Single Alkali Glasses Research Articles

Ionic transport in mixed sodium rubidium germanate glasses

Ionic conductivity measurements have been made as a function of temperature and Na/Rb ratio on four series of x(Na, Rb) 2O: (1− x)GeO 2 glasses where x≈0.09, 0.15, 0.19 and 0.29. The three series with x⩾0.15 exhibit the common characteristic of mixed alkali glasses; a maximum in the enthalpy for conductivity, H m(max) for glasses with Na ( Na + Rb) ≈ 0.5. The magnitude of the mixed alkali effect, as measured by the difference between H m (max)and the enthalpies for conductivity of the single alkali glasses of the same series, could not be correlated with changes in the glass network structure or the type and concentration of charge compensating centers in the glass network. The pre-exponential factors for the conductivity are analysed to obtain values of the physical correlation factor or percolation efficiency, f t. In each of the four series f t was a maximum at Na ( Na + Rb) ≈ 0.5 and based on the changes in the percolation effeciency of the mixed alkali glasses a model is proposed to explain the mixed alkali effect.

Distribution of Cs + ions in single and mixed alkali silicate glasses from energy dispersive x-ray diffraction

The present study uses the energy dispersive X-ray diffraction (EDXD) technique to determine the average local distributions of Cs+ ions in silicate glasses with the compositions Cs2O·3.4 SiO2 and (0.405 Cs2O + 0.595 Na2O) · 3 SiO2. The data show that the local structure around Cs+ ions is very similar in the single and mixed alkali glasses, despite large differences in their ionicconductivities. No evidence of pairing or mixing of Cs+ and Na+ ions is seen, suggesting that the different ions may segregate submicroscopically into separate regions in the glass.

ChemInform Abstract: TRACER DIFFUSION AND ELECTRICAL CONDUCTIVITY IN SODIUM‐RUBIDIUM SILICON SULFIDE GLASSES

AbstractEs werden die Tracer‐Diffusionskoeffizienten von nNa und "Rb und die elektrische Leitfähigkeit von O.56(Na, Rb)2So0.44 Sisz‐Gläsern in Abhängigkeit vom Na/Rb‐Verhältnis und von der Temp. gemessen.

Tracer Diffusion and Electrical Conductivity in Sodium‐Rubidium Silicon Sulfide Glasses

The tracer diffusion coefficients of 22Na and 86Rb and electrical conductivity were measured in a series of 0.56(Na, Rb)2S.0.44SiS2 glasses as a function of the Rb/Na ratio and temperature. The data were used to calculate the Haven ratio as a function of the Rb/Na ratio. The Haven ratio at 149.6°C increases from ∼0.3 in single‐alkali glasses to ∼0.80 for intermediate compositions. The results are consistent with a single jump mechanism involving jumps of alkali ions between unoccupied sites. The observed correlation effects arise through interactions between alkali ions and charge‐compensating centers in the glass network. The charge‐compensating centers are thought to correspond to non‐bridging oxygen ions in some oxide glasses and to nonbridging sulfur ions in sodium‐rubidium silicon sulfide glasses.

Tracer diffusion and electrical conductivity in sodium-cesium silicate glasses

The tracer diffusion coefficients of 22Na and 137Cs, and the electrical conductivity have been measured in the (Na, Cs) 2O:3SiO 2 glasses as a function of temperature and Cs/Na ratio. Complex impedance analysis was used for the conductivity measurements. The Haven ratio at 396.5°C increases from 0.3–0.4 in single-alkali glasses to 0.8 for the mixed-alkali compositions. The results are explained in terms of a single-jump mechanism; interactions between alkali ions and non-bridging oxygen ions, and between different alkali ions, produce the observed correlation effects.

Mechanism of Glass Darkening by a Low Pressure Mercury Discharge

A study was made of the darkening of sodium and potassium silicate glasses by a low pressure mercury discharge, using electron spectroscopy, Rutherford backscattering, and transmission electron microscopy. Initial changes in glass exposed to a mercury discharge are twofold: (i) mercury from the discharge penetrates very rapidly into the glass to depths of the order of 1 nm. (ii) Alkali ions migrate more slowly away from the surface in a photoelectric field that is caused mainly by trapping of photoelectrons. However, mercury entering the glass does not replace alkali ions. Rather, the mercury penetrates into voids in the glass network that are sufficiently close to the surface. From this “surface reservoir” mercury migrates slowly deeper into the glass. This migration is slower in mixed than in single alkali glasses. We assume that mercury migrates as ions in a photoelectric field, assisted by photoelectrons. Ultimately the mercury ions are reduced by photoelectrons to atoms that agglomerate into droplets of metallic mercury reponsible for glass darkening. A mercury discharge provides not only (i) mercury ions and (excited) atoms entering the glass and (ii) photons, creating a photoelectric field in the glass. The discharge also provides (iii) low energy electrons flooding the glass. The latter greatly enhance the strength of the photoelectric field in the glass by recombination with photoholes in the glass near the surface. As regards the effect on the darkening of the glass composition, not only the overall composition is considered (e.g., conductivity, molar volume, shear modulus), but also superficial changes in the composition.

Effect of H2O Vapor on the Internal Friction of Binary Alkali Silicate Glasses

Internal friction and shear modulus of Na, K, and Li disiticate glasses were measured by a torsional pendulum as a function of H2O vapor treatment at T=300°C. H2O produced changes in the acoustic spectra (between—100° and 400°C and f=0.5 Hz) similar to the mixed‐alkali effect which appears upon introduction of a second alkali to a single‐alkali glass. An Na2O·2SiO2 glass free from the common nonbridging oxygen relaxation was produced.

Application of the Rheovibron to inorganic glass problems I. The mixed alkali effect loss spectrum

A mechanical spectrometer with four decade frequency range has been used to characterize the isothermal mechanical loss spectrum of a mixed alkali silicate glass. The half width of the mechanical loss spectrum is very much greater than that for electrical relaxation at the same temperature despite the fact that both relaxations are due to alkali ion motion. It is suggested that the difference, which is also present in single alkali glasses is primarily a consequence of the fact that the mechanical relaxation is by nature a secondary relaxation (probably one of a sequence of broad secondary relaxations) while the electrical relaxation is a primary relaxation insofar as it is the process producing the largest of all changes of electrical modulus.

Ionic jump processes and high field conduction in glasses

A theory of multiple-ion jumps is proposed to explain the large apparent jump distances which have been calculated from high field conduction in glasses. An analysis of published data on correlation coefficients suggests that multiple ion jumps up to about four ions at a time may occur in single-alkali glasses. In mixed-alkali glasses such processes are shown to be less probable. Measurements of high field conductivity were made on both single- and mixed-alkali glasses, using blown membranes between N/10 acid solutions. The onset of departures from Ohm's law occurred at fields of about 10 7 V m −1 from which a jump distance of about 25–30 Å is calculated. This is too large for the proposed multiple-ion jump processes suggested, and, furthermore, the high field currents followed the Poole-Frenkel (PF) law. An alternative theory is given in which the PF law is derived for ionic migration: shallow coulombic potential basins are assumed to be distributed throughout the volume of the glass, owing to non-bridging oxygens whose charge is not balanced by cations on adjacent sites.

Multichannel conduction in alkali silicate glasses

The qualitative change of the electrical conduction of alkali silicate glasses with alkali mixing is discussed in connection with dielectric and mechanical relaxation. The observed conduction is understood as the additive effect of two kinds of independent diffusion processes — I and II. In single alkali glass, diffusion process-I is always observed as the dominant conduction process. However, when one alkali is progressively substituted by another, the dominant conduction process is altered from diffusion process-I to II. In the mixed alkali glass containing equal amounts of two alkali ions, diffusion process-I disappears, so that only diffusion process-II is observed. Consequently, it becomes evident that the mixed alkali effect is not only the successive change of conductivity, but the alternation of the dominant conduction process.

Infrared spectra of double-alkali silicate glasses

Infrared reflection spectra have been taken of bisilicate glasses in which one alkali oxide (Na2O, K2O) is gradually replaced by another while their total content is kept constant, and the electrical conductivity and density, of these glasses have been determined. The spectra of single-alkali glasses containing 16–20% of alkali and whose structure, according to some authors, is similar to that of bisilicate glasses, are also included. The main characteristic features of the spectra of double-alkali glasses do not confirm this assumption, but indicate that their structure approximates that of single-alkali glasses; nevertheless, the parts composing the microheterogeneous structure have an altered composition as compared with that of single-alkali glasses. Electrical conductivity passes through a minimum for all three combinations of the alkali oxides, while density passes through a weak maximum in the case of sodium-potassium glasses only.