Good work BB.
Just curious to know, is it because of polarization in the materials we see ferroelectric behavior or because the material is ferroelectric it gets polarized.
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Thank you Dharma, I think for the major difference between a ferroelectric material and a non-ferroelectric material (such as paraelectric or anti-ferroelectric materials) is that ferroelectric material has spontaneous polarization behavior. Please see fig.5. And for your question, as far as I know that every dieletric material can be "polarized" (with a external force, heat, electric field…), but not all of them has the spontaneous polarization.
If you still have further quetion about this, please let me know.
How one measure the ferroelectricity, I mean instrument used to measure it.
It depends on which property you are interesting in. If you are looking for a PE hysteresis curve, most people construct a simple circuit to measure hysteresis using a function generator and an oscilloscope. This approach was first used by Sawyer and Tower in 1929 to measure one of the earliest known ferroelectric materials, Rochelle Salt. Like the figure.
If you are interesing in the electrical properties, there are several different equipments to measure that. For example, a lots of researchers measure their ferroelectrics electrical properties by LCR meter. This is also the one I used to measure my sample's electrical properties (inductance, capacitance, resistance). The one I used is LCR meter 4284A
I am doing both test with polymer and polymer/nanocomposite materials in EIRC, locating at the ground floor of IMS. If you are interested, I am very glad to share my experience.
Hi,
I am wondering if you are using any reference capacitor like in the figure when you are characterizing the ferroelectric capacitor? From the capacitance information how do you extract the polarization (P)? And last question is what do you do with inductance of a ferroelectric capacitor, does it tell anything?
thanks.
Nice work BB. I was just wandering, what defines the "thickness" of the hysteresis loop (= the electric field that is necessary to apply in order to have zero polarization)?
Thanks Maria, I think I still don't quite understand about the describe of "the electric field that is necessary to apply in order to have zero polarization". Do you mean about the phenomena of how much external electric field to reach maximum polarization. Or maybe it just only I have not hear this yet, but I will keep lookng for the answer for your question. And post on the webpage when I found some anwser for this.
Actually, I was wandering about what defines how big the electric field will be for zero polarization (it corresponds to point F and its symmetric point in fig.5). Is it the material's structure or it depends on the electronic properties of the atoms of the lattice? For example, how does the field corresponding to zero polarizability change from PbTiO3 to BTiO3?
In the case of dipolar interaction, where does the greater contribution come from?
There seems to some inconsistency between the text and fig.6.
Good point, Maria. I think this figure is not so accurate for every situation. The magnitudes of different polarizations depend on frequency, temperature and material itself. Like I mentioned in the paragraph, if you measure the polarization of a dipolar substance at low frequency (w<109), then the dipolar polarization should be the dominant polarization provider in the material. In other word, if you measure it at high frequency, then the electronic should be the dominant one.
And I will try to find another better plot of the polarization V.S. frequency. Thanks.
hey Maria, sorry I can not find the more proper figure on other websites, so I draw the figure (follow the fig. 8.10 in the text book)
I hope it looks a little bit better.
Hi, Ching-Chang,
Good job! I am doing some ferroelectric properties study with polymers for my own research and I do find a lot of useful informations from the ferroelectric ceramic world. And there are some concepts that I am always confusing. They are paraelectricity and/or anti-ferroelectricity. Do you know how to differentiate them? Thank you!
hello Fangxiao,
Paraelectricity is the ability of many materials (specifically ceramic crystals) to become polarized under an applied electric field. Unlike Ferroelectricity; this can happen even if there is no permanent electric dipole that exists in the material, and removal of the fields results in the polarization in the material returning to zero. And Antiferroelectricity is a physical property of certain materials. It is closely related to ferroelectricity; In an antiferroelectric, unlike a ferroelectric, the total, macroscopic spontaneous polarization is zero, since the adjacent dipoles cancel each other out.
In another explaination, Paraelectricity occurs in crystal phases in which electric dipoles are unaligned (i.e. unordered domains that are electrically charged) and thus have the potential to align in an external electric field and strengthen it. In comparison to the ferroelectric phase, the domains are unordered and the internal field is weak. And for anti-ferroelectric materials, An antiferroelectric material consists of an ordered (crystalline) array of electric dipoles (from the ions and electrons in the material), but with adjacent dipoles oriented in opposite (antiparallel) directions (the dipoles of each orientation form interpenetrating sublattices, loosely analogous to a checkerboard pattern). This can be contrasted with a ferroelectric, in which the dipoles all point in the same direction.
By following figure, I hope it can provide you more useful information between their relationship.
Hi Ching-Chang Chung,
I am wondering if the hysteresis loops show deviations as a ferroelectric capacitor is electrically stressed continuously (endurance) and a very long time after they are stressed (retention). Do you thing this properties are enough to use them as non-volatile memories which requires more than 106 cycles and more than 10 years of retention.
Thanks.
Hi Gokhan,
I think Two of the major reliability concerns hampering the use of ferroelectric thin films in non-volatile memory devices are fatigue and imprint. Fatigue consists in the loss of remnant polarization with cumulative switching of the capacitor. If the remnant polarization falls below the detection threshold of the device, the memory cell becomes unreadable.
And the hysteresis loop will show deviations when it under stressed for a long time, The fatigue in ferroelectric films is mainly due to the pinning of domain walls by space charge near the boundaries of electrodes and structural defects such as microcracking and porosity. So, if you wanna have a good non-volatile memories you do have to consider the fatigue effect on the ferroelectric thin film.
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