Journal of Physical Chemistry C;
JAN 26 2017.
Citações Web of Science:
New mixed network glasses along the composition line xB(2)O(3)-(30 - x)P2O5-70SiO(2) have been prepared and characterized in terms of their chemical composition, viscosity, and characteristic temperatures. The physical properties have been correlated with structural information, obtained from Raman spectroscopy and advanced B-11, Si-29, and P-31 single and double resonance solid state NMR studies. Both the macroscopic and structural properties show nonlinear changes as a function of composition, with maximal values of the viscometric glass transition temperature near 12-13 mol % B2O3. The structure of phosphorus-rich glasses is dominated by tetrahedral B(4) units linked to three to four phosphorus species and multiple phosphorus environments, including P-(3) (branching phosphate) groups linked to silicon, and P-(4) units forming B-O-P linkages as in boron phosphate, BPO4 (superscripts denote the number of bridging oxygen species). In the boron-rich region, the phosphorus species are exclusively present as P-(4) groups and the boron atoms present in excess of a B/P ratio of unity are present in the form of three-coordinated B-(3) units forming both B-O-B and B-O-Si linkages. While these results document a strong mutual affinity of the boron oxide and phosphorus oxide components, the species concentrations and numbers of B-O-P linkages fall consistently below those numbers expected from a clustering scenario maximizing the number of such connectivities, indicating the absence of macroscopic phase separation. Important differences relative to the previously studied system xAl(2)O(3)-(30 - x)P2O5-70SiO(2) are discussed. (AU)