The free energy of formation of Mg2TiO4 (synthetic qandilite), an inverse spinel with configurational entropy
Date
2005
Authors
O'Neill, Hugh
Scott, Dean
Journal Title
Journal ISSN
Volume Title
Publisher
E. Schweizerbartsche Verlagsbuchhandlung
Abstract
Synthetic qandilite (Mg2TiO4) is an inverse spinel in which random mixing of Mg and Ti on the octahedral site should give rise to a configurational entropy of 11.5 J K-1 mol -1. The free energy of formation of Mg2TiO 4 has been determined from the location of the univariant reaction MgTiO3 + MgO = Mg2TiO 4 in pressure-temperature space between 0 and 20 kbar; together with literature data for MgTiO3 and MgO, the results give S(98K)0 = 111.2 ± 0.6 J K-1 mol-1 for Mg2TiO4. This entropy is only 7.6 ± 0.9 J K-1 mol-1 more than the calorimetrically determined value of 103.6 ± 0.7 J K-1 mol-1. The discrepancy implies either considerable short-range order of Mg and Ti in Mg2TiO4, or perhaps an error in the high-temperature heat-capacity data for MgTiO 3 caused by disordering in this substance.
Description
Keywords
Keywords: energy; phase equilibrium; spinel; thermodynamics Order-disorder; Phase equilibria; Spinel; Thermodynamic data
Citation
Collections
Source
European Journal of Mineralogy
Type
Journal article
Book Title
Entity type
Access Statement
License Rights
Restricted until
2037-12-31
Downloads
File
Description