Thermal, structural and crystallization study of Na2O–P2O5–Nb2O5 glasses

Exploring the Effect of V2O5 and Nb2O5 Content on the Structural, Thermal, and Electrical Characteristics of Sodium Phosphate Glasses and Glass–Ceramics

“…The dependence of T g on Nb 2 O 5 content in the 25V series is illustrated in Figure 1 c. Similar to V M , the T g trend follows a non-monotonic pattern, gradually decreasing until reaching a minimum for the 25V-20Nb glass, after which it begins to rise. These findings diverge from the anticipated thermal behaviour observed in similar glass systems, where T g typically increases nearly linearly with the addition of Nb 2 O 5 [ 27 , 29 , 30 , 31 , 32 , 33 , 34 ]. In contrast to the anticipated rise in T g with the incorporation of Nb 2 O 5 , the 25V series displays a minimum, and T g values exhibit only small changes upon the introduction of Nb 2 O 5 .…”

“…Non-monotonic trends observed in DC conductivity and activation energy were ascribed to the facilitating effect of Nb 2 O 5 on Na + ion transport, indicating the mixed glass former effect (MGFE). Furthermore, it has been shown that this series mirrors the behaviour demonstrated by the majority of A-P-Nb (A = Li [ 28 ], Na [ 29 , 30 , 31 , 32 , 33 ], K [ 34 ]) glass and glass–ceramic systems, where the addition of Nb 2 O 5 enhances both the thermal and electrical properties.…”

“…The density, ρ , of the samples demonstrates an increasing trend with the addition of Nb 2 O 5 ; see Figure 1 a. Interestingly, the molar volume, V M , exhibits a non-monotonic pattern as the content of Nb 2 O 5 increases, reaching its peak for glass at 25V-20Nb; see Figure 1 a. This observed behaviour is surprising, given that V M typically follows the opposite trend to that of ρ [ 29 , 30 , 31 , 32 , 33 , 34 ]. Changes in ρ and V M are commonly attributed to two factors: (i) the difference in molar masses—Nb 2 O 5 (265.81 g/mol) having a greater molar mass than P 2 O 5 (141.943 g/mol) and (ii) the difference in bond strengths—Nb–O bond being stronger (772 kJ/mol [ 35 ]) compared to the P–O bond (599 kJ/mol [ 35 ]).…”

“…Variations in T g typically arise from the same factors influencing ρ and V M , such as the replacement of weaker P–O bonds with stronger Nb–O bonds and the formation of a more condensed mixed niobate–phosphate (Nb-P) network, leading to an increase in T g in previously reported series [ 27 , 29 , 30 , 31 , 32 , 33 , 34 ]. However, the non-monotonic trend in T g within the 25V series indicates the unfavourable influence of Nb 2 O 5 on T g .…”

“…The effect of the gradual substitution of P 2 O 5 with Nb 2 O 5 on the structural characteristics of the glass and glass–ceramic samples from the studied 25V series is investigated using two complementary vibrational spectroscopy techniques—Raman and attenuated total reflectance infrared (IR-ATR) spectroscopy. Figure 4 illustrates the changes in Raman and IR-ATR spectra resulting from the incorporation of Nb 2 O 5 , and a detailed list of observed bands and their assignments, sourced from the literature data [ 29 , 30 , 31 , 32 , 33 , 34 , 36 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 ], can be found in Table S1 in the SM .…”