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This 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. [ABSTRACT FROM AUTHOR]

Bulk glasses of the series (100−x)[0.4Na2O-0.2Nb2O5-0.4P2O5]-xB2O3 with x = 0–48 mol% B2O3 were prepared by slow cooling in air. Their glass transition temperature increases within the range of 0–16 mol% B2O3, but further additions of B2O3 result in its decrease. Their structure was investigated by Raman, 11B, and 31P MAS NMR spectroscopy. The relative number of BO4 units decreases with increasing B2O3 content, while the number of BO3 units increases up to 59 % at x = 48. The upfield shift of a broad resonance peak in the 31P MAS NMR spectra is ascribed to an increasing connectedness of the structural network with increasing B2O3 content. Strong Raman band at 916–929 cm−1 shows on the presence of NbO6 octahedra in the structural network of these glasses. With the B2O3 addition, a decrease in DC conductivity is observed, which is attributed to the decrease in the concentration of Na+ ions. [ABSTRACT FROM AUTHOR]

Mixed ionic-polaronic transport has been investigated in two series of glasses containing Na2O and WO3/MoO3, namely xWO3-(30-0·5x)Na2O-(30-0·5x)ZnO-40P2O5 and xMoO3-(30-0·5x)Na2O-(30-0·5x)ZnO-40P2O5, 0=x=60 (mol%). The changes in the conduction mechanism with the systematic alternation of the glass composition have been analysed in correlation to the structural modifications and variations of molybdenum and tungsten in different oxidation states. Raman spectra revealed the clustering of WO6 units by the formation of W-O-W bonds in glasses with increasing WO3 content while the co-existence of MoO4 and MoO6 units is evidenced in glasses containing MoO3. In particular, the dominant molybdenum coordination in glasses with highest MoO3 content is four suggesting the absence of clustering of molybdate units. The DC conductivity of glasses with =20 mol% of WO3 and =30 mol% of MoO3 is almost identical due to the dominance of ionic conductivity. In this compositional region, the introduction of tungstate and molybdate units in the glass structure increases the mobility of sodium ions and compensates the decrease in sodium number density. The significant difference in conductivity is observed for glasses with higher WO3 and MoO3 content. While for glasses containing MoO3 the conductivity remains almost constant up to 50 mol% of MoO3, it constantly increases for almost six orders of magnitude for glasses with up to 60 mol% of WO3. The behaviour of DC conductivity for glasses containing MoO3 suggests the transition from ionic to polaronic conduction mechanisms which transport pathways are independent of each other. On the other hand, significantly higher conductivity of glasses with higher amounts of WO3 originates from a huge polaronic contribution, much larger than in a case of MoO3. Such a high conductivity is a consequence of the clustering of tungstate units which forms continuous W-O-W-O-W bridges which significantly facilitate polaronic transport. [ABSTRACT FROM AUTHOR]

Transformation of electrical transport from ionic to polaronic in glasses, which are a potential class of new cathode materials, has been investigated in four series containing WO3/MoO3 and Li+/Na+ ions, namely: xWO3-(30−0.5 x)Li2O-(30−0.5 x)ZnO-40P2O5, xWO3-(30−0.5 x)Na2O-(30.5 x)ZnO-40P2O5, xMoO3-(30−0.5 x)Li2O-(30−0.5 x)ZnO-40P2O5, and xMoO3-(30−0.5 x)Na2O-(30−0.5 x)ZnO-40P2O5, 0 ≤ x ≤ 60, (mol%). This study reports a detailed analysis of the role of structural modifications and its implications on the origin of electrical transport in these mixed ionic-polaron glasses. Raman spectra show the clustering of WO6 units by the formation of W-O-W bonds in glasses with high WO3 content while the coexistence of MoO4 and MoO6 units is evidenced in glasses containing MoO3 with no clustering of MoO6 octahedra. Consequently, DC conductivity of tungstate glasses with either Li+ or Na+ exhibits a transition from ionic to polaronic showing a minimum at about 20-30 mol% of WO3 as a result of ion-polaron interactions followed by a sharp increase for six orders of magnitude as WO3 content increases. The formation of WO6 clusters involved in W-O-W linkages for tungsten glasses plays a key role in significant increase in DC conductivity. On the other hand, DC conductivity is almost constant for glasses containing MoO3 suggesting an independent ionic and polaronic transport pathways for glasses containing 10-50 mol% of MoO3. [ABSTRACT FROM AUTHOR]

Glasses in the BaO-MoO 3 –P 2 O 5 ternary system were prepared, their basic physical properties measured and their structure studied by Raman and 31 P NMR spectroscopies. A modified glass-forming region in this system under slow cooling of the melt was determined. Four compositional series, namely (50-x/2)BaO-xMoO 3 -(50-x/2)P 2 O 5 (A), 50BaO-yMoO 3 -(50-y)P 2 O 5 (B), 20BaO-zMoO 3 -(80-z)P 2 O 5 (C) and (70-u)BaO-uMoO 3 -30P 2 O 5 (D) were chosen for a discussion on changes of the structure and properties of the studied glasses. The glass transition temperature revealed a maximum in series A at x = 40 mol% MoO 3 and in series C at z = 50 mol% MoO 3 , whereas monotonous increase of T g in the series B and monotonous decrease in the series D was observed. 31 P MAS NMR spectra of the glasses revealed depolymerization of the phosphate network, due to the incorporation of molybdate units, and isolated PO 4 groups were identified in glasses with high MoO 3 content. Fitting the NMR spectra provided compositional dependences of phosphate units Q n . On the Raman spectra of glasses with low MoO 3 content, a strong vibrational band at 940–944 cm − 1 , with a shoulder at ~ 910 cm − 1 , dominated the spectra, which was assigned to the vibration of terminal oxygen atoms in molybdate structural units (M O – and M O). In glasses with high MoO 3 content, a broad band at ~ 854 cm − 1 , ascribed to Mo O Mo bonds, showed on the formation of octahedral clusters composed of MoO 6 units in the structure of these glasses. [ABSTRACT FROM AUTHOR]

Study of the glass to crystal transformation was realized for two ternary compounds belonging to the glass-forming region of the BaO Nb 2 O 5 P 2 O 5 system: Ba 3 Nb 2 (PO 4 ) 4 O 2 with 16.66 mol% Nb 2 O 5 (glass composition 3BaO.1Nb 2 O 5 .2P 2 O 5 ) and BaNb 2 P 2 O 11 with 33.33 mol% Nb 2 O 5 (glass composition 1BaO.1Nb 2 O 5 .1P 2 O 5 ). Physico-chemical properties of the corresponding glasses and crystals were compared, as well as their Raman, 31 P and 93 Nb NMR spectra. The density of polycrystalline samples is higher by 0.24–0.25 g cm −3 than the density of the corresponding glasses. 31 P MAS NMR spectra show a close similarity of phosphorus environments in glasses and the corresponding crystalline samples. High-field (18.8T) NMR and 93 Nb decoupling were necessary to obtain enough resolution on 31 P NMR spectra to separate the 2 different short range environments of phosphorus atoms in Ba 3 Nb 2 (PO 4 ) 4 O 2 . Static 93 Nb NMR spectra showed the presence of distorted NbO 6 octahedra both in the 3BaO.1Nb 2 O 5 .2P 2 O 5 glass and the corresponding Ba 3 Nb 2 (PO 4 ) 4 O 2 crystals, while the presence of more symmetric NbO 6 octahedra was detected in the BaNb 2 P 2 O 11 compound, which is in accordance with the crystalline structures. Raman and NMR spectra showed similar short-range structural features in glasses and polycrystalline samples, whereas Raman spectra could detect some differences in the medium-range order of the BaO.Nb 2 O 5 .P 2 O 5 glass and the corresponding BaNb 2 P 2 O 11 crystal. [ABSTRACT FROM AUTHOR]

Phosphate glasses containing a high amount of niobium oxide exhibit non-linear optical properties which make them attractive for various optical devices. This contribution is devoted to the investigation of glasses of the series (100 − x)[0.5BaO–0.1B 2 O 3 –0.4P 2 O 5 ]–xNb 2 O 5 with x = 0–45 and 80[0.5BaO–yB 2 O 3 –(0.5 − y)P 2 O 5 ]–20Nb 2 O 5 with y = 0–0.25. The basic characteristic parameters of the prepared glasses were determined. The index of refraction of these glasses increases substantially with increasing Nb 2 O 5 content from 1.620 to 2.007 and the glass transition temperature increases within the range of 551–704 °C. The glass structure was investigated by 31 P, 11 B and 93 Nb NMR, and Raman spectroscopies. Raman spectra revealed that at low Nb 2 O 5 content a strong vibrational band of isolated NbO 6 octahedra dominates the spectra. New bands appear in the Raman spectra in the glasses with 30 mol% of Nb 2 O 5 that were assigned to vibrations of Nb–O–Nb bonds interconnecting NbO 6 octahedra. 11 B MAS NMR spectra reveal the dominant role of BO 4 units in the glass structure. 11 B MAS NMR spectra revealed that with increasing Nb 2 O 5 content new resonances of BO 4 units appear in the spectra due to the replacement of B–O–P bonds by B–O–Nb and B–O–B bonds. With an increasing Nb 2 O 5 content, part of the BO 4 units is also converted to BO 3 units. 93 Nb MAS NMR spectra primarily reflect changes in the length of Nb–O bonds in the NbO 6 octahedra manifested in a decreasing asymmetry of the octahedra with increasing Nb 2 O 5 content and the formation of niobate clusters. Niobo-borophosphate glasses reveal very high chemical durability as well as high glass transition temperatures due to the replacement of weaker P–O bonds with stronger Nb–O bonds. [ABSTRACT FROM AUTHOR]

Lead borophosphate glasses of the composition (100-x)[0·5PbO.0·2B2O3.0·3P2O5]. xMoO3 with 0-70 mol% MoO3 were prepared and studied. Thermal studies were carried out with DTA and dilatometry. The glass transition temperature in these glass series decreases steadily with increasing MoO3 content from 467 to 342°C for the range x=0-70 mol% MoO3. The glass structure was studied by 31P and 11B MAS NMR and by Raman spectroscopy. These studies were devoted to the investigation of changes in boron coordination and their dependence on the MoO3 content and the B2O3/P2O5 ratio. When the molybdenum oxide and boron oxide content is low, tetrahedral BO4 units prevail in the structural network. With higher B2O3 content, as well as with higher MoO3 content, trigonal BO3 groups are also formed. 11B MAS NMR spectra of BO4 units in the glasses with a low boron content reveal two symmetrical signals for BO4 units, ascribed to B(OP)3O and B(OP)2O2 units with B-O-P and B(4)-O-B(4) bonds. In the 11B spectra of glasses with a higher B2O3 or MoO3 content, the number of B(OP)3O units decreases, and some B(OP)O3 units appear as well. The formation of mixed BO4 units with B-O-P, B-O-Mo and B-O-B bonds results in several close resonances from which the relative proportion of borate structural units can be obtained. The effect of changing the B2O3/P2O5 ratio on the structure of lead borophosphate glasses modified with MoO3 is also discussed. [ABSTRACT FROM AUTHOR]

• Glass-forming region in the system K 2 O-Nb 2 O 5 -P 2 O 5 was determined. • Glass structure and properties were studied in three compositional series. • Phase separation and crystallization limit glass-forming region. • Clustering of niobate octahedra results in the formation of potassium niobate crystals. Glasses of the ternary system K 2 O-Nb 2 O 5 -P 2 O 5 were studied in three compositional series (60-x)K 2 O-xNb 2 O 5 -40P 2 O 5 (series A) with 10–40 mol% Nb 2 O 5 , 40K 2 O-yNb 2 O 5 -(60-y)P 2 O 5 (series B) with 10–30 mol% Nb 2 O 5 and zK 2 O-20Nb 2 O 5 -(80- z)P 2 O 5 (series C) with 20–50 mol% K 2 O. The basic physical parameters of glasses were also determined. Almost all the glasses were colourless, only two glasses with a higher Nb 2 O 5 content were blue coloured due to the presence of a small amount of Nb4+ ions. The glass transition temperature in the series A and B increases with increasing Nb 2 O 5 content, whereas in series C it increases only slightly. The highest value of 757 °C was found for the glass 20K 2 O-40Nb 2 O 5 -40P 2 O 5 from the A series. The refraction index only increases significantly in the glasses of the series A and B with increasing Nb 2 O 5 content; glass 20K 2 O-40Nb 2 O 5 -40P 2 O 5 from the series A had the highest value of 1.809 at 587.6 nm. The glass structure was evaluated from an analysis of their 31P MAS NMR and Raman spectra. The efficiency of Raman scattering by NbO 6 units is higher than that of PO 4 units, which results in the suppression of phosphate vibrational bands in the Raman spectra of glasses with a higher Nb 2 O 5 content. In the glasses with 30–40 mol% Nb 2 O 5, Raman spectra showed on the formation of chains Nb-O-Nb interconnecting NbO 6 octahedra and even on the formation of 3D niobate clusters. Samples containing less than 30 mol% P 2 O 5 revealed a tendency to form glass-crystalline materials containing potassium niobate crystals. Their crystalline structure was not identified, but according to their Raman spectra, they contain NbO 6 octahedra similar to those in KNbO 3. [ABSTRACT FROM AUTHOR]

Abstract: The structure of 50ZnO–10B2O3–40P2O5+xTiO2 glasses prepared by slow cooling (for x=0–24mol% TiO2) or by quenching (for x=28–64mol% TiO2) was studied by Raman, 31P and 11B MAS NMR spectroscopy. TiO2 incorporates into the glass structure, which results in a decrease in the molar volume and an increase in the glass transition temperature. According to Raman spectra Ti atoms form distorted TiO6 octahedra and their incorporation into the structural network results in the depolymerization of phosphate chains. 11B NMR spectra of the glasses with increasing TiO2 content show gradual changes from one symmetrical signal of B(OP)4 units to a broad complex signal which was separated into five signals ascribed to four different types of BO4 units and one BO3 unit. With increasing TiO2 content a part of boron atoms changes from tetrahedral BO4 to trigonal BO3 units, which is ascribed to the formation of TiO6 units in the glass structure. [Copyright &y& Elsevier]

• Glass-forming region in the system BaO-WO 3 -P 2 O 5 was determined. • High ionicity limits glass formation in BaO rich glasses. • Glass structure and properties were studied in five compositional series. • Possible coordination change of tungsten from WO 6 to WO 4 revealed by Raman spectra. • Clustering of tungstate octahedra depends on the BaO/P 2 O 5 ratio. The purpose of this work was to prepare and study new glasses from the system BaO-WO 3 –P 2 O 5 focusing on their basic physical properties and studying their structure by Raman and 31P NMR spectroscopies in five compositional glass series. The glass transition temperature increases in all compositional series with increasing WO 3 content. The 31P MAS NMR spectra of the glasses revealed depolymerization of the phosphate network. In the Raman spectra of glasses with a low WO 3 content, two strong vibrational bands at 885 and 945 cm−1 were assigned to the vibration of W O and W-O− bonds in tungstate structural units. In glasses with a high WO 3 content, a broad band at 820–841 cm−1, ascribed to W-O-W bonds, indicated the formation of clusters composed of WO 6 units. Raman spectra also revealed partial transformation of WO 6 units into WO 4 units in glasses with a low P 2 O 5 content. [ABSTRACT FROM AUTHOR]

Abstract This work presents a study on the structure, thermal behavior and properties of (100-x)[0.5Li 2 O-0.1B 2 O 3 -0.4P 2 O 5 ]-xTeO 2 glasses prepared within the concentration range of x = 0–80 mol% TeO 2. The structure of the glasses was studied with a combined Raman, 31P and 11B MAS NMR spectroscopy. 31P MAS NMR and Raman spectrum of the pure 50Li 2 O-10B 2 O 3 -40P 2 O 5 glass indicates the co-existence of Q2 and Q1 phosphate units in the glass structure. Raman spectra of TeO 2 containing glasses revealed that TeO 2 is incorporated in the structural network in the form of TeO 3 and TeO 4 (TeO 3+1) units. The ratio of TeO 4 /TeO 3 increases with rising TeO 2 content. Apart from the formation of P‒O‒Te and Te‒O‒Te bonds, the formation of B‒O‒Te bonds in the form of mixed tetrahedral units B(OP) 4-n (OTe) n also takes place as shown by 11B MAS NMR spectroscopy. The structural studies were correlated with the thermal behavior and physical properties of glasses (density, molar volume, chemical durability and refractive index). DSC studies showed that all glasses crystallize on heating within a temperature region of 400–550 °C and the surface nucleation mechanism prevails over the internal one. The crystallization temperature decreases with increasing TeO 2 content. The compounds formed by crystallization were LiPO 3 , Li 4 P 2 O 7 , BPO 4 and α-TeO 2. Glass transition temperature and dilatometric softening temperature, estimated from thermodilatometry curves, decrease with increasing TeO 2 content, whereas the thermal expansion coefficient increases. Graphical abstract The compositional dependences of glass transition temperature, T g , dilatometric softening temperature, T d , and thermal expansion coefficient, α , of the (100-x)[0.5Li 2 O-0.1B 2 O 3 -0.4P 2 O 5 ]-xTeO 2 glasses, obtained from dilatometric curves. fx1 Highlights • Structure of Li 2 O-B 2 O 3 -P 2 O 5 -TeO 2 glasses. • Raman, 31P and 11B spectroscopy. • Thermal behavior and physical properties of Li 2 O-B 2 O 3 -P 2 O 5 -TeO 2 glasses. • Relationships between structure, thermal behavior and physical properties. [ABSTRACT FROM AUTHOR]

The present investigation deals with the study of the structure, properties and thermal behaviour of Na 2 O–P 2 O 5 –Nb 2 O 5 glasses prepared in the compositional series 40 Na 2 O- (60-x) P 2 O 5 - x Nb 2 O 5 (x=0–40 ​mol% Nb 2 O 5). The modification of starting 40 Na 2 O– 60 P 2 O 5 glass by Nb 2 O 5 revealed changes both in the structure and properties. The glass density steeply increases with increasing Nb 2 O 5 content while the molar volume decreases. Parent sodium ultraphosphate glass was covered with a thin layer of partially hydrolysed glass in air. The chemical durability of Nb 2 O 5 containing glasses was high. The replacement of P 2 O 5 by Nb 2 O 5 resulted in a gradual increase in the refraction index as well as in an increase in glass transition temperature and dilatometric softening temperature. DSC measurements demonstrated that glasses crystallize under heating in the temperature range of 330–880°C. The lowest thermal stability was found for the glass containing 40 ​mol% Nb 2 O 5. The Raman and NMR spectra indicated that the structure of 40Na 2 O–60P 2 O 5 glass is formed mainly by Q2 and Q1 phosphate units interconnected by P–O–P bonds. The replacement of P 2 O 5 by Nb 2 O 5 leads to depolymerization and the partial transformation of Q2 units into Q1 units and finally to isolated Q0 units. Nb 2 O 5 forms in the glass structure NbO 6 octahedra. [Display omitted] • Structure of Na 2 O–P 2 O 5 –Nb 2 O 5. • Raman and 31P MAS spectroscopy. • Thermal behavior and physical properties of Na 2 O–P 2 O 5 –Nb 2 O 5 glasses. • Structure, thermal behavior and physical properties relationships. [ABSTRACT FROM AUTHOR]

This study investigates the influence of structural modifications induced by the introduction of Nb 2 O 5 on the thermal, (micro)structural, and electrical properties of quaternary system 35Na 2 O–10V 2 O 5 -(55– x)P 2 O 5 - x Nb 2 O 5 (x = 0–40 mol%). Non-monotonic trends in DC conductivity and activation energy are attributed to the facilitating effect of Nb 2 O 5 on the transport of Na + ions, confirming the mixed glass former effect. The results demonstrate that the electrical conductivity mechanism is purely ionic, with V 2 O 5 acting as both, glass modifier and network-former with vanadate units being in predominantly 4-fold coordination and without actively participating in the conduction process. Complementary Raman and IR-ATR spectroscopic studies in combination with solid-state impedance spectroscopy (SS-IS) reveal a strong correlation between structural and electrical properties indicating that the enhancement in conductivity is driven by the formation of mixed niobate-phosphate glass network. The increase in conductivity is followed by a gradual transition of glass structure from a predominantly phosphate glass network (x ≤ 10, Region I) into a mixed niobate-phosphate glass network (10 ≤ x ≤ 20, Region II). The conductivity increases by a factor of ∼4.5 within the series reaching the highest value of 3.29 × 10−10 Ω−1 cm−1 for Nb-20 glass. In the predominantly niobate network (x ≥ 25, Region III), the 3D clustering of NbO 6 octahedra hinders the transport of Na + ions. The scaling features of the conductivity spectra additionally confirm the ionic mechanism of electrical transport and provide insight into the local dynamics of Na+ ions. [Display omitted] [ABSTRACT FROM AUTHOR]

Phosphate glasses containing transition metal oxides such as MoO 3 and WO 3 are well-known for their semiconducting nature with polaronic conduction mechanism. These glasses can also 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 WO 3 /MoO 3 -P 2 O 5 systems to complex ones containing variable amounts of alkali/silver oxides. Interestingly, WO 3 and MoO 3 can have very different roles in the electrical conduction in these materials. While MoO 3 contributes weakly via polaronic transport in phosphate glasses, it strongly increases the mobility of alkali/silver ions by forming the mixed phosphate-molybdate network. On the other hand, the role of WO 3 depends on the glass composition; it can contribute either directly, by introducing significant polaronic conductivity, or indirectly, by facilitating the transport of alkali/silver ions. The former behaviour is related to the formation of clusters of tungsten units in the glass network which enable fast transport of polarons whereas the latter one originates from the facilitating effect of mixed phosphate-tungstate units on the dynamics of alkali ions. • WO 3 and MoO 3 can exhibit different influence on structural and transport properties of phosphate glasses. • Clustering of tungsten units in glass network facilitates polaronic conductivity. • Formation of mixed phosphate-molybdate and phosphate-tungstate units increases mobility of alkali ions. [ABSTRACT FROM AUTHOR]