Anomalous properties of silica glass

Although Si02 is a typical inorganic glass, it is also atypical in many ways. Several properties of vitreous silica are known to vary anomalously at low temperatures. Anomaly in the low temperature specific heat is the most notable and well investigated. This is reflected in serious disagreement between Debye temperatures calculated from thermal and acoustic measurements. (thermal) and(elastic) are respectively given by (Anderson and Dienes, 1960), 

6iy values calculated from both thermal and elastic data show a dip in the region of 10 to 15 K, but their extrapolation to 0 K indicates that dj, (elastic) is 600 K compared to (thermal) of 450 K. This is attributed 

The behaviour of elastic moduli of vitreous silica is also anomalous. The Young s modulus seems to continuously increase in the region of 100 to 1000 K. This has been understood on the basis of the experimentally observed extremely low values of thermal expansivity of vitreous silica. The modulus, M, can be treated as a function of any two thermodynamic variables M = M V, T) ox M = M(P, T). The temperature dependence of the modulus can therefore be written as, 

Pure silica is perhaps the only single component glass which has a number of practical applications but the making of pure Si02 glass is very expensive because the working temperatures required for shaping pure 

Crystalline Si02 (quartz) under pressure is known to undergo phase transition to stishovite (Baur and Khan, 1997) in which Si is 6-coordinated. 6-coordinated Si forms in binary silicophosphate glasses as a consequence of its chemistry (see later). 

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