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
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].