Low-temperature dielectric study of fused nitrates and other glasses

Abstract

Glasses of composition K-Ca-NO₃–H₂O exhibit a very broad dielectric loss maximum between 30 and 50 K (at 1·2 kHz) and a “plateau” region below 4 K where the loss factor is of order 10⁻³ and varies little with frequency or temperature. In these respects they resemble silicate glasses. Crystalline mixtures rich in KNO₃ have a sharp loss maximum near 40 K, and KNO₃-KNO₂ mixtures have a sharp loss maximum near 85 K. The nitrate glasses differ from silicates in that the plateau region extends to lower temperatures or higher frequencies. In this respect they more closely resemble organic glasses like polymethylmethacrylate. We find that the extent of the plateau region depends primarily on sound velocity, but the plateau loss value is governed primarily by the presence of mobile alkali ions.