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  • 1
    facet.materialart.
    Unknown
    Properties of nearly perfect crystals at very low temperatures (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Data shows that the frequency stability of 5 MHz AT-cut quartz crystal oscillators is improved by lowering the temperature to 4.3 K. The resultant level of stability is apparently not, at this point, sufficient for a clock accurate to 1 part in 10(exp 17). However, many improvements are possible in the scheme presented here. These would involve better temperature regulation, better crystal mounting and vibration isolation, and lower temperatures. Below the lambda-transition at 2.17 K the residual bubbling of the bath would be eliminated. Thus, the prospect of a successful clock built on this scheme is not ruled out.
    Keywords: SOLID-STATE PHYSICS
    Type: NASA-CR-197221 , NAS 1.26:197221
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Unknown
    Solid state crystal physics at very low temperatures (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The properties of nearly perfect crystals was studied at cryogenic temperatures. A large Helium 3 and Helium 4 dilution refrigerator has been assembled, and is described. A cryostat suitable for cooling a 35 liter volume to .020 Kelvin was designed and constructed, together with instrumentation to observe the properties of nearly perfect crystals.
    Keywords: SOLID-STATE PHYSICS
    Type: NASA-CR-163240
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Unknown
    Properties of large nearly perfect crystals at very low temperatures (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A liquid helium cryostat of a size and construction unavailable commercially, was built for use in measuring the Q of several materials at milli-Kelvin temperatures. The design and testing of the cryostat is described as well as the design of the experiment vacuum chamber and adaptor for the dilution refrigerator insert. Theory, design, and testing are also discussed for the magnetic coils built to levitate the materials so as to isolate them and increase the measured Q. A four point suspension with capacitor end plates as the transducer was used to obtain preliminary Q measurements of 6061 aluminum alloy and single crystal silicon. Results are tabulated.
    Keywords: SOLID-STATE PHYSICS
    Type: NASA-CR-169894 , NAS 1.26:169894
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Unknown
    Solid state crystal physics at very low temperatures (1980)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The mechanical dissipation (Q) and resonant frequency of a 15 kg silicon crystal were measured at cryogenic temperatures. In the experiment described, temperature control was incorporated to reduce the time derivative of the temperature. The results of the Q measurements with and without this temperature control are quite different. Measurements of the resonant frequency of the fundamental longitudinal mode of the silicon crystal from 6 to 300 Kelvin are presented and discussed with respect to temperature, df/dT. It is observed that frequency increases as temperature decreases down to about 16 Kelvin, i.e. dt/dT is negative. However, below this temperature the frequency decreases as temperature decreases, i.e. dt/dT is positive. It is suggested that this behavior is related to the coefficient of thermal contraction of silicon, which changes sign at 18 Kelvin. Continuation of these experiments to 20 mK is discussed.
    Keywords: SOLID-STATE PHYSICS
    Type: NASA-CR-164548
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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