Lead-Free Piezoelectric Ceramics with Compositional Gradients
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Solution Overview
Problem
Lead-containing piezoelectric materials, such as PZT, pose environmental concerns due to lead leaching, and existing lead-free alternatives like barium titanate exhibit unstable piezoelectric constants with temperature fluctuations, making precise control of piezoelectric devices difficult.
Innovation Solution
A lead-free piezoelectric ceramics with a perovskite-type metal oxide composition of ABO3, where A site elements include Ba and Ca or Bi, and B site elements include Ti and Zr or Hf, with controlled concentration gradients to stabilize the piezoelectric constant across a practical temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free perovskite-type oxide (barium titanate) is used as piezoelectric ceramics, then environmental impact is reduced, but piezoelectric constant fluctuates significantly with temperature changes
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of M2 elements (Zr, Sn, or Hf) within the piezoelectric ceramics structure. The B site element composition varies spatially, with different regions having different M2 concentrations to compensate for temperature-induced piezoelectric constant fluctuations. This local compositional variation allows the material to maintain stable piezoelectric properties across a wide temperature range while remaining lead-free.
Solution Approach 2:
The patent uses composite materials by combining multiple elements (Ba, M1, T1, M2, and O) to form a complex perovskite-type oxide with formula (Ba, M1)(T1, M2)O3. The composite structure incorporates M1 elements (Ca, Bi, or Sr) at the A site and M2 elements (Zr, Sn, or Hf) at the B site, creating a multi-element system that achieves both environmental friendliness and temperature-stable piezoelectric performance.
2Reliability
If piezoelectric constant is increased by increasing average grain diameter to 60.9 μm, then piezoelectric property improves, but fine processability and mechanical strength are lowered
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration of M2 elements (Zr, Sn, or Hf) at the B site within specific ranges (0.01 ≤ m ≤ 0.06). By precisely controlling this compositional parameter, the invention achieves high piezoelectric constants without requiring excessive grain growth, thereby maintaining fine processability. The parameter optimization allows achieving d33 ≥ 150 pC/N with manageable grain sizes suitable for practical manufacturing.
3Reliability
If piezoelectric constant is increased by increasing average grain diameter, then piezoelectric property improves, but mechanical strength is lowered
Solution Approach 1:
The patent uses parameter changes by controlling the M2 element concentration within optimal ranges to achieve high piezoelectric constants without excessive grain growth. The compositional optimization (0.01 ≤ m ≤ 0.06 for M2 content) enables achieving d33 ≥ 150 pC/N while maintaining grain sizes that preserve mechanical strength, avoiding the need for extremely large grains (60.9 μm) that would compromise structural integrity.
Solution Approach 2:
The patent employs composite materials by incorporating M2 elements (Zr, Sn, or Hf) into the perovskite structure, creating a multi-element system that simultaneously enhances piezoelectric properties and maintains mechanical strength. The composite composition (Ba, M1)(T1, M2)O3 provides both high piezoelectric constant and adequate mechanical properties through synergistic element interactions, eliminating the need for extreme grain growth.
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 provides a stable piezoelectric constant in the range of 0°C to 40°C, reducing temperature-dependent fluctuations and minimizing environmental impact by eliminating lead, thus enabling precise control of piezoelectric devices.
Implementation Method 1
A piezoelectric element obtained by forming electrodes on a surface of a piezoelectric material is used in a variety of piezoelectric devices and electronic devices, such as an actuator, an oscillator, a sensor, and a filter, by utilizing its piezoelectric effect.
Data Source
AI summary
Provided is a piezoelectric ceramics having a gradual change in piezoelectric constant depending on an ambient temperature. Specifically, provided is a single-piece piezoelectric ceramics including as a main component a perovskite-type metal oxide represented by a compositional formula of ABO3, wherein an A site element in the compositional formula contains Ba and M1, the M1 being formed of at least one kind selected from the group consisting of Ca and Bi, wherein a B site element in the compositional formula contains T1 and M2, the M2 being formed of at least one kind selected from the group consisting of Zr, Sn, and Hf, wherein concentrations of the M1 and the M2 change in at least one direction of the piezoelectric ceramics, and wherein increase and decrease directions of concentration changes of the M1 and the M2 are directions opposite to each other.