The Germanate Anomaly: What do we know?

O K-edge XANES studies of alkali germanophosphate glasses

“…Similar results have been reported in alkali germanophosphate glasses where the addition of alkalis targets the phosphate network by converting existing Q 3 PO 4 tetrahedra into Q 2 and Q 1 PO 4 tetrahedra [6]. Raman spectra of these glasses have shown that at low to intermediate concentrations of P 2 O 5 (8:1, 6:1 and 4:1 GeO 2 to P 2 O 5 ratios), depolymerization of the phosphate network occurs with the initial addition of alkali oxide.…”

Local structure around Ge in lithium germanate glasses analyzed by AXS and EXAFS techniques

“…This phenomenon is well known as a germanate anomaly, and similar behaviors have also been observed in the density measurements for other alkali germanate glasses (Ivanov and Evstropiev, 1962;Murthy and Ip, 1964). Since the physical properties of glasses correlate closely with the atomic structure, several advanced analytical studies have been applied for elucidating the structural model for this interesting behavior (Henderson, 2007). One of the key structural mechanisms responsible for the germanate anomaly is the change in the coordination number of Ge with the addition of an alkali oxide (Verweij and Buster, 1979).…”

Abrupt boundaries of intermediate phases and space filling in oxide glasses

“…The broad global minimum in molar volumes near x ~18%, identified with the Germanate anomaly, has been attributed by some 13,14,22 to an aspect of local structure , i.e., Ge coordination number increase. On the other hand, Henderson 13 has suggested that the anomaly comes from growth of small (GeO) n rings, n = 3-and 4-member at the expense of larger ones, a feature of medium range structure. In Raman scattering one indeed observes the n = 3, 4 ring fraction to increase as x ~20%.…”