DIELECTRIC CONSTANT AND LOSS MEASUREMENTS ON HIGH-TEMPERATURE MATERIALS

Abstract

Measurement techniques for the frequency range 100 to about 2.5x10 to the 10th power are discussed for temperatures to 1650 C. These include the use of bridges, resonant circuits, standing-wave methods, and resonant cavities. Data on crystals of Al2O3, Cr2O3, MgO, LaAlO3, Y2O3; on multicrystalline bodies of Al2O3, BeO, MgO, Mg2SiO4, Ta2O5, ThO; on glass ceramics, silica glass, and BN are presented over smaller temperature and frequency ranges. Pyrolitic BN has a low loss tangent (o.0004 at 1375 C, 4.8x10 to the 9th power cps) and a low temperature coefficient of dielectric constant. Some aluminas and silicas exhibit loss tangents of ca. 0.0006 at 1000 C in the microwave region. Microwave losses are due partly to the charge transfer responsible for low-frequency conductivity and to the vibration spectra of infrared absorption. Both losses are increased by the addition of impurities.