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Iron phosphate-based glasses (IPGs) belong to a family of electronically conducting amorphous materials. Due to the presence of transition metal (TM) ions, e.g. iron, in more than one valence state, the conduction mechanism of small polaron hopping (SPH) is present. These materials are of boundless scientific interest due to their potential application as electrode materials for batteries, electronic circuit elements, etc. Here, we report the effect of the addition of modifiers and network formers on the polaronic transport in binary IP glass. The electrical properties of two glass systems HfO2–B2O3–Fe2O3–P2O5 are studied in detail by Solid State Impedance Spectroscopy (SS-IS) over a wide range of frequencies and temperatures, revealing interesting features behind the polaronic transport. The addition of oxides significantly alters the Fe2+/Fetotal ratio, which directly affects the polaron number density and strongly controls the DC conductivity trends for both series. In addition, we found that short-range polaron dynamics are also under the influence of structural changes. Therefore, we studied them in detail using relatively simple but very informative model-free scaling procedures, namely Summerfield and Sidebottom scaling. Both procedures on the conductivity spectra confirmed the validity of the time-temperature superposition (TTS) principle for all glasses. An attempt to construct a super-master curve revealed that hopping lengths of the polarons also change, and Sidebottom scaling results in a super-master curve. In the next step, the spatial extent of the localized motion of the polarons is correlated with the polaron number density and two distinct regions with low and high polaron concentration glasses are confirmed. The transition between these regions is not only related to the polaron number density, but also to the combination of glass compositions and parameters that have an impact on the polaron motions. The relationship between the structural changes and conductivity mechanism is discussed in detail. The obtained results provide new valuable information about the resulting mixed glass network and its effect on the polaron formation and its dynamics.

Increased demand for stable and efficient electrolytes in batteries puts the focus of recent studies on the improvement of relatively low ionic conductivity in various families of oxide glasses containing alkali ions. A popular approach in achieving this goal is to add the second glass- forming oxide to the glass in order to induce structural changes which have a facilitating effect on the ionic transport. This phenomenon is well-known as the mixed glass-former effect. In this study, we show that a significant increase in ionic conductivity can be achieved by the replacement of glass-forming oxide P2O5 with WO3 and MoO3 which are not conventional glass-formers but conditional ones. For that purpose, four series of glasses 40Na2O–xMoO3–(60-x)P2O5, 40Na2O– xWO3–(60-x)P2O5, 40Li2O–xMoO3–(60-x)P2O5 and 40Li2O–xWO3–(60-x)P2O5 ; x=0-50 mol% were prepared by melt-quenching. The electrical characterization was performed by impedance spectroscopy in a wide frequency (0.01 Hz – 1 MHz) and temperature (-90 °C – 250 °C) range while the structural changes were followed by the 31P MAS-NMR and Raman spectroscopy. Comparing the phosphate glasses with different conducting ions, it was found that an increase in DC conductivity with the addition of transition metal oxides was more pronounced in lithium series, being five and four orders of magnitude for WO3 and MoO3, respectively. On the other hand, the enhancement of sodium ion conductivity was four orders of magnitude in the case of WO3 and three in the case of MoO3. Such difference is related to a smaller ionic radius and therefore higher mobility of lithium ions which can be more easily facilitated by the incorporation of tungsten and molybdenum units in the glass network. The trend in conductivity of sodium phosphate glasses was found to be non-linear, which is typical for the mixed glass former effect, exhibiting the maximal value at 30 mol% of MoO3 and 40 mol% of WO3. Similar compositional dependence was also found in the fraction of mixed molybdate/tungstate-phosphate units and the number of P-O-Mo/W linkages. These findings indicate that the fastest transport of sodium ions occurs at the maximally interconnected phosphate and molybdenum/tungsten units. On the other hand, lithium containing phosphate glasses did not show the typical effect of mixed glass formers on the electrical conductivity, even though the addition of WO3 and MoO3 produced similar network modification as in sodium containing glasses. In both series, the enhancement of ionic conductivity was found to be continuous for glasses containing up to 40 mol% of WO3 and MoO3 but retained for a higher fraction of these oxides. Here, similarly as in the sodium phosphate series, the formation of mixed molybdenum/tungsten-phosphate units strongly facilitates the transport of ions. However, at the highest amounts of WO3 and MoO3, smaller Li+ ions are less affected by the hindering nature of the glass network composed predominantly of molybdate and tungstate units, so the characteristic maximum in conductivity was not observed rather high values were retained.

Niobium phosphate glasses belong to an important class of oxide glasses and have functional properties thus making them attractive for various applications, such as waste form for radioactive immobilization, glass fibers, and optical lenses. Moreover, niobium oxide can be incorporated in combination with alkali oxides in a phosphate network in a wide composition range, which makes these glasses interesting for electrical applications and electrode/electrolyte materials for solid-state batteries. In this study, the structural and electrical properties of glasses with composition xNb2O5-(100-x)[0.45K2O-0.55P2O5], x=10-50 mol% are investigated by Raman (RS) and Impedance spectroscopy (IS). The glasses are synthesized by microwave heating. The melts are quenched in air by pouring into steel moulds and annealing at 773 K for 3 hours. Raman spectra show that the glass structure changes from predominantly orthophosphate (x≤20 mol%) to predominantly niobate (x=50 mol%) with increasing Nb2O5 content. In the glass network, the niobium forms NbO6 octahedra interlined with phosphate units (x=10 mol%), and is mutually interconnected via Nb-O-Nb bonds at higher Nb2O5 content. The DC conductivity decreases with increasing Nb2O5 content as the concentration of potassium ions (K+) decrease. Interestingly, this decrease is not linear suggesting that the glass structure strongly influences the transport of potassium ions. While glasses with predominant orthophosphate structure and those with predominant niobate glass network show a slight decrease in DC conductivity with increasing Nb2O5 content, the intermediate glass compositions exhibit a sharp drop in DC conductivity, which could be attributed to the hampering effect of the mixed niobate-phosphate network on the diffusion of potassium ions. Remarkably, a predominantly niobate glass network exhibits a rather facilitating effect which is evident not only in the trend of DC conductivity but also in the features of the frequency-dependent conductivity and the typical hopping lengths of the potassium ions. All glasses obey both Summerfield and Sidebottom scaling procedures of conductivity spectra indicating that the conductivity mechanism does not change with the temperature.

Fosfatna stakla koja sadrže alkalijske i prijelazne metalne okside intenzivno se istražuju posljednjih godina zbog jednostavne i ekonomične priprave te dobrih fizikalno-kemijskih svojstava. Ovi su materijali posebice interesantni za primjenu kao čvrsti elektroliti zbog mogućnosti dodatka relativno velike količine alkalijskih oksida (50 mol%). Ipak, dosadašnja su istraživanja pokazala da je ionska vodljivost niska i pri visokim koncentracijama ovih iona zbog njihove slabe pokretljivosti. U ovom smo istraživanju pokazali kako se pokretljivost alkalijskih iona u ovim materijalima može znatno povećati dodatkom WO3 i MoO3. Istraživanje je provedeno na dvije serije stakala pripravljene naglim hlađenjem taline: 40Na2O–xMoO3–(60-x)P2O5 i 40Na2O–xWO3–(60-x)P2O5 ; x = 0-50 mol%. Metodom impedancijske spektroskopije (IS) određena su električna svojstva stakala te se pokazalo kako ionska provodnost raste preko četiri reda veličine s dodatkom WO3, te oko tri reda veličine u slučaju MoO3. Osim toga, dobivena je i maksimalna vrijednost provodnosti pri 30 mol% MoO3 i 40 mol% WO3. Kako bi se dobio uvid u strukturne promjene nastale dodatkom navedenih oksida korištena je 31P MAS-NMR spektroskopija. Rezultati su pokazali kako ugradnja volframovih i molibdenovih poliedara u fosfatnu mrežu odnosno nastanak P-O-W/Mo veza prati isti trend ovisnosti o sastavu stakla kao i ionska provodnost. Navedeno upućuje da nastajanje miješanih volframovih/molibdenovih-fosfatnih jedinica ubrzava transport Na+ iona te značajno poboljšava ionsku vodljivost ovih materijala.

Niobium phosphate glasses belong to an important class of oxide glasses and have been investigated for a wide range of applications, such as the waste form for radioactive waste immobilization, glass fibers, and optical lenses, and electrode/electrolyte materials for solid-state batteries. In this study, structural and electrical properties of glasses with composition xNb2O5-(100-x)[0.45K2O-0.55P2O5], x=10-50 mol% were investigated by Raman and impedance spectroscopies. Glasses were synthesized by microwave heating of starting chemicals NH4H2PO4, Nb2O5, and KOH in a microwave oven with a nominal power of 1100 W for 30 min. The melts were quenched in the air by pouring them into steel molds and were annealed for 3 h at 773 K. Raman spectra reveal that the glass structure changes from predominantly orthophosphate (x≤20 mol%) to predominantly niobate (x=50 mol%) with increasing Nb2O5 content. In the glass network, niobium forms NbO6 octahedra which becomes mutually interconnected via Nb-O-Nb bonds at higher Nb2O5 content. The DC conductivity of glasses decreases with the increase in Nb2O5 due to a decrease in the concentration of potassium ions, however, this decrease is not linear indicating that glass structure strongly influences their mobility. While glasses with predominantly orthophosphate structure and those with predominantly niobate glass network exhibit a slight decrease in DC conductivity with increasing Nb2O5 content, the intermediate glass compositions exhibit a strong drop in DC conductivity which could be attributed to the hampering effect of the mixed niobate-phosphate network on the diffusion of potassium ions. Interestingly, a predominantly niobate glass network exhibits a rather facilitating effect which is evidenced not just in the trend of DC conductivity but also in the features of the frequency-dependent conductivity and typical hopping lengths of potassium ions.

Nowadays, sodium phosphate glasses are widely investigated as a cheap and easily accessible material for application in electrochemical devices. However, these glasses usually suffer from low electrical conductivity and a significant research effort has been undertaken to improve this property. In this study we show that the increase in sodium mobility can be achieved in a simple manner, by the addition of WO3 and MoO3 which depolymerize condense phosphate glass network and hence facilitate transport of Na+ ions thus improving overall electrical conductivity. The research was conducted on two glass series, 40Na2O–xMoO3–(60-x)P2O5 and 40Na2O–xWO3–(60- x)P2O5 ; x=0-50 mol% prepared by melt-quenching. The electrical properties were studied by impedance spectroscopy in a wide frequency (0.01 Hz – 1 MHz) and temperature (-90 °C – 250 °C) range. The results showed a significant increase in electrical conductivity with the addition of transition metal ions, being four orders of magnitude in the case of WO3 and three in the case of MoO3. However, the trend in conductivity was not linear, yet exhibited the maximal value at 30 mol% of MoO3 and 40 mol% of WO3 (Figure 1). In order to follow structural evolution, 31P MAS-NMR spectroscopy was used where the compositional dependence of P-O-Mo/W linkages exhibited a similar trend as the electrical conductivity. This led us to conclude that the maximally interconnected phosphate and molybdenum/tungsten units form a favourable environment for fast sodium ion transport in contrast to the predominantly phosphate or molybdenu/tungsten glass network. Furthermore, tungsten oxide was found to be more interconnected with the various P2O5 units inducing therefore a higher electrical conductivity of the Na2O–WO3–P2O5 glasses.

Glass-ceramics are advanced functional materials that contain crystalline phase(s) embedded in a glass matrix. Their electrical properties can be modified by tuning the nature and amount of phase(s) that crystallize in the glass upon the heat-treatment. This study shows how crystallization influences the mobility of electrons(polarons) and sodium ions in binary WO3- P2O5 and Na2O-WO3-P2O5 glasses, respectively. The parent 60WO3-40P2O5 and 40Na2O-50WO3-10P2O5 (in mol%) glasses were prepared by conventional melt-quenching technique and were subsequently heat-treated at temperatures above their glass transition temperature and at their crystallization temperature (700 °C, 800 °C and 935 °C for 60WO3-40P2O5 glass and 400 °C and 490 °C for 40Na2O-50WO3-10P2O5 glass) for various times (from 1 to 24 hours). The electrical properties of prepared glass-ceramics were investigated by impedance spectroscopy in a wide frequency (0.01 Hz – 1 MHz) and temperature (-30 °C – 250 °C) range while structural properties were evaluated by X-ray powder diffraction (XRPD) and SEM-EDS analysis. In the case of 60WO3-40P2O5 glass, heat-treatments from 700 °C to 935 °C induced evolution of structure from amorphous to the structures with dominant W2O3(PO4)2 and minor WO3 crystalline phases. The electrical conductivity of amorphous sample prepared at 700 °C decreased in comparison to the parent glass due to the rearrangement of the glass network upon heating which accompanies breaking of the bonds in the tungsten clusters which consequently impedes transport of polarons Nevertheless, with further increase in heat-treatment time and temperature a significant rise in conductivity was observed as a consequence of crystallization of conductive W2O3(PO4)2 and WO3 phases. The highest conductivity was obtained for glass-ceramic prepared at 935 °C for 24h where rapid electron transport occurs through WO3 crystallites. On the other hand, 40Na2O-50WO3-10P2O5 sample heat- treated at 400 °C remained amorphous with similar ionic conductivity as the parent glass, whereas treatment at 490 °C resulted in partially crystallized sample with slightly lower conductivity. Here, the glass-ceramic was found to contain Na2W2O7 crystallites embedded in amorphous glassy matrix. In the crystalline Na2W2O7 phase, sodium ions move between interstitial positions of corner-sharing WO6 octahedral and WO4 tetrahedral due to which their mobility is slower and hence overall ionic conductivity of the glass-ceramic lower. Therefore, in contrast to the electronically conductive binary tungsten- phosphate glass in which the crystallization produces a significant increase in conductivity, the crystallization processes in sodium tungsten- phosphate glass have a negative effect on the mobility of sodium ions causing a decrease in ionic conductivity in glass-ceramics.

Niobium phosphate glasses have functional properties which make them attractive for various fields of application, from optical and laser technology, nuclear waste immobilization to biomedicine. [1] Moreover, in combination with alkali oxides, niobium oxide can be incorporated in a phosphate network in a wide compositional range which makes these glasses interesting for electrical applications. In this study, glasses with composition xNb2O5-(100-x)[0.45K2O-0.55P2O5], x=10-50 mol%, were prepared by microwave heating and their ionic conductivity and structure were investigated by impedance and Raman spectroscopies. Raman spectra reveal that the glass structure changes from predominantly orthophosphate (x≤20 mol%) to predominantly niobate (x=50 mol%) with increasing Nb2O5 content. In the glass network, niobium forms NbO6 octahedra which, at higher Nb2O5 content, become mutually interconnected via Nb-O-Nb bonds. The changes of the electrical conductivity with composition suggest a strong influence of glass structure on the mobility of potassium ions. Glasses with predominantly orthophosphate structure and predominantly niobate glass network exhibit a slight decrease in DC conductivity with increasing Nb2O5 content, whereas intermediate glass compositions show a strong drop which could be attributed to the hampering effect of the mixed niobate-phosphate network on the diffusion of potassium ions. On the contrary, predominantly niobate glass network exhibits a rather facilitating influence which is evidenced not just by the trend of DC conductivity but also by the features of the frequency-dependent conductivity and typical hopping lengths of potassium ions.

Phosphate glasses containing transition metal oxides such as MoO3 and WO3 are well-known for their semiconducting nature with polaronic conduction mechanism. Also, these glasses can accommodate a relatively high amount of alkali and silver oxides which give rise to ionic conductivity. Such a large compositional and preparation variability enables tuning of the types and mechanisms of the electrical conduction and makes these materials attractive for application in modern electrochemical devices. In this contribution, we discuss various factors that influence electrical transport in these glasses from simple binary WO3/MoO3-P2O5 systems to complex ones containing variable amounts of alkali/silver oxides. Interestingly, WO3 and MoO3 can play very different roles in the electrical conduction in these materials. While polaronic conductivity in MoO3-P2O5 glasses depends strongly on the amount of MoO3 and fraction of molybdenum ions in different oxidation states, in phosphate glasses containing WO3 it is governed mainly by the features of the glass structure, in particular clustering of tungsten units which facilitates the transport of polarons. In combination with alkali oxides, WO3 and MoO3 can actively contribute to the electrical conductivity via polaronic transport, hence giving rise to the mixed ion-polaron conductivity. On the other hand, these oxides can influence the conductivity without introducing the polaronic conduction - by forming mixed phosphate–tungstate and phosphate–molybdate units in the glass network which facilitate the transport of alkali ions in a similar manner to in the classical mixed glass-former effect.

Iron phosphate-based glasses (IPG) belong to a family of electronically conducting amorphous materials. A small polaron hopping conduction mechanism is observed owing to the presence of transition metal ions, e.g. iron, in more than one valence state. These materials are of great scientific interest due to their potential application as electrode materials for batteries, electronic circuit elements, electrical switching devices, etc. Here, we report on the impact of the additional glass-forming oxide on the polaronic transport in binary IPG glasses. The electrical transport properties and correlation to glass structure in B2O3–Fe2O3–P2O5 system are studied by Solid-State Impedance Spectroscopy (SSIS) in a wide frequency and temperature range.[1] Electrical transport in these glasses shows a strong dependence on the polaron number density determined by the overall Fe2O3 content and the fraction of Fe2+ ions. While the analysis of DC conductivity and its temperature dependence gives important information on the long-range transport of charge carriers in glasses, features of the frequency-dependent conductivity provide insights into the processes of their localized motions. The DC conductivity trend is found to be unimpaired to the amount of gradually added second glass-former, B2O3. However, a detailed study of the scaling properties of the conductivity spectra reveals that structural changes induced by its addition up to 17.7 mol %, notably impact frequency-dependent conductivity. In this respect, we apply two relatively simple yet very insightful scaling procedures, namely Summerfield and Sidebottom scaling. Obtained results provide new valuable information on the influence of B2O3, as a second glass-former, and resulting mixed glass network, on the formation of polarons and their dynamics.

In recent years, sodium phosphate glasses have gained considerable interest as potential components of various electrochemical devices. Their chemistry makes them particularly interesting as a replacement for conventional and high cost lithium materials used in solid- state batteries. Although sodium glasses show lower electrical conductivity than lithium ones, the ionic transport can be greatly facilitated by the addition of another conventional or in our case conditional WO3/MoO3 glass-former (so-called mixed glass former effect, MGFE). In this study, we report enhancement of ionic conductivity as a result of compositional and structural changes occurring with the gradual replacement of P2O5 with WO3/MoO3 in 40Na2O– xMoO3–(60-x)P2O5 and 40Na2O–xWO3–(60-x)P2O5 ; x=0-50 mol% glass systems. The electrical properties were studied by impedance spectroscopy in a wide frequency (0.01 Hz – 1 MHz) and temperature (-90 °C – 250 °C) range while the structural features were evaluated by 31P MAS-NMR spectroscopy. From the frequency-independent part of the conductivity spectra, the values of DC conductivity, DC, at various temperatures and activation energy, EDC, for all glasses were determined. Interestingly, the results show non-linear dependence of DC conductivity with increase in WO3 and MoO3 content, with the highest value at 30 mol% of MoO3 and 40 mol% of WO3. The observed increase is more pronounced in tungsten containing glasses resulting in significantly higher electrical conductivity than molybdenum ones. 31P MAS NMR spectroscopy revealed that the changes in glass network i.e. formation of mixed phosphate- molybdate/tungstate units and number of P-O- Mo/W linkages are directly linked to the mobility of sodium ions. Precisely, the compositional dependence of P-O-Mo/W linkages follows similar compositional dependence as does the electrical conductivity, with the same position of maximal values at 30 and 40 mol% of MoO3 and WO3, respectively. Based on this, we assume that the maximally interconnected P2O5 and WO3/MoO3 units provide favourable structural environment for faster sodium transport than predominantly phosphate or predominantly molybdenum/tungsten network. Comparing the two glass series, a higher degree of interconnection with various phosphate units was also found in tungsten containing glasses exhibiting therefore higher electrical conductivity. In the next step, we investigated the frequency-dependent conductivity where the validity of Summerfield scaling for all glasses confirmed time-temperature superposition (TTS) and temperature invariant mechanism of ionic conductivity. More importantly, characteristic hopping length of sodium ions, evaluated from the crossover frequency between DC and AC conductivity, was found to be strongly correlated to the structural features, once again, reaching the highest value for maximally interconnected glass network (30 and 40 mol% of MoO3 and WO3, respectively). This confirmed that the formation of mixed units in our materials significantly enhances the dynamic of sodium ions on both microscopic and macroscopic level.

Niobium phosphate glasses belong to the important class of oxide glasses and have been investigated fora wide range of applications, such as the waste form for radioactive waste immobilization, glass fibers and optical lenses, electrodes, as potential solid electrolytes for batteries. In this study structural and electrical properties of glasses with composition xNb2O5-(100-x)[0.45K2O- 0.55P2O5], x=10-50 mol% were investigated by Raman and impedance spectroscopies. Glasses were synthesized by microwave heating of starting chemicals NH4H2PO4, Nb2O5, and KOH in a microwave oven with a nominal power of 1100 W for 30 min. The melt was quenched in the air by pouring it into steel molds and was annealed for 3 h at 773 K. From the Raman spectra, it can be observed that phosphate network gets progressively depolymerized as Nb2O5 content increases replacing the metaphosphate groups by octahedral [NbO6]7−. This indicates that niobium oxide acts as a conditional glass- former. The DC conductivity decreases with a decrease in K2O suggesting that it depends on the concentration of potassium ions. However, a non-linear dependence indicates that potassium mobility is also dependent on structural changes in the glass network i.e. stronger cross-linkage in the niobium rich glass hinders the dynamics/transport of K+ ions. All glasses obey both Summerfield and Sidebottom scaling procedures of conductivity spectra indicating that the conductivity mechanism does not change with the temperature.

Oxide glasses containing Li2O or Na2O in combination with transition metal oxide (TMO) have recently emerged as promising candidates for cathode materials in battery technologies. Such glasses exhibit mixed ion-polaron conductivity with the ionic contribution being dependent on the concentration and mobility of the alkali (Li+/Na+) ions whereas polaronic conductivity follows the small polaron hopping mechanism and depends on the amount of TMO and a relative fraction of TM ions in different valence states. In this study, we report the influence of WO3 and MoO3 on the transport of sodium ions in phosphate glasses. Two series of glasses of molar composition 40Na2O-xWO3-(60-x)P2O5 and 40Na2O-xMoO3-(60-x)P2O5, x = 0, 10, 20, 30, 40, 50 mol%, were prepared by melt quenching. Electrical properties of glasses were measured by impedance spectroscopy over a wide temperature and frequency range. Raman spectroscopy was used for structural characterization, whereas the fractions of tungsten and molybdenum ions in different valence states were determined by EPR spectroscopy. The DC electrical conductivity of glasses changes non-linearly as P2O5 is gradually replaced by WO3/MoO3 exhibiting maximum at 40 mol% WO3 (1.6 x 10-8 S/cm at 303 K) and 30 mol% MoO3 (2.2 x 10-9 S/cm at 303 K). Raman spectra reveal that with the addition of WO3/MoO3, octahedral WO6/MoO6 units enter the phosphate network, gradually depolymerize metaphosphate chains and form tungstate/molybdate network. We propose that the observed conductivity enhancement of approximately four orders of magnitude originates from the modification of glass structure which has a favourable effect on the mobility of sodium ions rather than the contribution of polaronic transfer between tungsten or molybdenum ions in different valence states. Indeed, EPR study revealed that the fraction of W5+/Wtot and Mo5+/Motot is less than 1% which suggest that the polaronic conductivity in these glasses is small. In conclusion, we show that the mixed-glass former effect can be extended to the glass systems where the conventional glass forming oxide (P2O5) is replaced by the conditional one (WO3/ MoO3).

In this study glasses of the composition (30- 0.5x)M2O-(30-0.5x)ZnO-40P2O5-xTMO (0≤x≤60 mol%) (M = Li, Ag ; TMO = WO3, MoO3) have been investigated. Due to containing both alkali and transition metal oxides, the nature of electrical transport in these glasses is ionic-polaronic. Ionic transport depends on the mobility and concentration of Li+ and Ag+, while polaronic transport depends on the concentration of small polarons. Mixed ion-polaron glasses have been thoroughly investigated for potential applications in solid state Li or Ag batteries as cathode materials. The goal of this investigation is to determine how the replacement of Li2O and Ag2O with WO3 and MoO3 in four glass series affects the glass structure and electrical properties. Raman spectroscopy was used for structural investigation, while electrical properties were determined by impedance spectroscopy. The results have shown that glasses with high Ag2O content have much higher electrical conductivity then their Li2O counterparts of the same composition. The addition of WO3 to the glasses in both series of zinc phosphate glasses causes a drop in electrical conductivity until a minimum (at 20 mol% for Li series and 30-40 mol% of Ag series). Further addition of WO3 increases the electrical conductivity for several orders of magnitude. On the other hand, MoO3 series show different results. In the case of Li series the electrical conductivity is nearly constant up to 50 mol% of added MoO3, while in the same compositional range of Ag series the conductivity is almost linearly decreasing. Further addition of MoO3 shows a slight increase of conductivity due to pure polaronic nature of the glass.

The constant rise of special requirements for energy storage systems has resulted in a rapid increase in the research of materials suitable for solid electrolytes and electrodes in all- solid-state ion batteries. In demand for safer, more efficient and less costly solutions, the question arises whether more naturally abundant sodium can replace lithium in ion batteries [1, 2]. In this study, two sodium ion conducting glass series are investigated: 40Na2O–(60-x)P2O5– xGeO2 and 40Na2O–10B2O3–(50-x)P2O5–xGeO2, x=0– 30 mol% in order to verify the mixed glass former effect (MGFE). Glass former exchange resulted in the significant electrical conductivity enhancement for both systems. Such behaviour is related to the increased mobility of Na+ ions, due to the depolymerization of the (boro)phosphate network and the emergence of easily conductive pathways after germanate incorporation and formation of different mixed Ge/B/P structural units. With the help of 1D/2D MAS NMR techniques, we are able to determine and quantify structural units formed in the network and gain insight into local environment and links between these units, which is crucial for determining the sodium ion transport mechanism. For better understanding of ionic transport in phosphate glasses, these results are compared to the study of 40Na2O–(60-x)P2O5–xMoO3/WO3, x=0–50 mol% glasses. In these systems, the ionic conductivity also increases significantly, as P2O5 is replaced by MoO3/WO3 (conditional network formers) implying that the mixture of phosphate and molybdate/tungstate units in glass network strongly facilitates transport of Na+ ions similarly as in classical MGFE. The ability to adjust the electrical properties of these MGFE systems by simple compositional changes and structure tuning is a very useful feature for their specific use.

A deep understanding of electrical transport in mixed conductive glasses is necessary for the development of these materials as cathodes in battery technologies. In this study, we report on the dynamics of polarons and ions in six glass series of composition WO3/MoO3-Li2O/Na2O/Ag2O-ZnO-P2O5 by examining their frequency-dependent conductivity using simple model-free scaling procedures proposed by Summerfield and Sidebottom. The validity of Sidebottom scaling for each glass confirms that the time-temperature superposition principle is satisfied implying that the basic conduction mechanism for individual glass does not change with temperature. However, Summerfield scaling is not valid for all glasses. Deviation observed for purely ionic Li2O glass and mixed Li2O-WO3/MoO3 glasses where Li+ conductivity dominates, originates from the specific interaction of Li+ ions with the local glass network. In addition, the deviation is also observed for particular WO3-based glasses in which the contribution of ionic conductivityis comparable to polaronic one. The cause of this phenomenon lies in the significant amount of both types of charge carriers and their different thermally activated mobility. We show how very fine differences in conductivity spectra, deduced solely from the experimental data, contain valuable insights into the dynamics of mixed ionpolaron transport.

Glass-ceramics based on 5M2O-5ZnO-40P2O5-50WO3 (in mol%, M = Li, Na, Ag) glasses were prepared by heat- treatment of the samples in the form of bulk and powder pellets at 725 and 800 ˚C for 6 hours. Structure and morphology of prepared glass-ceramics were studied by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM), while electrical properties were investigated using impedance spectroscopy. PXRD diffractograms show that two polymorphs of W2O3(PO4)2, rhombic and monoclinic, formed during crystallization in bulk samples prepared at 725 and 800 ˚C and pelleted samples prepared at 725 ˚C. However, diffractograms of pelleted samples heated at 800 ˚C show a distinct lack of diffraction peaks of rhombic polymorph. Furthermore, SEM and EDS have confirmed that the degree of crystallization increases with increasing temperature. Values of DC conductivity of measured glass-ceramics are similar to their parent glasses. This result indicates that crystallization does not impede polaronic transport in these glass-ceramics, thus producing conductive and hardy materials.

Impedance spectroscopy (IS) – a popular tool for analysis of electrical properties allows detailed investigation of composite materials like glass- ceramics. Notably, it enables the analysis of electrical response of every component within the composite. In this work IS is used for detailed analysis of complex mixed ion-polaron glass-ceramics. Glass-ceramics, Li50W@600 and Li50W@800, were prepared by heat- treatment of the starting bulk 5Li2O-5ZnO- 40P2O5-50WO3 (in mol%) glass at 600 ˚C and 800 ˚C for 6 hours. Analysis of IS results provided a detailed insight into changes of DC conductivity and relaxation processes based on the of Zʺ(ω) and Mʺ(ω) spectra in a wide frequency (0.01 Hz – 106 Hz) and temperature (303 K – 513 K) range. Structure and morphology of prepared materials were studied by powder X- ray diffraction (PXRD) and scanning electron microscopy (SEM). PXRD diffractograms showed that after heat-treatment of starting glass, Li50W@600 remained amorphous, while Li50W@800 contained two polymorphs of W2O3(PO4)2, orthorhombic and monoclinic. This was in accord with SEM analysis which showed sporadically distributed dendritic crystallization on the surface of Li50W@600, while SEM of Li50W@800 confirmed massive crystallization with some residual amorphous phase. IS measurements revealed that DC conductivity values of prepared glass-ceramics and the parent glass are within the same order of magnitude which indicates that the formation of W2O3(PO4)2 polymorphs does not impede predominantly polaronic electrical transport. Further, Zʺ(ω) and Mʺ(ω) spectra of Li50W@600 show practically overlapped peaks suggesting a single bulk response. On the other hand, Li50W@800 spectra show three distinct maxima in Zʺ(ω) and one slightly broadened peak in Mʺ(ω) spectrum. This indicates four distinct processes contributing to the total electrical conductivity which are related to the glass matrix, both crystallized polymorphs and grain boundary.

The mixed-alkali effect (MAE) is nonlinear deviation of the ionic conductivity observed when one type of alkali cation is replaced by another at their constant total cation content. Various models try to describe this effect but a comprehensive understanding is still lacking. In this work, three series of mixed-alkali aluminophosphate glasses, xLi2O-(40-x)Na2O- 10Al2O3-50P2O5, xLi2O-(40-x)K2O- 10Al2O3-50P2O5 and xNa2O-(40-x)K2O-10Al2O3-50P2O5, x=0-40 mol%, are examined to clarify the influence of cation size mismatches on the extent of MAE. Electrical properties of glasses are studied by impedance spectroscopy (IS) in a wide frequency (0.01 Hz – 106 Hz) and temperature (303 K – 523 K) range, whereas Raman spectroscopy is used to obtain information about glass network and different cation environment. Raman spectra show two most intensive bands corresponding to vs(P-O-P) and vs(P-O2) stretching vibrations of bridging and non- bridging oxygen atom in metaphosphate glasses, respectively. Both of the vibrational frequencies are sensitive to the cation environment and are shifted to the lowest frequency with addition of smaller cations. In all three series of glasses the results of IS measurements revealed strong MAE with DC conductivity minimum at 0.5 of cation substitution. The change in extent of MAE corresponds to the difference in cation size mismatches ; that is a deepest minimum obtained for the Li-K series. A possible explanation of the effect assumes that ion hopping probability is reduced because of the mismatched energy sites adopted for more dissimilar cations.

Glass ionomer cements (GICs) belong to the class of restorative dental materials with a long and extensive usage. These materials consist of an aluminofluorosilicate glass powder and an aqueous polyacrylic acid and the cement formation arises from the acid–base reaction between components. Over the past decade, a significant effort has been undertaken to develop a hybrid material composed of the glass ionomer and an additional component, resins for example, to obtain the material with superior mechanical and esthetical properties. In such resin-modified glass ionomer (RM-GI), the setting process involves an acid–base reaction and polymerization (light and/or chemically activated). The key point in designing an advanced dental material with desired properties is a thorough understanding of the setting reaction. In this study, the setting process in the commercial GIC (Fuji IX Fast) and RM-GI (Fuji II LC) was investigated by dielectric spectroscopy and digital laser interferometry. The changes in the real and imaginary parts of the dielectric permittivity as well as dielectric loss tangent with time for Fuji IX Fast show several distinct regions which can be related to the different stages of the acid–base reaction. Interestingly, the first stage that lasts for approximately 12 minutes terminates with a sharp decrease in dielectric parameters which is most probably related to the instantaneous (micro)fracturing of the sample due to a rapid build–up of the shrinkage stress. On the contrary, evolution of the dielectric properties during the setting of Fuji II LC indicates fast light- activated polymerization in the initial stage (less than a minute) followed by the slow gradual change. This results from the competing nature of the acid–base reaction and light-activated polymerization. In general, these results demonstrate that the dielectric spectroscopy is a sensitive tool for monitoring the complex changes during the setting process in dental materials.

Cilj je ovog istraživanja ispitati utjecaj dodatka prijelaznih metalnih oksida, WO3 i MoO3, na strukturu i električna svojstva srebro cink fosfatnih stakala. Značajka električnog transporta stakala koja sadrže Ag2O i prijelazne metalne okside je ionsko-polaronska vodljivost (IPE). Zbog ionsko-polaronskog prijenosa naboja ova stakla pokazuju velike mogućnosti u primjeni kao katodni materijali za čvrste baterije. Ionska vodljivost ovisi o količini i mobilnosti Ag+ dok elektronska vodljivost slijedi mehanizam malog polarona koji ovisi o količini iona prijelaznih metala u nižem oksidacijskom stanju. Detaljan uvid u prijenos naboja u ionsko-polaronskim staklima uključuje istraživanja raznih međusobno povezanih parametara, poput interakcija iona i polarona, interakcije nositelja naboja i strukture, itd. Istraživana su stakla sastava xTMO-(30-0.5x)Ag2O- (30- 0.5x)ZnO-40P2O5 (TMO = WO3 i MoO3, 0≤x≤60%). Struktura stakala je određena Ramanskom spektroskopijom, dok su električna svojstva istraživana impedancijskom spektroskopijom (IS). Dodatkom WO3 i MoO3 u srebro cink fosfatna stakla dolazi do pada električne vodljivosti. Serija stakala u koju se dodaje WO3 početno pokazuje pad vodljivosti do minimuma na 30-40% množinskog udjela WO3, a daljnjim dodatkom WO3 nagli rast vodljivosti. Ovaj rezultat ukazuje na prijelaz iz dominantno ionske u dominantno polaronsku vodljivost. S druge strane, vodljivost MoO3 stakala, kako udio MoO3 raste, linearno pada do 50% množinskog udjela MoO3 dok neznatno poraste kod čistog polaronskog stakla koje ne sadrži Ag+ ione. Time se pokazuje da u MoO3 seriji stakala ionska vodljivost dominira gotovo cijelom serijom bez značajnog polaronskog doprinosa. U ovom istraživanju pokazalo se kako su promjene električnih svojstava, odnosno mehanizma prijenosa naboja, vrlo usko povezane sa strukturnim promjenama u staklima što će biti detaljno raspravljeno.

U ovom istraživanju istraživana su stakla sastava (30-0.5x)M2O-(30-0.5x)ZnO-40P2O5-xTMO (0≤x≤60%) (M = Li, Ag ; TMO = WO3, MoO3). Električni transport u staklima koja sadrže alkalijske i pseudoalkalijske okside i prijelazne metalne okside je ionsko- polaronski. Naime, ovisno o količini i mobilnosti Li+ odnosno Ag+ pokazuju ionsku vodljivost, dok polaronska vodljivosti ovisi o koncentraciji malog polarona odnosno udjelu iona prijelaznih metala u nižim oksidacijskim stanjima. Ova stakla se istražuju zbog moguće primjene u čvrstim Li ili Ag baterijama kao katodni materijali. Ovo istraživanje ima za cilj pokazati kako zamjena Li2O i Ag2O s WO3 i MoO3 u četiri serije stakala utječe na strukturu i električna svojstva. Da bi se dobio uvid u strukturu stakla korištena je Ramanska spektroskopija, dok se za istraživanja električnih svojstava stakla koristila impedancijska spektroskopija (IS). Stakla s visokim udjelima Ag2O pokazuju izrazito visoku električnu vodljivost u usporedbi sa stakalima s istim množinskim udjelom Li2O. U slučaju početnog dodatka WO3 u obje serije cink fosfatnih stakala dolazi do pada električne vodljivosti do minimuma (na 20% množinskog udjela WO3 za Li seriju stakala i 30- 40% množinskog udjela WO3 za Ag seriju stakala), dok daljnjim dodatkom WO3 vodljivost poraste za nekoliko redova veličine. S druge strane, električna vodljivost MoO3 stakala je u slučaju Li serije stakala gotovo konstantna do 50% množinskog udjela MoO3 dok u slučaju Ag serije stakala u istom području sastava vodljivost linearno pada. Nakon 50% množinskog udjela dodanog MoO3 primjećen je porast vodljivosti za čisto polaronsko staklo koje sadrži samo MoO3. U ovoj prezentaciji rezultata biti će naglasak na povezivanju promjena električne vodljivosti s promjenama strukture u ovisnosti o tipu oksida koji su prisutni u staklima, a prikazat će se i usporedni pregled električne vodljivosti.