GLASSY, CERAMIC, AND CRYSTALLINE LITHIUM ALUMINOSILICATES - CHARGE-TRANSPORT AND LOW-TEMPERATURE SPECIFIC-HEAT STUDIES

Using dielectric techniques in the frequency ranges from 0.01 Hz to 1 GHz and from 60 GHz to 3 THz, the transport, relaxational and vibratio nal motions of Li ions in stuffed aluminosilicates were studied. Sampl es investigated include the polycrystal beta-eucryptite, the ceramics Zerodur M and Zerodur as well as the precursor glass of the latter com pound. Conductivities similar in magnitude are found for all samples a t high temperatures. For temperatures well below ambient, local dielec tric relaxations are observed. Their appearances strongly depend on th e degree of the crystallinity of the host matrix. For the Zerodur samp les, the far infrared measurements yield evidence for excess absorptio ns at vibrational frequencies. In order to test whether these excitati ons are associated with an enhanced density of states, the specific he at of several aluminosilicates has been measured for temperatures betw een 5 and 50 K using the adiabatic Nernst method.