Sources of pyroelectric crystal (LiTaO3 and LiNbO3)

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Grigory_Heaton
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Sources of pyroelectric crystal (LiTaO3 and LiNbO3)

Post by Grigory_Heaton » Sat Dec 03, 2016 4:46 am

I hope this is the right section for this. I've seen this subject discussed here before but it was on a completed project page.

I was wondering if anyone had any good sources of the small pyroelectric crystals LiTaO3 or LiNbO3 that aren't the very expensive $700 giant crystals you can buy from suppliers (and it seems that most are going to have a lower limit on purchase quantities for the smaller $50-100 wafer crystals). I was planning on trying to construct a small X-ray source/particle accelerator using one (like this http://www.rapp-instruments.de/index8.htm) (eventually when I manage to find a vacuum pump) as a relatively low cost way to maybe if everything works out get some small number of fusion reactions in the far future, as the 2005 UCLA team and the high school team on this forum have done in the past. I know PIR Motion Detector sensors contain some (and I'm planning on disassembling one as soon as it arrives in the mail to look for this), but I am fully expecting the crystals in these to be too small to be of any use. The only other option I've seen are SAW filters but none of these seem to list their pyroelectric material composition in the specsheets, and the only DIY Xray generator that uses one (linked above) doesn't list the filter they used.

Link to the pyroelectric fusion paper in case you haven't seen it: http://www.nature.com/nature/journal/v4 ... 03575.html
I find it a very interesting subject.

John Futter
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Re: Sources of pyroelectric crystal (LiTaO3 and LiNbO3)

Post by John Futter » Sat Dec 03, 2016 5:54 am

Grigory

we tried this at work
you need a good vacuum is backing pump and small diff pump to get good enough insulation.
yes it does produce x-rays for a split second and not very much of them crystal size, insulation, temperature differential, and temperature leakage all play a major part in success

Dan Knapp
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Re: Sources of pyroelectric crystal (LiTaO3 and LiNbO3)

Post by Dan Knapp » Sat Dec 03, 2016 10:50 pm

I bought some 3 cm dia x 1 cm thick LiTaO3 crystals back in 2005 soon after the Putterman group published the Nature paper. At that time the cheapest source I could find was Red Optronics. I don't recall the actual cost, but they were not cheap. Be sure you get the correct cut; Z-cut is what you want for the pyroelectric acceleration/fusion experiment.

AllenWallace
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Re: Sources of pyroelectric crystal (LiTaO3 and LiNbO3)

Post by AllenWallace » Tue Dec 06, 2016 6:48 am

When buying pyroelectric crystals, you need for them to be Z-cut. Crystals used for SAW filters are cut at an angle and won't work for your purpose. They also may be treated so that the surface charge doesn't accumulate.

Your best bet is AO modulators or Q switches. eBay currently has these priced under $100 each. You will have to become an mini-expert of these devices to understand if what you are buying will work for you. An eBay seller sells 'large' (but thin) lithium niobate crystals for about $25 . They are about the size if a microscope slide. I bought one but I have not the slightest idea if it is a Z-cut crystal.

I must admit, it quite fascinating to watch the arcs flash across the top to bottom of a pyroelectric crystal when you warm it up and cool it down.

Before you buy expensive crystals, I encourage you to experiment with the very cheap PZT devices. We all know that these are piezoelectric, but they are also pyroelectric. see http://www.ece.utah.edu/files/2014/07/x-ray-2.pdf

Grigory_Heaton
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Re: Sources of pyroelectric crystal (LiTaO3 and LiNbO3)

Post by Grigory_Heaton » Tue Dec 06, 2016 8:25 pm

Thanks for the help Allen.

It's my understanding that even if the crystal is not Z-cut, there will still be a Z face, it just will be very small if the crystal is a flat slide (for example in the SAW crystal from the Rapp Instruments page he used the thin edge of a SAW crystal as his Z face for the XRay tube). Because of this and the fact that you mentioned that the crystal produces visible discharges when heated up, it should be possible to determine the orientation cut of the crystal. The polarization of the crystal should occur across the Z- and Z+ faces - so if I am not misunderstanding something the arcs should go from one Z face to the other, which can show which side is the Z face.

When you heated the crystal up to observe the arcs, was it clear which faces the arcs were travelling between? If it's the large face then this crystal is the real deal.

Either way, thanks for that tip on the Ebay seller, I have asked the seller if he knows what kind of orientation cut the crystal is in. Even if that's unknown it's still a very good deal for LiNbO3 from what I've seen so far.

Edit: Seems that changing up my search criteria a bit on Ebay pulled up a decent thin Lithium Tantalate disk, which is the pyroelectric material used in the fusion report. $59 for a 0.2 mm thick disk.

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