Glasslike Two-Level Systems in Minimally Disordered Mixed Crystals

Abstract

THz spectroscopy is used to identify a broad distribution of two-level systems, characteristic of glasses, in the substitutional monatomic mixed crystal systems, Ba(1-x)Ca(x)F(2) and Pb(1-x)Ca(x)F(2). In these minimally disordered systems, two-level behavior, which was not previously known to occur, begins at a specific CaF(2) concentration. The concentration dependence, successfully modeled using the statistics of the impurity distribution in the lattice, points to a collective dopant tunneling mechanism.

Supercooling at Melt Growth of Single and Mixed Fluorite Compounds: Criteria of Interface Stability

“…As a result, after a primary crystallization of a continuous series of Ba 1-x Ca x F 2 fluorite solid solutions with a minimum in the liquidus curve at x < 0.5, during the cooling there occurs a high-T (at 900 o C) solid-state decomposition into a two-phase mixture of dilute CaF 2 and BaF 2 -based solid solutions (Chernevskaya, & Anan'eva, 1966;Wrubel et al, 2006;Zhigarnovskii & Ippolitov, 1969). The phase diagram of this system has been recently reviewed by Fedorov et al (2005) who showed it does not contain a continuous solid solution.…”

Effects of resonant phonon scattering from internal molecular modes on the thermal conductivity of molecular glasses

“…Amongst those, the behavior of the temperature dependence of the thermal conductivity ͑T͒ of glasses and disordered crystals continues to attract a significant research effort. 1 The most intriguing manifestation of the scattering of heat waves by either topological, 1 orientational, 2 chemical disorder, 3 defect crystals, 4 or even crystals with minimum disorder 5 concerns the quantitative similitude of ͑T͒ within a relatively wide range of temperatures ͑0.1-10 K͒, independent of the chemical composition. In stark contrast, most of our understanding of such phenomena relies on phenomenological constructs such as the two-level systems 1 ͑TLSs͒ or soft-potential 6 models ͑SPMs͒.…”