The mixed network former effect in glasses: solid state NMR and XPS structural studies of the glass system (Na2O)x(BPO4)1−x

Abstract

The structural organization of sodium borophosphate glasses with composition (Na(2)O)(x)(BPO(4))(1-x) (0.25 ≤x≤ 0.55) has been investigated by differential scanning calorimetry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), as well as single- and double resonance (11)B and (31)P magic-angle spinning (MAS) NMR. (11)B MAS-NMR data indicate the dominance of anionic four-coordinated boron units, and (31)P MAS NMR reveals the successive transformation of neutral P(3) into singly charged P(2) units and their further transformation into doubly charged P(1) units at high Na(2)O contents. The quantification of these units provides detailed insight into the competition of the network formers borate and phosphate for the network modifier oxide. At low modifier content (x < 0.35), the anionic species are almost exclusively borate (B(4)) units, whereas at higher sodium concentrations, large numbers of anionic phosphate (P(2) and P(1)) species are formed. O-1s XPS data provide a quantitative distinction between B-O-B, B-O-P, and P-O-P linkages as well as non-bridging oxygen atoms, and comparable numbers can be extracted from (11)B and (31)P MAS-NMR experiments. Both XPS as well as (31)P{(11)B} and (11)B{(31)P} rotational echo double resonance (REDOR) NMR results reveal strong interactions between the two network formers boron oxide and phosphorus oxide, resulting in a preferred formation of B-O-P linkages. For higher Na(2)O contents, however, the successive network modification diminishes this preference, resulting in close-to-statistical network connectivities. Compositional trends of T(g) in the Na(2)O-B(2)O(3)-P(2)O(5) glass forming system can be correlated with the overall network connectedness, expressed by the total number of bridging oxygen atoms per network former species. However, separate linear correlations are observed for different compositional lines, indicating also the relevance of the type of network former linkages present.

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

“…11 The x = 0.8 and 1.0 samples show weak bands at 737 and 867 cm −1 evidencing the presence of Ge (2) and Ge (3) units, (GeO 2 ) stretch;sym and (GeO) stretch;sym , respectively. The weakness of these bands along with the observation of P…”

“…and 1319 cm −1 that can be attributed to the (P−O−P) stretch;sym , (PO 2 ) stretch;(a)sym , and (PO) stretch;sym , respectively. 26 These bands reflect the expected presence of both P (2) and P ( . Older works suspect that Ge 6 or Ge 5 units cause a signal at around 670 cm −1 , 27 which has, however, been called into question in later works.…”

“…25 Figure 5 shows such double quantum filtered spectra, based on J-couplings detected via 31 P-1D refocused INADEQUATE spectroscopy. 31 The spectrum proves the absence of any P− O−P linkages in the glass with x = 0.8, where the phosphate units occur exclusively as P (2) 2Ge and P…”

“…In many cases the spectral resolution is insufficient for allowing unconstrained peak deconvolutions. This is understandable, as a total of nine signal contributions, namely from P (3) 0Ge , P (3) 1Ge , P (3) 2Ge , P (3) 3Ge , P (2) 0Ge , P (2) 1Ge , P (2) 2Ge , P…”

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

“…43 and did not find evidence for the formation of BPO 4 units in their glasses. For example, Rinke et al 44 showed that the Raman spectra of BPO 4 crystal has a strong peak at ∼490 cm −1 , weaker peaks at 1120 and 240 cm −1 , and finally minor peaks at 465 and 1080 cm −1 . In our Raman spectra presented and analyzed above, we do not see evidence of BPO 4 units as we do not see evidence of a peak at 240 cm −1…”