Low-temperature microwave spectroscopy of Naβ -alumina

作者：Ulrich Strom, Manfred von Schickfus, Siegfried Hunklinger · 发表于：Physical review. B, Condensed matter · 年份：1982 · DOI：10.1103/physrevb.25.2405 · 被引用次数：22 · 研究领域：Ferroelectric and Piezoelectric Materials、Solid-state spectroscopy and crystallography、Microwave Dielectric Ceramics Synthesis

Low-temperature microwave conductivity data for $\mathrm{Na}\ensuremath{\beta}$-alumina have been analyzed in terms of the standard tunneling model of disorder-induced two-level states. In addition, the microwave dielectric constant has been studied as a function of temperature between 0.3 and 15 K for Na, K, and ${\mathrm{Na}}_{0.2}{\mathrm{K}}_{0.8}\ensuremath{\beta}$-alumina. The limitations of the tunneling model in describing the conductivity and dielectric-constant data, particularly at higher temperatures (> 5 K), are discussed. A direct relationship of the microwave conductivity to portions of the low-frequency loss in the ${10}^{2}$ - ${10}^{4}$-Hz region is established. It is shown that the low-frequency data require the existence of a temperature-independent conductivity term $\ensuremath{\sigma}\ensuremath{\sim}{\ensuremath{\omega}}^{n}$, where $n\ensuremath{\cong}1$ for $T<1$ K. A brief discussion is given of the possible origin of tunneling modes in $\ensuremath{\beta}$-alumina.