The thermodynamic behavior of thickness-shear vibrations of a disc quartz piezoelectric plate of singly or doubly rotated orientations has been investigated. It has been shown the function has a particularly pronounced resonance called a thermodynamic resonance. The top of the resonance in the frequency range of less than 1 Hz for different quartz resonator designs and its character are responsible for a power spectral density burst of OCXO fluctuations with extremely small turning away from the carrier frequency. Practical recommendations are given as to the choice of the quartz resonator parameters which provide a minimum thermodynamic frequency instability effect in quartz crystal resonators.
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