1,721,021 research outputs found
Physical Review Letters
No full textIn a recent Letter, Roling et al. [Phys. Rev. Lett. 78, 2160 (1997)] proposed a novel scaling approach, requiring no arbitrary parameters, for the analysis of the ac conductivity resulting from ionic motion in glasses. However, this approach cannot be applied to alkali germanate glasses whose alkali content varies by more than a decade, since changes which occur in the ion hopping length that accompany the changing alkali content are not incorporated. Here, I show that these changes can be incorporated into a universally valid approach which successfully scales the ac conductivity of sodium germanate glasses as well as two additional ionic systems without the introduction of arbitrary parameters.183653-36568
Use of Bratwurst Sausage as a Model Cadaver in Introductory Physics for the Life Sciences Lab Experiments
No full text6367-3715
Physical Review Letters
No full textThe dielectric response of many materials exhibits universal behavior in the form of a power law frequency dependence of the ac conductivity. This response is seen in all types of structures both crystalline and amorphous and for all types of polarizing species including dipoles and ions. Here I demonstrate that for ionic materials the power law exponent decreases with decreasing dimensionality of the ion conduction pathways. Although percolation concepts such as random walks on a self-similar fractal lattice provide a qualitative explanation, experimental findings instead indicate that the dispersion is the result of localized ion motion occurring on an atomic length scale.5983-9868
Physical Review. B, Condensed Matter and Materials Physics
No full textWe report measurements of the dielectric loss in a series of monovalent metaphosphate glasses at cryogenic temperatures. An analysis of the scaling properties of the dielectric response reveals a nonionic contribution to the loss present only in glasses for which the conduction cation is constricted by the oxide network. As a result, our effort to examine recent conflicting reports for the cation mass dependence of the nearly constant loss in ion-conducting, disordered materials has been obfuscated. Instead, it is shown how this nonionic contribution may explain additional conflicting observations for the nearly constant loss reported over the last 10 years.131342067
Physical Review. B, Condensed Matter and Materials Physics
No full textThe ac conductivity resulting from ion motion in glasses displays a power-law frequency dependence characterized by an exponent n<1. Recently, it was suggested that this exponent depends upon the dimensionality of the local cation conduction space, such that n decreases with decreasing dimensionality. Here, I report measurements of the ac conductivity of two metaphosphate glass systems. The first are the superionic glasses formed by doping AgI into AgPO3. The second are the alkali-metal metaphosphate glasses, MPO3, where M=Li, Na, K, Rb, or Cs. In both glass systems, the conductivity exponent varies with expansion of the phosphate chains which comprise the glass network. In the AgI-doped glasses, n increases with increasing expansion of the network, whereas in the alkali-metal series, n decreases with the expansion. However, when n is considered as a function of the “constriction” of the cation (i.e., the cation size relative to the chain separation), this exponent behaves similarly for both glass systems, decreasing with increasing constriction of the cation. This decrease is proposed to result from a reduction in the coordination of the cation’s local conduction space caused by increased constriction.2114507-145166
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
No full textWe report static and dynamic light-scattering measurements of aqueous glucose solutions near their glass transition. Photon correlation spectroscopy reveals two relaxation processes present in the supercooled liquid: a nonexponential and nonhydrodynamic, α-relaxation occurring at short times and an exponential and hydrodynamic relaxation occurring at longer times. The slow relaxation is seen only in the polarized scattering geometry and is in many ways identical to the “ultraslow” mode recently observed by others in specially annealed molecular glass-forming liquids and attributed to the formation of long-range density correlations or “dynamic clusters.” Static light scattering confirms the existence of excess scattering in our glucose solutions that is consistent with clusters in a size range between 30 and 60 nm. The size of the clusters varies with the water content and the clustering appears to be associated with the percolation of a hydrogen-bonded glucose network.1011505-1 - 011505-77
Physical Review. B, Condensed Matter and Materials Physics
No full textIn the literature, the electric modulus representation has been used to provide comparative analysis of the ion transport properties in different ion-conducting materials. In this paper we show that the modulus representation is not a suitable tool for such purposes. Our arguments derive from an examination of the scaling properties of both the ac conductivity σ*(ν) and the modulus M*(ν) which demonstrates how scaling that is inherent in σ*(ν) is lost in M*(ν) by inclusion of the high frequency permittivity ɛ′(∞), the latter quantity being unrelated to ion transport processes. Furthermore, we show how highly regarded shape changes of the modulus that occur with varying ion concentration are merely a manifestation of including ɛ′(∞) in the definition of M*(ν). We conclude then that the electric modulus formalism has resulted in misleading interpretations of the ion dynamics and, hence, should be discouraged.243016
Physical Review. B, Condensed Matter and Materials Physics
No full textA study of the viscoelastic relaxation in anhydrous liquid P2O5 is reported. Properties of the time decay of the dynamic structure factor, including the average structural relaxation time and the stretching exponent, were obtained for temperatures from 850 °C to near the glass transition Tg=419 °C using photon correlation spectroscopy. Analysis indicates that P2O5 is a strong glass-forming liquid but one that exhibits an abnormally nonexponential relaxation near Tg. The viscoelastic behavior of P2O5 is compared with that of its alkali-metalmodified metaphosphate counterparts NaPO3 and LiPO3, as well as with the mechanical relaxation of chalcogenide glasses, to demonstrate common patterns in dynamical behavior presumably arising from changes in the average connectivity of the glass structure.2020201-1 - 020201-47
Journal of Chemical Physics
No full textWe report the first ever photon correlation spectroscopy performed on single alkali and mixed alkali metaphosphate glasses at refractory temperatures above the glass transition. We find not only a significant decrease in the glass transition temperature but also a decrease in fragility for the mixed alkali composition as compared with the single akali glasses. We argue that structural relaxation in these polymeric oxide glasses is largely controlled by the cross linking cations and that the changes in fragility that we observed are a reflection of changes in the cooperativity of structural relaxation wrought by the substantial decrease in the ion mobility that accompanies the mixing of alkali ions2450212
- …
