Implementation of the extended Einstein and two-state liquid models for thermodynamic description of pure SiO2 at 1 atm

Thermodynamic description of pure SiO2 at 1 atm was developed for the whole temperature range including the crystalline, supercooled liquid and amorphous phases. Thermodynamic properties of the crystalline phases were assessed using an extended Einstein model. The thermodynamic modelling was based on the critically assessed experimental heat capacity and enthalpy increment data and on the data on phase transitions. The Planck-Einstein approach was used to evaluate the heat capacity data and obtain a more accurate value for the standard entropy at 298.15 K for alpha-quartz, alpha-cristobalite and amorphous \ liquid phases. The value for the standard entropy for the amorphous phase obtained just from the assessment of heat capacity data and did not include non-zero residual entropy at 0 K. The liquid and amorphous phases were thermodynamically described as one phase using the two-state liquid model. It was shown that Gibbs energy expression for amorphous silicon dioxide could be evaluated without inclusion of non-zero entropy at 0 K.