1、 Why is it necessary to conduct electrical strain loop testing on functional ceramics?

Traditional structural ceramics (such as alumina and silicon nitride) are mainly used for load-bearing or thermal insulation, and usually do not have significant electrical mechanical coupling effects. However, functional ceramics, especially ferroelectric/piezoelectric ceramics (such as lead zirconate titanate PZT, barium titanate BaTiO3, etc.), can undergo reversible small deformations (i.e. strain) under external electric fields, which forms the basis for their wide application in modern smart devices, including ultrasonic transducers, drivers, sensors, and actuators.

In order to scientifically evaluate the deformation ability, response linearity, hysteresis behavior, and repeatability of such materials under electric field excitation, a systematic electric field strain response test needs to be conducted, and its output is the ElectromStrain Hysteresis Loop. This loop not only reflects the driving performance of the material, but also contains rich micro mechanism information.

2、 Definition and Physical Significance of Electromagnetically Induced Strain Loop Line

1. What is an electrostrictive loop?

The electrically induced strain loop refers to the closed curve formed by the periodic variation of strain (S) with the applied electric field (E). Typical features include:

Strain peaks appear in both positive and negative electric field regions;

Overall presenting a symmetrical or asymmetrical bimodal loop structure;

The phenomenon of "necking" appears in the loop, especially in relaxor ferroelectrics.

This loop intuitively reveals the entire electromechanical response process of materials under alternating electric fields, and is a key basis for evaluating their applicability as driving or sensing materials.

2. Analysis of Physical Mechanisms

The main sources of electrical strain are two types of physical effects:

Converge Piezoelectric Effect:

Exists in polarized ferroelectric ceramics. The electric field causes lattice distortion, resulting in approximately linear strain with directional dependence. The strain signs are opposite under positive and negative electric fields.

Electrostriction effect:

Widely present in all dielectric materials, particularly prominent in relaxor ferroelectrics. Strain is proportional to the square of the electric field, with no polarity dependence, and both positive and negative electric fields produce strain in the same direction.

Therefore:

Unpolarized or relaxed ceramics (such as PMN-PT): mainly based on electrostriction, with highly symmetrical loops;

Fully polarized piezoelectric ceramics (such as PZT): the inverse piezoelectric effect is combined with electrostriction, and the loop often exhibits an asymmetric shape.

3、 Testing method

1. Composition of the testing system

A complete electrical strain loop testing system includes the following modules:

High voltage signal source: an alternating electric field with a voltage of up to several thousand volts (commonly known as sine wave or triangular wave);

Displacement/strain sensor:

Laser vibrometer - non-contact, nanoscale resolution;

Electric field monitoring unit: Measure the applied voltage through a high-voltage probe and calculate the electric field strength (E=V/d) based on the sample thickness (d);

Synchronous data acquisition system: Real time recording of electric field and strain signals, generating S-E loops.

2. Sample preparation requirements

Geometric shape: usually circular to ensure uniform electric field and reduce the risk of breakdown;

Electrode preparation: Conductive electrodes need to be prepared on both sides, and common methods include silver paste sintering, magnetron sputtering of gold or platinum;

Polarization treatment: If the inverse piezoelectric effect needs to be studied, the sample must be polarized by applying a high DC electric field at high temperature and aged for more than 24 hours to stabilize its performance.

4、 Key parameters of electrostriction loop

Strain: The amount of deformation that a material can achieve under a given electric field directly determines its ability to drive displacement;

Residual strain: The residual strain after the electric field is reset, reflecting the degree of irreversible deformation or domain wall pinning;

Loop symmetry: symmetry → dominated by electrostriction; Asymmetric → with significant inverse piezoelectric contribution;

Pinching degree: The more pronounced the necking, the more obstructed the polarization reversal, which is commonly seen in relaxor ferroelectrics or multiphase coexisting systems;

Loop area: characterizes the size of loss and hysteresis. The larger the area, the lower the control accuracy.

5、 Application and Significance

Electrical strain loop testing in the fields of scientific research and engineering:

Material research and screening: quickly comparing the driving performance of different components;

Device modeling and design: Provide input (electric field) - output (strain) relationship models for drivers, micro displacement platforms, etc;

Microscopic mechanism research: analysis of ferroelectric domain flipping dynamics, phase transition behavior, etc. through loop evolution;

Reliability assessment: After millions of electric field cycles, observe loop degradation and predict device lifespan.

As a core means of characterizing the electromechanical coupling performance of ferroelectric/piezoelectric ceramics, the electrostriction loop test not only reveals the macroscopic response of the material under external field action, but also connects the microstructure and macroscopic function.

The ferroelectric testing system of Huace Instrument has the capability of high voltage driving, nanoscale displacement detection, and multi parameter synchronous analysis, which can complete the full cycle measurement of the electrostriction loop and provide solid support for the industrialization of functional ceramics from the laboratory.