Analysis of the susceptibility minimum observed in 0.4Ca(NO3)(2)-0.6KNO(3)by dielectric spectroscopy and light scattering

Citation
R. Casalini et al., Analysis of the susceptibility minimum observed in 0.4Ca(NO3)(2)-0.6KNO(3)by dielectric spectroscopy and light scattering, J CHEM PHYS, 112(11), 2000, pp. 5181-5189
Citations number
66
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF CHEMICAL PHYSICS
ISSN journal
00219606 → ACNP
Volume
112
Issue
11
Year of publication
2000
Pages
5181 - 5189
Database
ISI
SICI code
0021-9606(20000315)112:11<5181:AOTSMO>2.0.ZU;2-Q
Abstract
An intriguing feature of the relaxation of glass formers is the broad minim um in the dynamic susceptibility spectrum, lying intermediate between the h igh frequency vibrational absorption (or Boson peak) and the slower, temper ature-dependent structural relaxation and diffusion. As first shown by Lunk enheimer [Phys. Rev. Lett. 77, 318 (1996)], high frequency dielectric spect ra can be accounted for by invoking a temperature-dependent, frequency-inde pendent contribution ("constant loss") to the loss spectrum. Herein, we ana lyze dielectric relaxation and light scattering data for 0.4Ca(NO3)(2)-0.6K NO(3) (CKN), which exhibit broad minima at GHz to THz frequencies. Over a w ide temperature range, the spectra can be accurately described by the addit ive superposition of a constant loss to the structural relaxation and the B oson peak. Moreover, the temperature dependence of the constant loss term i s the same for the two spectroscopies. The behavior of the constant loss in ferred from this analysis is minimally affected by the details of the fitti ng procedure, demonstrating the robustness of the method. We also show that dielectric relaxation data for a silver iodide-silver selenate glass confo rm to the predictions of mode coupling theory, even though a liquid state t heory is not obviously applicable to a glassy ionic conductor. This undersc ores the value of alternative interpretations of the high frequency dynamic s in glass-forming liquid, including contributions from a constant loss suc h as described herein. (C) 2000 American Institute of Physics. [S0021-9606( 00)70311-4].