The piezoelectric effect in ferroelectrics

In summary, the conversation is discussing the reason behind the appearance of voltage when mechanical stress is applied to a ferroelectric material like BaTiO3 Perovskite. The conversation mentions that below the Curie temperature, the structure of the material changes and there is an increase in polarization in each unit cell. The two main points of discussion are whether the movement of 90° domains contributes to the large strain observed in piezo ferroelectrics and whether this movement also contributes to the voltage when mechanical stress is applied. The central issue is whether the movement of domains itself leads to a higher polarization or if it is a condition for a higher polarization due to further stretching of the c-site. The main question is what is the exact reason
  • #1
qwerasadf
6
0
Hey,
I am confused, what is the exact reason for the appearance of a voltage upon a mechanical stress at a ferroelectric material like a BaTiO3 Perovskite?
Below the Curie temperature the structure is no more cubic but tetragonal, let's say c-site is now longer than a- and b-site. And of course there is a polarization in each unit cell now. Ok, now we do mechanical stress at the material. I assume there are many contribution for the resulting increase of net polarization:

First, we do the same as we do at a piezo crystal (quartz), every single dipole in every unit cell gets stretched. Therefore, the whole body get stretched. And the polarization increases.

Secondly, we do streched the random aligned domains! In every ferroelectric there are domains with mutual aligned inner polarizations. When c-site is longer than a and b, and we put a stress from c site, the unit cell should move 90° right? You can imagine hundred pens. When you grab them, they will align! So, the "body of pens" will strain in the "long-direction", thus we have a bigger net polarization due to the alignment of every unit cell / pen in c-direction.

The central issue is: Do the second point make a large strain? Or is the second point just describing the phenomenon of electrostriction? Or, none of them (or a mixture): There are domains, the induced stress let the domain move and therefore we can now do point 1: streching them! Do the movement of domains itself lead to a higher polarization (because c-site itseld is longer), or is the movement a condition for a higher polarization due to the further streching of the c-site?

Thank you !
 
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  • #2
The short version of the main issue is: Do the movements of 90° domains contribute to the typical large strain in piezo ferroelectrics upon an applied electric field? Do the movements of 90° domains contribute to the voltage upon a mechanical stress?
 
  • #3
Or let's say: What is the exact reason for the inverse piezoeffect (strain) in ferroelectrics?
And what is the exact reason for the pieoeffect in ferroelectrics?

Augmentation of Polarization in every unit cell or the movement of the domains resulting in augmentation in polarization?
 

1. What is the piezoelectric effect in ferroelectrics?

The piezoelectric effect in ferroelectrics is a phenomenon where certain materials, called ferroelectrics, can generate an electrical charge when subjected to mechanical stress or pressure. This is due to the asymmetrical arrangement of positive and negative charges within the material, which causes a displacement of charges when the material is compressed or stretched.

2. What are some examples of ferroelectric materials?

Some common examples of ferroelectric materials include quartz, tourmaline, barium titanate, lead zirconate titanate, and lithium niobate. These materials are often used in electronic devices such as sensors, actuators, and transducers due to their ability to convert mechanical energy to electrical energy and vice versa.

3. How is the piezoelectric effect in ferroelectrics measured?

The piezoelectric effect in ferroelectrics can be measured using a device called a piezoelectric sensor. This sensor consists of a ferroelectric material with electrodes attached to both sides. When pressure is applied to the sensor, it produces an electrical charge that can be measured by an external circuit. The magnitude of the charge is directly proportional to the amount of pressure applied.

4. What is the significance of the piezoelectric effect in ferroelectrics?

The piezoelectric effect in ferroelectrics has numerous practical applications in various fields such as medicine, aerospace, and consumer electronics. It is used in medical ultrasound machines, vibration sensors for aircraft monitoring, and touchscreens in smartphones and tablets. Additionally, the ability of ferroelectric materials to convert energy from one form to another makes them valuable for energy harvesting and storage.

5. Can the piezoelectric effect in ferroelectrics be reversed?

Yes, the piezoelectric effect in ferroelectrics can be reversed. This means that when an external electric field is applied to a ferroelectric material, it can cause a physical deformation or movement. This is known as the inverse piezoelectric effect and is the basis for technologies such as piezoelectric motors and actuators.

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