Dielectric spectroscopy of alumina ceramics over a wide frequency range

Aluminum oxide (either in single or polycrystalline form) is one of the insulator materials with broad application in high radiation environments. Despite this demanding use, very different values for the dielectric properties have been found in the literature before and after irradiation. In order to obtain a reliable database, the dielectric properties of several unirradiated commercial alumina grades have been measured over a wide frequency (1 kHz to 15 GHz) and temperature range (100 to 300 K). Loss tangent differences over three orders of magnitude have been observed. The possible explanations and the role of some impurities (mainly Mg and Fe) are analyzed. (orig.)