ceramic compositions, such as potassium sodium niobate-based materials, face challenges in maintaining stable piezoelectric properties and reducing thermal stress due to significant changes in the coefficient of linear expansion during phase transitions between orthorhombic and tetragonal crystal structures within a specific temperature range.
Innovation Solution
A piezoelectric ceramic composition is formulated with a specific molar ratio of potassium, sodium, and lithium at the A-site, and niobium, tantalum, and antimony at the B-site, with controlled additions of silver, iron, and other metals, ensuring a transition temperature between crystal structures within a manageable range and a ratio of αt/αo greater than 0.72, thereby stabilizing the linear expansion coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free piezoelectric ceramic compositions are used, then environmental compatibility is improved, but piezoelectric properties stability deteriorates
Solution Approach 1:
The patent adjusts the molar ratios of K, Na, and Li at the A-site and Nb, Ta, and Sb at the B-site to optimize piezoelectric properties. Specifically, it controls the ratio of (K+Na+Li)/(Nb+Ta+Sb) and adjusts individual element ratios to achieve stable piezoelectric performance without lead. The patent also controls the ratio of αt/αo (thermal expansion coefficients) to be 0.72 or more, which stabilizes thermal stress and improves reliability.
Solution Approach 2:
The patent creates a composite piezoelectric ceramic system by combining multiple elements (K, Na, Li, Nb, Ta, Sb) in specific ratios. This multi-element composition allows the material to achieve both environmental compatibility (lead-free) and stable piezoelectric properties through synergistic effects of different elements, particularly by forming a perovskite structure with optimized A-site and B-site element combinations.
2Reliability
If phase transition between orthorhombic and tetragonal crystal structures occurs, then piezoelectric response is improved, but thermal stress increases
Solution Approach 1:
The patent controls the transition temperature between orthorhombic and tetragonal crystal structures to occur within a specific range (−20°C or higher and 60°C or lower). It also controls the ratio of thermal expansion coefficients αt/αo to be 0.72 or more, which minimizes the difference in linear expansion between the two crystal phases. This parameter optimization allows the material to exhibit strong piezoelectric response through phase transition while reducing thermal stress that would otherwise cause cracking or degradation.
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 improved piezoelectric properties and reduces thermal stress by minimizing the difference in linear expansion coefficients, stabilizing the operation of devices using the ceramic, particularly in environments where temperature fluctuations occur.
Implementation Method 1
piezoelectric ceramic composition and piezoelectric actuator
Implementation Method 2
a transition temperature at which a phase transition between an orthorhombic crystal structure and a tetragonal crystal structure occurs
Data Source
AI summary
In a piezoelectric ceramic composition including potassium sodium niobate, a transition temperature at which a phase transition between an orthorhombic crystal structure and a tetragonal crystal structure occurs lies in a temperature range of −20° C. or higher and 60° C. or lower. In the piezoelectric ceramic composition, αt/αo is 0.72 or more, where αo represents a coefficient of linear expansion determined when a crystal structure is orthorhombic in the temperature range, and αt represents a coefficient of linear expansion determined when a crystal structure is tetragonal in the temperature range.