Conductivity Of Phosphate Glasses Research Articles

Structure–polaronic conductivity relationship in vanadate–phosphate glasses

AbstractThis work provides new insights into the nature of the polaronic transport in xV2O5–(100−x)P2O5, 41 ≤ x ≤ 89 mol% glasses from analysis of their conductivity over a wide range of frequencies and temperatures, and correlation of the electrical parameters to the structural models of these materials. The results show that the linear increase in direct current (DC) conductivity with the increase in V2O5 could be related to the formation of a vanadate subnetwork, which is characterized by a length distribution of V–O bonds and variations in linkages between different vanadate units. Such a structurally complex network offers multiple conduction pathways which are favorable for polaron hopping. The Summerfield scaling of conductivity spectra reveals a temperature‐invariant mechanism of polaron transport for all glasses and the same local structural environment of polarons at higher V2O5 contents due to the same ratio of vanadate units present in the network. Also, this study highlights the similarities and differences in the nature of the polaronic transport of vanadate–phosphate glasses and other polaronically conducting phosphate glasses containing WO3, MoO3, and Fe2O3, and pins down a pivotal role of the glass structure in electrical processes in these materials.

Glass structure as a driver of polaronic conductivity in phosphate glasses containing MoO3 and WO3

Structurally governed polaronic conductivity in phosphate glasses containing tungsten and molybdenum oxides.

A significant enhancement of sodium ion conductivity in phosphate glasses by addition of WO3 and MoO3: the effect of mixed conventional-conditional glass-forming oxides.

Ion conducting oxide glasses are attractive materials for application in various electrochemical devices and an understanding of the structure-transport properties relationship is crucial for their development. An interesting effect of glass structure on the dynamics of mobile ions is the mixed glass-former effect which causes a non-linear change of ionic conductivity when glass-forming oxides get gradually substituted. Here, we report a strong, positive effect of structural changes on the conductivity of sodium ions in two glass systems 40Na2O-xMoO3-(60-x)P2O5 and 40Na2O-xWO3-(60-x)P2O5; x = 0-50 mol% where a conventional glass-forming oxide (P2O5) is gradually replaced by WO3/MoO3 which are conditional ones. In both glass systems, the compositional change in DC conductivity is non-linear, with the maximal increase of four orders of magnitude in the case of WO3 and three orders of magnitude in the case of MoO3. This significant enhancement of ionic conductivity is related to the formation of mixed phosphate-tungstate and phosphate-molybdate units in the glass network. The facilitating effect of these structural units on sodium ion dynamics is also observed in the changes of the shape of frequency-dependent conductivity and in the values of typical spatial extent of diffusion of sodium ions known as the Sidebottom length.

Thermal stability and proton conductivity of densely proton injected phosphate glasses containing rare-earth elements

• Effects of rare-earth element species in proton conducting phosphate glasses were studied. • Tg and glass structures were almost identical irrespective of the rare-earth element species. • Thermal stability was found to be significantly dependent on the rare-earth element species. • Surprisingly, the glass containing dy was stable up to 600 °C. • The glass containing dy exhibited proton conductivity of 4 × 10 −3 Scm −1 at 550 °C. Sodium ions in 25NaO 1/2 –3MgO–7 Ln O 3/2 –3GeO 2 –62PO 5/2 (mol%, Ln = La, Nd, Gd, Dy, Y, Yb) glasses were electrochemically substituted with protons with a substitution rate higher than 90% by using an Alkali-Proton Substitution (APS) technique.. Effects of rare-earth element species on various properties were investigated, such as the glass transition temperature (Tg), structure, thermal stability, and proton conductivity. Whereas Tg and glass network structures were almost mutually identical irrespective of the rare-earth element species, their thermal stability as evaluated from the onset temperature of weight loss during heating was found to be significantly dependent on the rare-earth element species. The glass containing Dy after APS exhibited the highest thermal stability among the glasses: it was stable up to 600 °C, which is ca. 370 °C higher than its Tg, without crystallization. Thermal stability depending on the rare-earth element species was related to the difference in the structure between the glass and the crystalline phase that precipitated from the glass. The proton conductivity was almost independent of the rare-earth element species. Therefore, the glass containing Dy which exhibited the highest thermal stability among the glasses exhibited the highest proton conductivity of 4 × 10 −3 Scm −1 at 550 °C.

Scaling features of conductivity spectra reveal complexities in ionic, polaronic and mixed ionic-polaronic conduction in phosphate glasses

The scaling behaviour of six series of mixed ion-polaron glasses with the composition xWO3/MoO3-(30–0.5x)Li2O/Na2O/Ag2O-(30–0.5x)ZnO-40P2O5, 0 ≤ x ≤ 60 mol%, has been studied using Summerfield and Sidebottom scaling procedures that are model free. The validity of the Sidebottom scaling procedure for each individual glass confirms that all glasses obey time-temperature superposition principle implying that the conduction mechanism does not change with temperature. On the other hand, Summerfield scaling is not found valid for all glasses. First, this deviation is observed in all glasses containing Li2O up to 20 mol% of MoO3/WO3. We relate this result to a non-typical interaction of Li+ ion with the compact zinc phosphate network resulting either in change of its hopping distance or in available conduction pathways for it as a function of temperature. Second, non-Summerfield scaling was also observed for glasses containing Li2O/Na2O/Ag2O with about 30 to 40 mol% of WO3. Thus, the origin of this deviation lies in the significant amounts of both types of charge carriers - ions and polarons, and their differently thermally activated mobilities.

Scaling Features of Conductivity Spectra Reveal Complexities in Ionic, Polaronic Andmixed Ionic-Polaronic Conduction in Phosphate Glasses

The scaling behaviour of six series of mixed ion-polaron glasses with the composition xWO3/MoO3-(30-0.5x)Li2O/Na2O/Ag2O-(30-0.5x)ZnO-40P2O5, 0≤x≤60 mol%, has been studied using Summerfield and Sidebottom scaling procedures that are model free. The validity of the Sidebottom scaling procedure for each individual glass confirms that all glasses obey time-temperature superposition principle implying that the conduction mechanism does not change with temperature. On the other hand, Summerfield scaling is not found valid for all glasses. First, this deviation is observed in all glasses containing Li2O up to 20 mol% of MoO3/WO3. We relate this result to a non-typical interaction of Li+ ion with the compact zinc phosphate network resulting either in change of its hopping distance or in available conduction pathways for it as a function of temperature. Second, non-Summerfield scaling was also observed for glasses containing Li2O/Na2O/Ag2O with about 30 to 40 mol% of WO3. Thus, the origin of this deviation lies in the significant amounts of both types of charge carriers - ions and polarons, and their differently thermally activated mobilities. Finally, based on a comparison of master-curves of all glasses with varying fractions of Li2O/Na2O/Ag2O and MoO3/WO3 we identify varied effects of the transition metal oxide on the transport of mobile ions as also the presence of mixed ion-polaron conduction.

Influence of Immobile Ions on the Length Scale of Ion Transport in Conducting Phosphate Glasses

We have reported the effect of immobile ions on the ion transport in conducting lithium phosphate glasses for different doping concentrations and glass modifier to glass former ratio. The composition dependence of the conductivity of these glasses has been compared with that of the ion conducting silver phosphate glasses. We have obtained microscopic length scales, such as mean square displacement of the center of charge of mobile ions and spatial extent of the localized motion of mobile ions from the conductivity and the dielectric spectra. We have observed a direct correlation between these microscopic length scales of the ion dynamics and the different structural units of the phosphate glass network.

Fast ion conducting phosphate glasses and glass ceramic composites: Promising materials for solid state batteries

Fast ion conducting (FIC) phosphate glasses and glass ceramic composites have gained considerable importance due to their potential applications in the fabrication of solid-state batteries and other electrochemical devices. We, therefore, present an overview on various types of FIC glasses and glass ceramic composites. Silver phosphate glasses doped with different weight percent of lithium chloride (1, 5, 10 and 15wt.%) were synthesized by melt quenching technique. The Ag2O–P2O5–(15wt.%) LiCl glass exhibited the maximum electrical conductivity (σ=8.91×10−5Scm−1 at room temperature and 4.16×10−3Scm−1 at 200°C). Using this glass as an amorphous host material, glass–ceramic composites of Ag2O–P2O5–(15wt.%) LiCl:xAl2O3 (x=5–50wt.%) were prepared. The ionic transference number, electrical conductivity, ionic mobility and carrier ion concentration of the synthesized samples were measured. Ag2O–P2O5–(15wt.%) LiCl:(25wt.%) Al2O3 composite system exhibited the maximum σ value (σ=3.32×10−4Scm−1 at room temperature and 2.88×10−2Scm−1 at 200°C ). Solid‐state batteries using undoped Ag2O–P2O5 glass, Ag2O–P2O5–(15wt.%) LiCl glass and glass ceramic composite containing 25wt.% Al2O3 as electrolytes were fabricated. The open circuit voltage (OCV) values and discharge time of these cells were measured and compared. It is found that the glass ceramic composites show enhanced ionic conduction, better OCV value and discharge characteristics.

Ion conducting phosphate glassy materials

Fast ion conducting (FIC) phosphate glasses have become very important due to a wide range of applications in solid-state devices. We present an overview on silver based fast ion conducting phosphate glasses. Silver phosphate glasses containing chlorides of some metals viz; Li, Na, Mg, Pb and Cu [Ag 2O–P 2O 5– xMCl y , where x = 0, 1, 5, 10 and 15 wt% and y = 1 when M = Li or Na and y = 2 when M = Mg, Pb or Cu] have been synthesized by melt quenching technique. Studies on these glassy materials characterized by X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetric techniques and ion transport measurements are presented. The FT-IR studies support the formation of P–O–M linkages. The values of glass transition temperature ( T g) of the glassy materials containing lithium or sodium chloride have been found to decrease with increasing dopant concentrations indicating expansion of the glassy network. On the other hand, the T g values increase with increasing magnesium, lead or copper chloride concentrations in silver phosphate glasses. This indicates an increase in cross–link density and enhanced chemical durability of these glassy materials. Ion transport studies suggest that the values of electrical conductivities of the metal chloride doped glassy materials are higher than those of the undoped ones and, at a particular dopant concentration, the following trend is observed. σ (–LiCl) ≥ σ (–NaCl) > σ (–MgCl 2) > σ (–PbCl 2) > σ (–CuCl 2) These results are supported by the experimental results of FT-IR spectral and thermal studies.

Structure and dynamics on superionic conducting phosphate glasses by neutron scattering

Neutron diffraction and inelastic scattering experiments have been performed on superionic conducting phosphate glasses, AgI–AgPO 3 and its undoped glass AgPO 3. In general, the static, elastic and dynamic structure factors S( Q), S( Q, ω=0), S( Q, ω), respectively, exhibit a prepeak at very low Q∼0.7 Å −1 related to the intermediate range order ∼10 Å, but not for the AgPO 3. The low-energy excitation, or Boson peak (BP), at around 2–3 meV appears in all undoped and doped glasses.The amplitude of the BP increases and the position shifts to lower energy with addition of AgI. The inelastic contribution can be expressed in terms of sound waves, Δ S( Q, ω) α Q 2 S( Q), which is consistent with an acoustic mode. The expansion of the phosphate network plays a dominant role on increasing the mobility of the Ag ions, the ionic conductivity, the prepeak and the BP intensities.

Superprotonic conducting phosphate glasses containing water

Fuel cells using H 2–O 2 offer the potential to minimize atmospheric pollution. Newly developed baria-phosphate glasses containing an appreciable amount of mobile hydrogen ions (protons) as well as molecular water exhibit super proton-conductivity. The new BaO–La 2O 3–Al 2O 3–P 2O 5 glasses exhibit high proton conductivities of 10 −2 S/cm at 200 °C and 10 −3 S/cm at 25 °C with a low activation energy of 0.17 eV. A H 2–O 2 fuel cell using this superprotonic glass electrolyte is operable at temperatures from 25 °C to 200 °C even under non-humidified conditions. The protons in oxide glasses have been often considered for a long time to be almost immobile. However, here we show that these superprotonic conductors of phosphate glasses are a good candidate material for viable electrolytes of fuel cells.

The Molecular Dynamics Study of Lithium Ion Conduction in Phosphate Glasses and the Role of Non-Bridging Oxygen

Molecular dynamics (MD) simulation of lithium phosphate (Li2O-P2O5) glasses with varying Li2O content has been carried out. Two different P-O distances corresponding to phosphorus coordination with bridging oxygen (BO) and non-bridging oxygen (NBO) were identified in the simulated glasses. NBO-BO interconversion or bond switching was noted, which results in a dynamic equilibration of the tetrahedral phosphate units (P-n, n = 1,3 indicates the number of bridging oxygen atoms in the coordination of phosphorus). The NBO-BO bond switching is mildly activated with an effective activation barrier of 0.03-0.05 eV. Lithium ion jumps do not appear to be strongly coupled to bond switching. But the number of Li+ ions coordinated to an optimum number of NBOs and the number of Li+ ions jumping out of their sites appear to be correlated. Detailed analysis was made of the dynamics of P-n species and new insights have been obtained regarding ion migration in network-modified phosphate glasses.

ChemInform Abstract: Protonic Conduction in Phosphate Glasses.

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Protonic Conduction in Phosphate Glasses

Protons in some alkaline earth metal‐phosphate glasses are much more mobile than monovalent ions such as Na+ and Ag+ ions under a dc electrical field. The O‐H bonding in those glasses that is weakened by the strong hydrogen bonding with neighboring nonbridging oxygen ions may cause the mobile protons.

ChemInform Abstract: Ionic Conduction in Phosphate Glasses

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ionic Conduction in Phosphate Glasses

Ionic conductivity in phosphate glasses has been known for almost 30 years. Recently these glasses have been shown to exhibit some of the highest ionic conductivities ever reported. In many cases, because of their ease of preparation, low melting points, strong glass‐forming character, and simple composition, phosphate glasses have been studied more than any other ionically conducting glasses. However, no single review has ever been made of these glasses with the purpose of correlating the apparent widely disparate values of conductivity that these glasses exhibit. In this review, the conductivities of phosphate glasses are examined considering new structural studies of them. A systematic comparison of the dependence of the conductivity on glass chemistry reveals that, similar to other glass families (silicates and borates for example), the conductivity maximizes when the cation environments in the glass are minimized in their charge density and maximized in their site proximity.