Details

Autor(en) / Beteiligte

• Weber, H.-J.

Titel

Bond volumes in crystals and glasses and a study of the germanate anomaly

Ist Teil von

• Journal of non-crystalline solids, 1999-02, Vol.243 (2), p.220-232

Ort / Verlag

Amsterdam: Elsevier B.V

Erscheinungsjahr

1999

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The unit cell of a crystal is decomposed into partial volumes V b of its bonds. V b is described in terms of the bond length d and the coordination number N by V b =V 0+α ∗(d 3/N) . On the basis of structural data of about 170 binary and ternary compounds, including borates, silicates and germanates, it is demonstrated that V 0=0 and α ∗ comp =12.25 define compact structures. V 0≠0 is a signature of structures containing free volumes or voids. The universal character of α ∗ comp permits the determination of the free volume V 0 in alkali-germanate glasses and thereby a quantitative test of the idea that a change of the germanium coordination is the origin of the germanate anomaly. The test shows that the idea does not work since the pure transition from N Ge=4 to N Ge=6 changes the volume of the glass only by a marginal amount. It is suggested that a redistribution of void sizes which is accompanied by a negative deformation of the network is the leading mechanism which is responsible for the anomaly.