[time-nuts] Quartz crystal aging and applied voltage

[Bob Camp]

Hi

Ummmm….. eerrrrr…..

Natural quartz is great stuff for making resonators. In many ways it's better than synthetic quartz. About the only thing natural is worse for is radiation. Natural quartz comes from all over the world. Most of the US supply comes from / came from Arkansas. If anything natural quartz with it's "thousands of years" growing process is lower stress and lower aging stuff. 

The whole synthetic quartz industry grew up simply to supplement the limited supply natural quartz. Remember - the only natural you can use is going to be entirely either right handed or left handed. That limits the amount you can find. That's not a purity thing, it's simply the crystallography of the lump you happen to have. The fact that it's not pre-oriented makes it slightly more difficult to work with. The number of blanks per pound will always be higher with synthetic. 

The whole issue with good stuff like humidity and crystals stopping dead was related to a precess that did not etch the crystals adequately after they were lapped. There were a few other issues, but that was the main one. Any quartz that will work as a resonator isn't going to be chemicaly affected by much of anything short of hydrofluoric acid. 

Bob


On Jun 30, 2013, at 7:14 PM, Brian Alsop <alsopb at nc.rr.com> wrote:

> Remember when WWII arrived, crystals were of poor quality and not in great supply.  The quartz crystal materials were all imported from South America and contained impurities.
> 
> They had the nasty habit of abruptly changing frequency or drifting. They also stopped oscillating when humidity got high.  Imagine yourself in the jungle calling for support during WWII and the transmitter goes dead due to the crystal.  Something had to be done.
> 
> This was solved quickly by growing "pure" crystals and developing the manufacturing process to do so.
> 
> We've come a long way baby.
> 
> Regards
> Brian
> 
> On 6/30/2013 23:04, Bob Camp wrote:
>> Hi
>> 
>> On Jun 30, 2013, at 2:44 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>> 
>>> Hi Bob,
>>> 
>>> On 06/30/2013 06:30 PM, Bob Camp wrote:
>>>> Hi
>>>> 
>>>> Ummm…. errrr…. not so much.
>>>> 
>>>> Ions in the lattice are part of the crystal structure. When you "move" them by sweeping you put stress on the quartz. That stress may take a *long* time to relax out. Since there is now a defect in the lattice (where the ion was) the stress may be relieved by an ion moving back to that location.
>> 
>>>> 
>>>> Quartz is swept to reduce it's radiation sensitivity. That's a big deal if you are going to put the oscillator in outer space or if you expect to need to use it when unexpected bright lights appear in the sky. Neither one is likely to be of interest in a typical basement lab. The levels involved also would drive you to radiation harden the rest of the oscillator circuit, not just the crystal.
>>>> 
>>>> There have been a series of papers on various influences on crystals. If the blank is an SC, it can be tuned by an applied DC voltage. Many precision parts have a DC short across the resonator for this reason. In that case, you would not see anything to drive an ion anyway.
>>> 
>>> NIST have been using this effect for precision phase modulations.
>>> 
>>> I don't agree that swept crystal has not been talked about. It is mentioned all over the precision crystal papers, it's there if you look for it. It however does not make much sense to discuss it for us, since we usually deal with complete oscillators and only rarely work with single crystals, and in that case very rarely of the quality where swept crystals occurs.
>>> 
>>> There is definitely more to it than sweeping the crystal.
>>> 
>>> Thanks Bob for the extra insight. The way sweeping works, won't a number of additional runs help to re-melt the crystal and help "ironing out" the dislocations in the crystal?
>> 
>> That's not the way it's done. One pass under bias, pull the ions to the edges. Cut off the edges. If you re-melt and re-grow the crystal you get a whole new batch of ions from the growing process.
>> 
>> Bob
>> 
>>> 
>>> Cheers,
>>> Magnus
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