Structural Studies of Mixed Glass Former 0.35Na₂O + 0.65[xB₂O₃ + (1 – x)P₂O₅] Glasses by Raman and ¹¹B and ³¹P Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopies

Abstract

The mixed glass former (MGF) effect (MGFE) is defined as a nonlinear and nonadditive change in the ionic conductivity with changing glass former composition at constant modifier composition. In this study, sodium borophosphate 0.35Na2O + 0.65[xB2O3 + (1 -x)P2O5], 0 ≤ x≤ 1, glasses which have been shown to exhibit a positive MGFE have been prepared and examined using Raman and 11B and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Through examination of the short-range order (SRO) structures found in the ternary glasses, it was determined that the minority glass former, B for 0.1 ≤ x ≤ 0.7 and P for 0.7 ≤ x ≤ 0.9, is "overmodified" and contains more Na+ ions than would be expected from simple linear mixing of the binary sodium borate, x = 1, and sodium phosphate, x = 0, glasses, respectively. Changes in the intermediate range order (IRO) structures were suggested by changes in the NMR spectral chemical shifts and Raman spectra wavenumber shifts over the full composition range x in the Raman and MAS NMR spectra. The changes observed in the chemical shifts of 31P MAS NMR spectra with x are found to be too large to be caused solely by changing sodium modification of the phosphate SRO structural groups, and this indicates that internetwork bonding between phosphorus and boron through bridging oxygens (BOs), P-O-B, must be a major contributor to the IRO structure of these glasses. While not fully developed, a firstorder thermodynamic analysis based upon the Gibbs free energies of formation of the various SRO structural units in this system has been developed and can be used to account for the preferential formation of tetrahedral boron groups, B4, by the reaction of B3 with P2 groups to form B4 and P3 groups, respectively, where the superscript denotes the number of BOs on these units, in these glasses. This preference for B4 units appears to be a predominate cause of the changing modifier to glass former ratio with composition x in these ternary MGF glasses and appears to be associated with the large negative value of the Gibbs free energy of formation of this group. Disciplines Materials Science and Engineering | Physical Chemistry CommentsReprinted with permission from The Journal of Physical Chemistry B 117 (2013) P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Through examination of the short-range order (SRO) structures found in the ternary glasses, it was determined that the minority glass former, B for 0.1 ≤ x ≤ 0.7 and P for 0.7 ≤ x ≤ 0.9, is "overmodified" and contains more Na + ions than would be expected from simple linear mixing of the binary sodium borate, x = 1, and sodium phosphate, x = 0, glasses, respectively. Changes in the intermediate range order (IRO) structures were suggested by changes in the NMR spectral chemical shifts and Raman spectra wavenumber shifts over the full composition range x in the Raman and MAS NMR spectra. The changes observed in the chemical shifts of 31 P MAS NMR spectra with x are found to be too large to be ...

Mixed Network Former Effects in Oxide Glasses: Spectroscopic Studies in the System (M2O)1/3[(Ge2O4)x(P2O5)1–x]2/3

“…On the one hand the 31 P NMR data clearly indicate that the germanate network is partially modified for x ≥ 0.4, on the other hand, neither Raman spectroscopy nor XPS provide any clear evidence for the formation of nonbridging oxygen atoms associated with depolymerized Ge (3) or Ge (2) units, except for the x ≥ 0.8 samples. Thus, the conclusion appears inescapable that germanate modification proceeds (at least partially) by the formation of higher-coordinated germanium Ge (5) and/or Ge (6) units in this glass system. This conclusion is consistent with recent neutron diffraction data by Hoppe et al on gemanophosphate glasses with similar compositions.…”

“…Ge (5) and Ge (6) units (with bond valences of 0.8 and 0.67) may be stabilized by interaction with P (3) units (bond valence 1. 25), and this interaction may contribute to the preference for heteroatomic P−O−Ge linkages in this glass system, as it is found experimentally.…”

“…Figure 11 shows this plot for the KGeP{Yb} and NaGeP{Eu} glasses. Again, the concentrations attributed there to the concentrations of Ge (3) units actually comprise the total inventory of anionic Ge (3) , Ge (5) , and Ge (6) units. The results underline that the observed behavior is the same for both network modifier cations.…”

Ionic Conductivity of Mixed Glass Former 0.35Na2O + 0.65[xB2O3 + (1 – x)P2O5] Glasses

“…At x = 0.4, B 4 makes up 37% of the SRO structural units and at x = 0.5 B 4 makes up 40% of the SRO structural units according to our previously reported NMR data. 51 However, at x = 0.4 and 0.5, phosphorus units make up 60 and 50% of the SRO units. The NMR data indicate that the number of B P 4 is greater than the B B 4 until x = 0.4, after which B B 4 is the dominant boron tetrahedral unit.…”

Mixed network former effects in tellurite glass systems: Structure/property correlations in the system (Na2O)1/3[(2TeO2)x(B2O3)1−x]2/3

“…Advanced NMR methods, together with O-1s X-ray photoelectron spectroscopy have furnished important information regarding this issue in a number of boroncontaining glasses [11,[26][27][28][29][30][31][32][33]. For example, the strongly non-linear compositional dependences of glass transition temperatures and ionic conductivities observed in alkali borophosphate glasses could be explained satisfactorily on a structural basis, using 11 B and 31 P single and double resonance NMR techniques [28][29][30][31][32][33]. These glasses are characterized by a very exothermic interaction between the two different network formers, resulting in nearly maximized numbers of B-O-P linkages [30].…”