Piezoelectric Ceramic Composition with Cu Electrodes
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Solution Overview
Problem
Conventional piezoelectric ceramic compositions using Cu as internal electrodes for laminated piezoelectric elements face degradation in piezoelectric properties due to oxygen vacancies generated during low-temperature sintering in reductive atmospheres, leading to impaired electric resistance and reliability issues.
Innovation Solution
A laminated piezoelectric element comprising a piezoelectric ceramic composition with a composite oxide formula (Pb a-b Me b ) [(Zn 1/3 Nb 2/3 ) x TiyZr z ] O 3, where 0.96 ≤ a ≤ 1.03, 0 ≤ b ≤ 0.1, 0.05 ≤ x ≤ 0.15, 0.25 ≤ y ≤ 0.5, 0.35 ≤ z ≤ 0.6, and Me being Sr, Ca, or Ba, with 0.01 to 1.0 wt.-% of Cu and 0.01 to 0.5 wt.-% of Ag, and Cu diffusing into the piezoelectric layers to inhibit electric resistance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-temperature sintering in reductive atmosphere is used with Cu internal electrodes, then cost is reduced and Cu can be used instead of noble metals, but oxygen vacancies are generated that degrade electric resistance and reliability
Solution Approach 1:
The patent converts the harmful effect of oxygen vacancies (which normally degrade electric resistance) into a beneficial effect by controlling their formation during reductive sintering. The Cu diffusion into piezoelectric layers, initially a potential harm, is transformed into a benefit that compensates for the resistance degradation caused by oxygen vacancies, thereby maintaining reliability while enabling low-cost Cu electrodes
Solution Approach 2:
The patent changes the chemical composition parameters of the piezoelectric ceramic by controlling Cu content (0.01-1.0 wt.%) and Ag content (0.01-0.5 wt.%) in the composite oxide, and adjusting sintering parameters (temperature 800-1200°C, oxygen partial pressure 1.013×10^-5 to 1.013×10^-10 atm) to achieve optimal balance between cost reduction and reliability maintenance
2Temperature
If low-temperature sintering is used, then manufacturing cost is reduced and Cu can be used for internal electrodes, but piezoelectric properties are degraded due to oxygen vacancies
Solution Approach 1:
The patent transforms the harmful oxygen vacancies generated during low-temperature reductive sintering into a manageable condition by using Cu diffusion to compensate for their negative effects on piezoelectric properties, thereby enabling low-temperature processing without sacrificing performance
Solution Approach 2:
The patent creates a composite structure where Cu diffuses into the piezoelectric ceramic matrix, forming a composite material system that combines the advantages of low-temperature sintering with maintained piezoelectric properties through the synergistic interaction between Cu and the ceramic matrix
3Ease of manufacture
If Cu is used as internal electrode material, then cost is reduced compared to noble metals, but oxidation occurs in oxidative atmosphere impairing conductivity
Solution Approach 1:
The patent employs a reductive atmosphere (low oxygen partial pressure) during sintering, which acts as a protective environment preventing Cu oxidation. This inert-like atmosphere allows Cu to maintain its conductivity while enabling cost-effective electrode material selection
Solution Approach 2:
The patent changes the atmospheric parameters (oxygen partial pressure) during sintering to create conditions where Cu remains conductive and resistant to oxidation, thereby enabling cost reduction without sacrificing electrical performance
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 solution maintains high piezoelectric properties and inhibits electric resistance degradation at high temperatures, enhancing the reliability and performance of laminated piezoelectric elements while allowing for low-cost Cu usage and low-temperature sintering.
Implementation Method 1
the Cu contained in the internal electrode layers has diffused into the piezoelectric layers
Data Source
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AI summary
For the purpose of preventing the degradation of the piezoelectric strain properties when Cu is used for internal electrodes, there is provided a piezoelectric ceramic composition including: a composite oxide, as a main constituent thereof, represented by (Pba-bMeb)[(Zn1/3Nb2/3)xTiyZrz]O3 with the proviso that 0.96 ≤ a ≤ 1.03, 0 ≤ b ≤ 0.1, 0.05 ≤ x ≤ 0.15, 0.25 ≤ y ≤ 0.5, 0.35 ≤ z ≤ 0.6, and x + y + z = 1, and Me represents at least one selected from Sr, Ca and Ba; and at least one selected from Co, Mg, Ni, Cr and Ga as a first additive to the main constituent in a content of 0.5% by mass or less (not inclusive of 0) in terms of oxide, wherein an electrode made of Cu is to be disposed on the piezoelectric ceramic composition.