Abstract:We have shown that H02 forms transient complexes with the peroxovanadium(V) species but not with V02+. This is in agreement with the results of Samuni5 who detected ESR-active transients only in V(V) solutions containing peroxide. The presence of a faster decaying complex, which we have designated V05"O2H, was not detected by Samuni and Czapski6 in a perchloric acid medium. The faster rate of decomposition of V-05"•02 relative to V03+-02H reflects the respective oxidizing strengths of V05~a nd V03+. Also, high… Show more
“… 3 Ionic conductivity, σ, at room temperature vs the molar fraction of “conducting bonds”, I/(I + O). Key: ▿ = AgI−Ag 2 O−MoO 3 (σ from refs , , and 58 (extrapolated from low temperature), ▾ = AgI−(Ag 2 O·2B 2 O 3 ) (σ from ref ), ○ = AgI−(Ag 2 O.B 2 O 3 ) (σ from ref ), ▵ = AgI−(Ag 2 O·4B 2 O 3 ) (σ from ref ), · = AgI−Ag 2 O−P 2 O 5 (σ from refs , , ), ▪ = AgI−Ag 2 WO 4 (σ from ref ), and ◇ = α-AgI (σ from ref (extrapolated from high temperature)). The dashed line is the nonlinear best-fit with eq 2 (three parameters, Levenberg−Marquardt algorithm, R 2 = 0.99).…”
We propose a new model to explain the transport properties of AgI-based fast ion conducting glasses. The main factor affecting the ionic conductivity is the mobility of the Ag+ carriers, that is controlled by the Ag local environment. We model the ionic conductivity in terms of a percolation between a low-conducting phase (purely oxygen-coordinated sites), and a high-conducting one (iodine/oxygen, I/O, coordinated sites). The percolation takes place along pathways with fractal structure. The nature of the glass network, and namely its connectivity and dimensionality, plays a significant role only for low I/O values, originating the transport and thermal anomalies observed in borate and phosphate glasses.
“… 3 Ionic conductivity, σ, at room temperature vs the molar fraction of “conducting bonds”, I/(I + O). Key: ▿ = AgI−Ag 2 O−MoO 3 (σ from refs , , and 58 (extrapolated from low temperature), ▾ = AgI−(Ag 2 O·2B 2 O 3 ) (σ from ref ), ○ = AgI−(Ag 2 O.B 2 O 3 ) (σ from ref ), ▵ = AgI−(Ag 2 O·4B 2 O 3 ) (σ from ref ), · = AgI−Ag 2 O−P 2 O 5 (σ from refs , , ), ▪ = AgI−Ag 2 WO 4 (σ from ref ), and ◇ = α-AgI (σ from ref (extrapolated from high temperature)). The dashed line is the nonlinear best-fit with eq 2 (three parameters, Levenberg−Marquardt algorithm, R 2 = 0.99).…”
We propose a new model to explain the transport properties of AgI-based fast ion conducting glasses. The main factor affecting the ionic conductivity is the mobility of the Ag+ carriers, that is controlled by the Ag local environment. We model the ionic conductivity in terms of a percolation between a low-conducting phase (purely oxygen-coordinated sites), and a high-conducting one (iodine/oxygen, I/O, coordinated sites). The percolation takes place along pathways with fractal structure. The nature of the glass network, and namely its connectivity and dimensionality, plays a significant role only for low I/O values, originating the transport and thermal anomalies observed in borate and phosphate glasses.
“…3 with literature data for T g , 26,29,30,43,68 s dc , 26,[29][30][31]43,69 and E a . 26,[29][30][31]43,68,69 Starting with T g (Fig. 3a) we note that values reported in ref.…”
mentioning
confidence: 91%
“…The evolution of properties observed here as a function of AgI content is compared in Fig. 3 with literature data for T g , 26,29,30,43,68 s dc , 26,[29][30][31]43,69 and E a . 26,[29][30][31]43,68,69 Starting with T g (Fig.…”
“…One model proposes the formation of a structurally inhomogeneous glass where MX ͑mainly AgI͒ forms microdomains or clusters within the host matrix. [31][32][33][34][35] Movement of silver ions is thought to be facilitated by the formation of conducting pathways along the AgI microdomains. 2 A second model suggests that AgI is highly dispersed in interstices or voids controlled by oxygen atoms of the host matrix and that AgI enhances ionic conductivity by lowering the potential energy barriers within the glass.…”
The reflectance spectra of bulk superionic glasses xAgI-(1Ϫx)͓Ag 2 O-nB 2 O 3 ͔ with nϭ2, 0рxр0.65 ͑diborate͒ and nϭ0.5, 0.40рxр0.60 ͑pyroborate͒ have been measured in the infrared to investigate the structure of the boron-oxygen network and the nature of sites hosting silver ions. The analysis of the midinfrared spectra showed that the diborate network consists of borate triangles BØ 3 and BØ 2 O Ϫ , and borate tetrahedra BØ 4 Ϫ ͑Øϭoxygen atom bridging two boron centers͒. Similarly, it was shown that pyroborate dimers B 2 O 5 4Ϫ , orthoborate monomers BO 3 3Ϫ , and borate tetrahedra constitute the short-range order of pyroborate glasses. The relative abundance of these borate units was found to be affected by AgI doping in a way that can be described by the isomerization reaction BØ 2 O Ϫ BØ 4Ϫ for nϭ2 and the disproportionation reactionBoth reactions shift to the right upon increasing the amount of AgI. This influence of the doping salt on the glass structure causes the lowering of the glass transition and fictive temperature at which the structure of the supercooled liquid is frozen into the glassy state. A parallel study of infrared transmission spectra of thin films in the diborate family showed the presence of a background interference wave that affects strongly the relative intensity of bands due to borate tetrahedra and triangular units. This finding suggests that conclusions based on direct comparison of infrared spectra of thin film and bulk samples of the same composition should be drawn with caution. The study of the far-infrared profiles of glasses in the pyroborate series suggested that the majority of silver ions exist in two distributions of coordination environments; one is formed primarily by oxygen atoms provided by the borate network and the other is made mainly by iodide ions, without excluding the presence of mixed oxyiodide sites. The spectroscopic characteristics of silver iodide sites were found to change progressively with AgI addition and to point towards sites of tetrahedral coordination such as those found in crystalline AgI. However, for diborate glasses the far-infrared results suggest the presence of oxide, iodide, and mixed O/I environments for silver ions. Therefore, this study shows that the formation and organization of separate silver iodide sites in xAgI-(1Ϫx)͓Ag 2 O-nB 2 O 3 ͔ glasses depends on both Ag 2 O and AgI content. ͓S0163-1829͑99͒02030-5͔
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