I am using LiTaO3 cyrstals to study on their pyroelectric behavior. We've used electrom beam evaporator to cover the surfaces with Au (for conductivity). And now I'm a bit concerned and need to see if they still functioning. Has anybody done something like that before?
You should preferably have thin slab of LiTaO3 ( say 0.2 to 0.3mm thick).
Area can be around 5mm x 5mm) or even more.
Electrode the opposite surfaces.
1) You can us the well know Byer and Roundy method for the determination of the pyroelectric coefficient, which has been the oldest and the most original method.
You will find many paper on this technique.
2) You may need some basic apparatus. ( a good furnace, and an (electrometer)
and a three therminal sample holder.
- A good furnace with a controlled rate of heating. (say 1.5 to 2 deg C/min.
Now since you are using LiTaO3, you may have to go to very high temperaturs, because i thas a very high transition temperature.
Before you do your experiments, I would suggest try to study a simple TGS crystal, which has a low transition temperature of only 50 deg C. and first learn how to make the pyroelectric current measurements, and detemine the pyroelectric coefficient.
A notmal simple furnace which can go upto 100 deg C will be enough, but you have to control the rate of heating (1 to 1.5 deg C/min). Once you understand these measurements).
Then you will need a better furnace which can go to higher temperatures, and study your LiTaO3 crystal.
2) Alternate laser based methods like the Chynoweth method is also good, and you need different kinds of apparatus, and must collect all the relevant papers, and understand the method of measurement, and interpretion of the data.
K. Sreenivas
This might me helpful for you;
E. Theocharous, C. Engtrakul, A. C. Dillon, and J. Lehman, "Infrared responsivity of a pyroelectric detector with a single-wall carbon nanotube coating", Applied Optics Vol. 47, Issue 22, pp. 3999-4003 (2008).
I've got LiTaO3 crystals, each 4.0x2.0x0.5 mm in size. They are coated with 10 nm Cr and 100 nm Au and soldered to PCB boards for testing.
I've done something like the following: I couldn't make the calculations with the way I did it but just to see the respond, I made the connections between the grounds of the PCB boards and the power supply. I've used a simple broadband IR Led (just for heating actually), gave it around 20 V. Put the probes of the oscillator to the crystals and then basically watch the oscillator's screen while I let the IR Led to heat the crystal and then I've removed it.
I've seen the responding waves from all of them, albeit differently.
-Two of them gives a reverse response (when heated, the wave goes down and the other way around when it is cooled). The direction of the Z axis may be the cause of that, but I'm not so sure.
-Another two gives a voltage without the presence of IR Led, there are nothing connected to them but every time I touch the surface with the oscillator's probes, I get a peak around 150 mV and then it slowly stables around 30 mV, but not to 0. I know it shouldn't be possible since they are open to the environment and need to be neutralized when there is no change. Although it could be coating related, they are not purely identical from what I've seen under the microscope.
I'm trying to figure those out. Meanwhile, to calculate the coefficient and responsivity, I will use what you've so kindly suggested. Thank you for your reply.
And thank you for the article, since I'm also researching about coating materials (Because I'm worried about the gold's reflectivity), it would be a good reference.
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