[time-nuts] Xtal Oscillator Aging

[Luis Miguel Brugarolas]

At Sunday, October 23, 2005 9:21 PM, Tom Clark wrote:
>   Going in the other direction, the mechanical resonant frequency
>   changes with time because, as the xtal vibrates, microscopic cracks in
>   the structure of the quartz break apart. Running at high power makes
>   the crystal generate these microscopic faults at a faster rate; this
>   then causes the oscillator to have poorer long-term stability. When an
>   xtal is left vibrating (oscillating) in an undisturbed environment,
>   the rate of cracking of the quartz decreases, and the oscillator is
>   said to "age" to its final frequency.
>   But if you subject that same crystal to a mechanical jolt will force
>   some new cracks and re-start the aging "diffusion" process. Ditto
>   turning the oscillator on & off or a thermal shock can aggravate the
>   aging.

Could someone confim or deny an idea I posted some weeks before about ageing 
is more predictable on free running oscillators than in disciplined ones?.
I read about it in a Simetricomm datasheet some time ago, but I would like to 
know experimental or theoretical explanation for that (or the contrary).
Best regards
Luis Miguel