The Crystallization Behavior of a Na2O-GeO2-P2O5 Glass System: A (Micro)Structural, Electrical, and Dielectric Study.

Sodium-phosphate-based glass-ceramics (GCs) are promising materials for a wide range of applications, including solid-state sodium-ion batteries, microelectronic packaging substrates, and humidity sensors. This study investigated the impact of 24 h heat-treatments (HT) at varying temperatures on Na-Ge-P glass, with a focus on (micro)structural, electrical, and dielectric properties of prepared GCs. Various techniques such as powder X-ray diffraction (PXRD), infrared spectroscopy-attenuated total reflection (IR-ATR), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were employed. With the elevation of HT temperature, crystallinity progressively rose; at 450 °C, the microstructure retained amorphous traits featuring nanometric grains, whereas at 550 °C, HT resulted in fully crystallized structures characterized by square-shaped micron-scale grains of NaPO3. The insight into the evaluation of electrical and dielectric properties was provided by Solid-State Impedance Spectroscopy (SS-IS), revealing a strong correlation with the conditions of controlled crystallization and observed (micro)structure. Compared to the initial glass, which showed DC conductivity (σDC) on the order of magnitude 10-7 Ω-1 cm-1 at 393 K, the obtained GCs exhibited a lower σDC ranging from 10-8 to 10-10 Ω-1 cm-1. With the rise in HT temperature, σDC further decreased due to the crystallization of the NaPO3 phase, depleting the glass matrix of mobile Na+ ions. The prepared GCs showed improved dielectric parameters in comparison to the initial glass, with a noticeable increase in dielectric constant values (~20) followed by a decline in dielectric loss (~10-3) values as the HT temperatures rise. Particularly, the GC obtained at @450 stood out as the optimal sample, showcasing an elevated dielectric constant and low dielectric loss value, along with moderate ionic conductivity. This research uncovers the intricate relationship between heat-treatment conditions and material properties, emphasizing that controlled crystallization allows for precise modifications to microstructure and phase composition within the remaining glassy phase, ultimately facilitating the fine-tuning of material properties.

Electrical Transport in Iron Phosphate-Based Glass-(Ceramics): Insights into the Role of B2O3 and HfO2 from Model-Free Scaling Procedures.

In this work, we report the effect of the addition of modifiers and network formers on the polaronic transport in iron phosphate glasses (IPG) in two systems of HfO2-B2O3-Fe2O3-P2O5, to which up to 8 mol% boron and hafnium are added. The addition of oxides significantly changes the Fe2+/Fetotal ratio, thus directly affecting the polaron number density and consequently controlling DC conductivity trends for both series studied by impedance spectroscopy. Moreover, we found that short-range polaron dynamics are also under the influence of structural changes. Therefore, we have studied them in detail using model-free scaling procedures, Summerfield and Sidebottom scaling. An attempt to construct a super-master curve revealed that in addition to change in polaron number density, also the polaron hopping lengths change, and Sidebottom scaling yields a super-master curve. The spatial extent of the localized motion of polarons is correlated with polaron number density and two distinct regions are observed. A strong increase in the spatial extent of the polaron hopping jump could be related either to the structural changes due to the addition of HfO2 and B2O3 and their effects on the formation of polarons or to an inherent property of polaron transport in IP glasses with low polaron number density.

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.

High Electronically Conductive Tungsten Phosphate Glass-Ceramics.

High electronically conductive tungsten phosphate glass-ceramics have been prepared by the controlled crystallization of binary 60WO3-40P2O5 glass in the temperature range from 700 to 935 °C and for 1 to 24 h. The substantial increase in the conductivity for four orders of magnitude is a result of the formation of electronically conductive W2O3(PO4)2 and WO3 phases. At low crystallization temperature the dominant W2O3(PO4)2 phase is created, whereas at 935 °C for 24 h the formation of semiconducting WO3 crystallites of an average size of 80 nm enhances the conductivity to the highest value of 1.64 × 10-4 (Ω cm)-1 at 30 °C. The course of the crystallization and its impact on this exceptionally high electronic transport of binary tungsten phosphate glass-ceramics has been discussed in detail. Since such highly electronically conductive WO3-based glass-ceramics have a great potential as cathode/anode materials in solid state batteries and as electrocatalysts in fuel cells, it is of interest to provide a novel insight into the improvement of their electrical properties.

Polaronic Conductivity in Iron Phosphate Glasses Containing B2O3.

We report on the electrical properties of glasses with nominal composition xB2O3-(100-x)[40Fe2O3-60P2O5],x = 2-20, mol.%. The conduction transport in these glasses is polaronic and shows a strong dependence on Fe2O3 content and polaron number density. The changes in DC conductivity are found not to be directly related to B2O3, however structural changes induced by its addition impact frequency-dependent conductivity. All glasses obey Summerfield and Sidebottom procedures of scaling conductivity spectra indicating that the polaronic mechanism does not change with temperature. An attempt to produce a super-master curve revealed that shape of the conductivity dispersion is the same for glasses with up to 15.0 mol.% B2O3 but differs for glass with the highest B2O3 content. This result could be related to the presence of borate units in the glass network. Moreover, the spatial extent of localized polaron motions increases with the decrease of polaron number density, however, this increase shows a larger slope than for previously reported iron phosphate glasses most probably due to the influence of B2O3 on glass structure and formation of polarons. While Summerfield scaling procedure fails, Sidebottom scaling yields a super-master curve, which indicates that polaronic hopping lengths also change with changing polaron number density in these glasses.

Supramolecular ionogels prepared with bis(amino alcohol)oxamides as gelators: ionic transport and mechanical properties.

Supramolecular ionogels composed of an ionic liquid (IL) immobilized in a network of self-assembled low-molecular weight molecules have been attracting considerable interest due to their applicability as smart electrolytes for various electrochemical applications. Despite considerable scientific effort in this field, the design of a mechanically and thermally stable yet highly conductive supramolecular ionogels still remains a challenge. In this article, we report on a series of novel ionogels of three ILs containing different cations (imidazolium/pyrrolidinium) and anions (tetrafluoroborate/bis(trifluoromethylsulfonyl)imide) prepared using (S,S)-bis(amino alcohol)oxamides as gelators. The gelation behaviour of the oxamide compound depends strongly on the structural features of amino alcohol substituents. Among them, (S,S)-bis(valinol)oxamide (capable of gelling all three ILs) and (S,S)-bis(phenylalaninol)oxamide (capable of gelling ILs based on bis(trifluoromethylsulfonyl)imide with a concentration as low as ≈0.2 wt%) are highly efficient. All investigated supramolecular ionogels retain the high ionic conductivity and ion diffusion coefficients of their parent IL, even for high gelator concentrations. Further, at low temperatures we observe an enhancement of the ionic conductivity in ionogels of (i) 1-butyl-3-methylimidazolium tetrafluoroborate which can be attributed to specific interactions between ionic species and gelator molecules and (ii) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide due to inhibited crystallization. In contrast to ionic transport, mechanical strength of the ionogels shows a wider variation depending on the type and concentration of the oxamide gelator. Among all the ionogels, that of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide prepared with 1 wt% (S,S)-bis(phenylalaninol)oxamide exhibits the best performance: optical transparency, stability over a wide temperature range, high conductivity and high mechanical strength. The results presented here reveal the versatile nature of bis(amino alcohol)oxamides as gelators and their high potential for preparing functionalized IL-based materials.

Correction: Supramolecular ionogels prepared with bis(amino alcohol)oxamides as gelators: ionic transport and mechanical properties.

[This corrects the article DOI: 10.1039/D0RA01249A.].

The Effects of Silica on the Properties of Vitreous Enamels.

Ground coat enamels for low carbon steel that contain silica as a mill addition have been developed to study the changes of their properties. Acid-resistant commercial enamel where silica addition was varied from 0 to 10.0 wt % was used for this investigation. The effects of the addition on the corrosion resistance, thermal properties, electrical properties, and mechanical adherence of the enamel to low carbon steel were studied. The corrosion resistance of the steel enameled coupons was tested using a salt spray (fog) apparatus for time periods reaching 168 h at room temperature. It was found that, although the density was not affected, the adherence decreased with an increase in silica content. As expected, the silica addition decreased the coefficient of thermal expansion, which is directly related to the increasing stress between the glass and steel in accordance with the adherence results. A mill addition of 7.5 wt% of silica to the samples was sufficient to obtain adequate enamel adherence and good corrosion resistance. Furthermore, the addition of silica influenced the electrical conductivity and dielectric permittivity measurements at room temperature and the conductivity measured in a wide frequency range (1 Hz⁻1 MHz). The dielectric permittivity measured at 1 MHz showed decrease after the addition of up to 7.5 wt% of silica.

Polaronic transport in iron phosphate glasses containing HfO2 and CeO2.

The electrical and dielectric properties of three series of glasses, xHfO2-(40 - x)Fe2O3-60P2O5, 0 ≤ x ≤ 8 mol%, xCeO2-(40 - x)Fe2O3-60P2O5, 0 ≤ x ≤ 8 mol%, and xHfO2-(38 - x)Fe2O3-2B2O3-60P2O5 2 ≤ x ≤ 6 mol%, have been investigated by impedance spectroscopy over a wide frequency and temperature range. As expected, these glasses exhibit polaronic conductivity which strongly depends on the fraction of ferrous ions, Fe2+/Fetot. Following a detailed discussion on the DC conductivity, we use the MIGRATION concept to model their conductivity spectra. It is found that in each series of glasses, the shape of the conductivity isotherms remains the same indicating that the time-temperature superposition principle is satisfied and that the mechanism of conductivity is the same. Returning to a model-free scaling procedure, namely Summerfield scaling, it is found that while conductivity isotherms for each composition yield a master curve, we need to suitably shift individual master curves on the frequency axis to generate a super-master curve. We examine the dependence of the DC conductivity and the shift factors on the number density of charge carriers. Next, using the fact that the dielectric strength of relaxation for each isotherm is well-defined in these systems, we scale the conductivity isotherms using the Sidebottom scaling procedure. This procedure yields a super-master curve, implying that length scales for polaronic transport also change with composition. Further, using the scaling features of permittivity spectra, we extract in a straightforward way the characteristic spatial extent of localized hopping of polarons and find that it decreases with increasing number density of charge carriers. The magnitude of these values obtained from permittivity spectra lies in the same range as those for the polaron radius calculated using the equation proposed by Bogomolov and Mirilin.

Impedance changes during setting of amorphous calcium phosphate composites.

OBJECTIVES: To investigate the electrical properties of experimental light-curable composite materials based on amorphous calcium phosphate (ACP) with the admixture of silanized barium glass and silica fillers. METHODS: Short-term setting was investigated by impedance measurements at a frequency of 1kHz, while for the long-term setting the impedance spectra were measured consecutively over a frequency range of 0.05Hz to 1MHz for 24h. The analysis of electrical resistivity changes during curing allowed the extraction of relevant kinetic parameters. The impedance results were correlated to the degree of conversion assessed by Raman spectroscopy, water content determined by gravimetry, light transmittance measured by CCD spectrometer and microstructural features observed by scanning electron microscopy. RESULTS: ACP-based composites have shown higher immediate degree of conversion and less post-cure polymerization than the control composites, but lower polymerization rate. The polymerization rate assessed by impedance measurements correlated well with the light transmittance. The differences in the electrical conductivity values observed among the materials were correlated to the amount of water introduced into composites by the ACP filler. High correlation was found between the degree of conversion and electrical resistivity. Equivalent circuit modeling revealed two electrical contributions for the ACP-based composites and a single contribution for the control composites. SIGNIFICANCE: The impedance spectroscopy has proven a valuable method for gaining insight into various features of ACP-based composites. Better understanding of the properties of ACP-based composites should further the development of these promising bioactive materials.

Lithium-Ion Mobility in Quaternary Boro-Germano-Phosphate Glasses.

Effect of the structural changes, electrical conductivity, and dielectric properties on the addition of a third glass-former, GeO2, to the borophosphate glasses, 40Li2O-10B2O3-(50 - x)P2O5-xGeO2, x = 0-25 mol %, has been studied. Introduction of GeO2 causes the structural modifications in the glass network, which results in a continuous increase in electrical conductivity. Glasses with low GeO2 content, up to 10 mol %, show a rapid increase in dc conductivity as a result of the interlinkage of slightly depolymerized phosphate chains and negatively charged [GeO4](-) units, which enhances the migration of Li(+) ions. The Li(+) ions compensate these delocalized charges connecting both phosphate and germanium units, which results in reduction of both bond effectiveness and binding energy of Li(+) ions and therefore enables their hop to the next charge-compensating site. For higher GeO2 content, the dc conductivity increases slightly, tending to approach a maximum in Li(+) ion mobility caused by the incorporation of GeO2 units into phosphate network combined with conversion of GeO4 to GeO6 units. The strong cross-linkage of germanium and phosphate units creates heteroatomic P-O-Ge bonds responsible for more effectively trapped Li(+) ions. A close correspondence between dielectric and conductivity parameters at high frequencies indicates that the increase in conductivity indeed is controlled by the modification of structure as a function of GeO2 addition.

Supramolecular Ionic-Liquid Gels with High Ionic Conductivity.

Supramolecular ionogels were prepared by the gelation of room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4 ]) with (S,S)-bis(leucinol)oxalamide. Remarkably, the ionic conductivity of solutions and ionogels with low gelator concentrations is higher than that of neat [BMIm][BF4 ]. On the basis of molecular dynamics simulations and quantum mechanical calculations, the origin of this phenomenon is attributed to the higher affinity of gelator molecules towards [BF4 ](-) ions, which reduces the electrostatic attraction between [BMIm](+) and [BF4 ](-) and thus increases their mobility. With increasing gelator concentration, the ionic conductivity decreases due to the formation of a denser gelator matrix, which hinders the pathways for ionic transport. However, even for very dense ionogels, this decrease is less than one order of magnitude relative to neat [BMIm][BF4 ], and thus they can be classified as highly conductive materials with strong potential for application as functional electrolytes.

Electrical mobility of silver ion in Ag2O-B2O3-P2O5-TeO2 glasses.

The effect of adding TeO(2) into (100 - x)[0.5Ag(2)O - 0.1B(2)O(3) - 0.4P(2)O(5)] - xTeO(2), with 0-80 mol % TeO(2) glass, on the structural changes and electrical properties has been investigated. DSC and thermodilatomery were used to study their thermal behavior, structure was studied by Raman spectroscopy, and electrical properties have been studied by impedance spectroscopy over a wide temperature and frequency range. The introduction of TeO(2) as a third glass former to the glass network causes the structural transformation from TeO(3) (tp) to TeO(4) (tbp) which contributes to the changes in conductivity. The glasses with low TeO(2) content show only a slow decrease in dc conductivity with addition of TeO(2) due to the increase of the number of nonbridging oxygens, which increases the mobility of Ag(+) ions. The steep decrease in conductivity for glasses containing more than 40 mol % TeO(2) is a result of decrease of the Ag(2)O content and stronger cross-linkage in glass network through the formation of more Te-(eq)O(ax)-Te bonds in TeO(4) tbp units. The glasses obey ac conductivity scaling with respect to temperature, implying that the dynamic process is not temperature dependent. On the other hand, the scaling of the spectra for different glass compositions showed the deviations from the Summerfield scaling because of the local structural disorder which occurs as a result of the structural modifications in the tellurite glass network.