We have synthesized a Hierarchical WO3 structure and tested its chemoresistive gas sensing properties to some Volatile organic compounds. The results showed excellent sensitivity and selectivity to acetone. Apart from "research based on LiNbO3 and some other materials has shown strong evidence that the dipole moment of a polar molecule may interact with the electric polarization of some ferroelectric domains on the surface" in L.Wang Ph.D dissertation page 69 linked at the end of this passage , I did not find an explanation for selectivity of the as-synthesized powder to acetone. Since only epsilon phase of WO3 benefits from ferroelectric properties and this phase of the material is only obtained at cryogenic temperatures, I wonder why our powder is at least 3 times more sensitive to acetone in comparison with other VOCs. Does it have ferroelectric properties? How can I realize that the powder is ferroelectric?
https://web.stonybrook.edu/cnsd/FormServerTemplates/000000531.sbu.pdf
Hi Mostafa,
The first test you can do is to determine the crystal structure of your powder using X-ray diffraction. A ferroelectric material will have a non-centrosymmetric unit cell; conversely if you find your powder has a centrosymmetric structure then it is not ferroelectric. Secondly, you can measure the polarisation (P) as a function of applied electric field (E); a ferroelectric will exhibit a hysteresis loop.
Robert Lowndes
I think you should make a very thin pellet (0.5 -1 mm thickness) from the synthesized powder and measure the polarization of that pellet as a function of applied electric field by using a P-E loop tester. A ferroeletric compound will show saturation polarization and hysteresis in the polarization with increasing and decreasing electric field.
Hi Robert
First of all I appreciate your attention to the question. The powder has been characterized by XRD and the obtained XRD image was analyzed using X'Pert software. Your answer brings another question: How can it be realized from the obtained XRD pattern that the material unit cell is acentric and has ferroelectric properties? Do you know any special software for this purpose?
Mostafa Esmaeili
Hi Samar
Thank you for your attention. Unfortunately we do not have the facilities at the moment to do your proposed test.
Mostafa Esmaeili
Dear Samar
If your material shows complete P-E hystersis loop it is ferroelectric. From XRD you can not confirm wether it is ferroelectric or not.
@Gurvinderjit
What did I said earlier? I said the same thing that he needs to do P-E hysteresis measurement.
Actually Robert said that he can some signature if the material is ferroeletric or not. As most of the cases it has been found that materials with non-centrosymmetric crystal structure show ferroelectricity. Not true always and you can have extrinsic ferroelectricity though the material dose not show any non-centrosymmetric structure.
Is there any alternate method to obtain the P-E loops indirectly without using the PE loop tester?
Of course, although it requires some work.
Use i.e. google to find "sawyer tower circuit".
In the simplest option, if you have a thin samples, you can use autotransformer (AC control voltage 50/60 Hz in the range from 0 to 230) and a capacitor with high capacitance ~> a few micro-Farad (not electrolytic) and digital oscilloscope preferably with a waveform recording.
twenty years ago I was studing the ferromagnetic transformation of stainless steel from heavy oil fired boiler tubes due to carburization. The carburizated layer was very thin. I built a magnetic balance to increase the sensibility to detect carburized tubes and was very effective to detect qualitatively the presence of carburized layer on boiler tubes. The sample is placed near to the magnet and you can detect the movement of the balance. Magnetic Balance is very easy to built and maybe usefull. A schematic description is attached.
N.Orloff
How can I get your thesis??
Another important thing is that we found out capacitance of the as-fabricated sensor varies under gas exposure. Up to your experience is there any meaningful relation between gas type and capacitance variation ? It can be a brilliant idea to improve selectivity of metal oxide based gas sensor esp cross sensitivity is the most problematic challenge of this area.
Dear Mostafa,
You can try Rietveld analysis to find out if you have epsilon phase (non-centro symmetric) in your sample. If you read the full thesis of Wang, you will not say that epsilon phase can be "only" obtained at cryogenic temperatures. Another way to check for ferroelectricity is by doing magnetic measurements using SQUID. I certainly believe that you have high percentage of epsilon WO3 for acetone sensitivity. Do you mind posting your XRD pattern?
Rishabh Jain
To test existence of ferroelectricity in your sample.
Firstly your material should be a good insulator.
Should exhibit a phase transition in temperature dependent dielectric properties.
Should exhibit ferroelectric hysteresis loops.
these are some standard characteristics shown by a typical ferroelectric.
K. Sreenivas
Have temperature dependent dielectric studies from Impedance analyser this will enable you to determine the ferroelectric to paraelectric transition temperature. If you got a peak in dielectric constant vs temperature graph your material is sure ferroelectric.
Or you may do dirrectly ferroelectric measurments using ferroelectric testor. This will give you a PE hysteresis loop just like MH loop for ferromagnetic materials.
I have attached both papers First one for ferroelectric PE Loop second is temp. dependent dielectric studies.
Good Luck
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