Charge Compensation in Sodium Borophosphate Glasses Studied by B-11{Na-23} and P-31{Na-23} Rotational Echo Double Resonance Spectroscopy

Autor(es)

Funke, Lena Marie ; Eckert, Hellmut

• Tipo de documento: Artigo Científico
• Fonte: Journal of Physical Chemistry C; v. 120, n. 6, p. 10-pg., 2016-02-18.

Resumo

Network former-network modifier interactions in three sodium borophosphate glasses have been probed by B-11{Na-23} and P-31{Na-23} rotational echo double resonance (REDOR) experiments. For the compositions chosen essentially all of the boron atoms in these glasses are four-coordinated and, thus, of formally anionic character, whereas the majority of the phosphorus species are of the (nominally charge-neutral) P-(3) type. Despite this fact, the dipolar second moments M-2(B-11{Na-23}) and M-2(P-31{Na-23}) extracted from these REDOR data indicate that the sodium cations interact significantly more strongly with the phosphate than with the borate species. As a matter of fact, the distance sums Sigma r(P-Na)(-6) calculated from these second moments are close to those measured in sodium ultraphosphate glasses with similar sodium concentrations, whereas the corresponding Sigma r(B-Na)(-6) values are significantly smaller than those measured in sodium borate glasses with comparable sodium concentrations. These results are corroborated by complementary Na-23{P-31} and Na-23{B-11} REDOR experiments. As supported by bond valence arguments, the formation of P-(3)-O-B-(4) linkages in borophosphate glasses results in a charge displacement away from the four-coordinated boron atoms toward the nonbridging oxygen atoms on the P-(3) units. These charge dispersal effects result in shallower Coulomb traps, thereby facilitating ionic mobility. (AU)

• Processo FAPESP: 13/07793-6 - CEPIV - Centro de Ensino, Pesquisa e Inovação em Vidros
• Beneficiário: Edgar Dutra Zanotto
• Modalidade de apoio: Auxílio à Pesquisa - Centros de Pesquisa, Inovação e Difusão - CEPIDs