SECTION 4 - PHYSICAL-PROPERTIES OF UNIRRADIATED AND IRRADIATED CERAMICS - DIELECTRIC-SPECTROSCOPY OF ALUMINA CERAMICS OVER A WIDE FREQUENCY-RANGE

Aluminum oxide (either in single or polycrystalline form) is one of th e insulator materials with broad application in high radiation environ ments. Despite this demanding use, very different values for the diele ctric properties have been found in the literature before and after ir radiation. In order to obtain a reliable database, the dielectric prop erties of several unirradiated commercial alumina grades have been mea sured over a wide frequency (1 kHz to 15 GHz) and temperature range (1 00 to 300 K). Loss tangent differences over three orders of magnitude have been observed. The possible explanations and the role of some imp urities (mainly Mg and Fe) are analyzed. (C) 1998 Elsevier Science B.V .