Capacitance stability of ruby muscovite mica

The paper discusses short-time stability of dielectrics in general, and describes measurements of capacitance variations of mica with temperature and air pressure. The measurements are confined to mica plates and do not deal with finished mica capacitors. The results of the work show that short-term stability of mica depends largely on the plates being free from gas inclusions. The capacitance change of flawless mica over a temperature range 25¿95 deg C is substantially linear and cyclic, and a single temperature-coefficient figure defines the dielectric behaviour adequately. The measured coefficient figures show an even spread from +6×10¿6 to +40×10¿6. Mica plates with gas inclusions produce irregular and mostly very large changes of capacitance with temperature and particularly with air pressure.