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Heat capacities of crystalline and glassy lithium metaphosphate up to the transition region

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Details

Original languageEnglish
Pages (from-to)401-407
Number of pages7
JournalJournal of Thermal Analysis and Calorimetry
Volume123
Issue number1
DOIs
Publication statusPublished - 2016
Publication typeA1 Journal article-refereed

Abstract

Heat capacity measurements have been conducted by means of DSC on both crystalline and glassy lithium metaphosphate, from room temperature up to the melting region. The heat capacity of the glass is slightly higher than that of the crystal. Contrary to the crystal, in the neighborhood of T g, C p increases rapidly by 10 J mol−1 K−1 conferring to this glass a “fragile character.” Nevertheless, the passage through T m does not show any discontinuity and the values of the glass and of the crystal are identical. The Debye model appears to be realistic to describe the glass heat capacity to temperature dependence. The Debye temperature and frequency were determined by minimizing the R p and χ 2 parameters of the C v fitting curve. From the calculation of the entropy of the liquid at T > T m, the excess entropy of the glass at T g was determined. Using the dependence of the glass transition on the heating rate, we calculated the values of the activation energy for structural relaxation (E relax) and of the lower limit of the glass transition temperature (T∘g) which is a thermodynamic parameter, contrary to T g which is a kinetic parameter.

Keywords

  • Crystal, Glass, Glass transition, Heat capacity

Publication forum classification

Field of science, Statistics Finland