Dicalcium Heptagermanate Ca2Ge7O16 Revised.

Redhammer, Günther; Roth, Georg; Amthauer, Georg

doi:10.1002/chin.200738007

Cited by 1 publication

(9 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These values show the same trend as n GeO , and notably, they both pass through a maximum, as a function of CaO content, something that has not been observed for cesium germanate glasses or indeed for any other binary alkali germanate glass series, although a similar phenomenon has been measured for thallium germanate glasses . As was the case for n GeO (Figure ), the values of r GeO for ambient pressure calcium germanate crystals ,,, are in excess of those measured for the glasses.…”

Section: Resultssupporting

confidence: 71%

“…On further CaO addition, n GeO remains approximately constant until it approaches the [GeO 6 ] model prediction at 35 mol % CaO, and then it drops sharply, in accord with that model, as the CaO content approaches 40 mol %. It is notable that the calcium germanate glasses have much lower n GeO values compared to those of the ambient pressure crystals, ,, all of which contain [GeO 4 ] tetrahedra and [GeO 6 ] octahedra but no [GeO 5 ] polyhedra. The glasses containing nominally 27, 30, 35, and 40 mol % CaO all have n GeO in excess of the [GeO 5 ] model, which implies that they contain [GeO 6 ] species, or else violate assumptions of the model and contain corner-sharing [GeO m ] (with m = 5, 6) units or [OGe 3 ] triclusters.…”

Section: Resultsmentioning

confidence: 99%

“…For the present study of calcium germanate glasses, r GeO was determined by the integration of rT N ( r ) (filled triangles), and yellow centers indicate compositions showing phase separation. Values for ambient-pressure crystalline calcium germanates ,, as well as vitreous cesium and thallium germanates and crystalline Cs 6 Ge 3 O 9 and Tl 8 Ge 5 O 14 are shown for comparison.…”

Section: Resultsmentioning

confidence: 99%

“…Peak fitting to T X (r) was initially attempted using just one Ge−O peak and one Ca−O peak, as illustrated in Figure 9 for the 40CaO•60GeO 2 glass. The use of a single Ge−O peak was based on the lower spatial resolution in the X-ray case and led to Ge−O 70,74,75 and barium 124−127 germanates as well as vitreous cesium 28 and thallium 77 germanates are shown for comparison. The lines represent the charge avoidance models of Hannon et al 29 for the formation of higher Ge coordinations of five (solid) and six (dashed).…”

Section: Methodsmentioning

confidence: 99%

“…Dashed lines in the upper panel are guides to the eye. (Values for CaO–GeO 2 crystals ,, are shown as filled stars. )…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

The Germanate Anomaly in Alkaline Earth Germanate Glasses

et al. 2017

View full text Add to dashboard Cite

A report is given of the first detailed investigation of the relation of structure to the germanate anomaly in alkaline earth germanate glasses. Pulsed neutron diffraction and high-energy X-ray diffraction measurements on calcium germanate glasses (22 to 41 mol % CaO, roller-quenched) show that the average Ge–O coordination number, n GeO, and average bond length, r GeO, exhibit broad maxima at ∼28 mol % CaO. Maxima in the mass density, atom number density, and glass-transition temperature also occur at a similar composition and are characteristic of the germanate anomaly. The anomalies occur at a higher modifier oxide content for alkaline earth (Ae) germanate glasses than for alkali (A) germanate glasses, attributed to the higher bond strengths within Ae-O polyhedra compared to those in A-O polyhedra. Consequently, the stabilization of [GeO6] octahedra and/or bridges between higher-coordinated [GeO m ] units (m = 5, 6) is a feature of AeO–GeO2 glasses, in contrast to the existence of only [GeO4] tetrahedra and [GeO5] units proposed in alkali (Cs) germanate glasses. At high CaO content, n GeO behaves as in thallium germanate glasses because of the very similar metal–oxygen bond strengths within [CaO7] polyhedra and [TlO3] units. The composition dependence of the atom number density at low modifier content follows a common trend for Ca, Sr, and Ba germanate glasses because modifier cations fill germanate network cages. Our results show that the germanate anomaly for calcium germanate glasses is related to both a packing effect and a structural change in the germanate network; there is not a simple dichotomy whereby only one of these factors is of significance for the germanate anomaly.

show abstract