Thermochemistry of phases in the system MgGa2O4-Mg2GeO4

✍ Scribed by Kurt Leinenweber; Alexandra Navrotsky

• Publisher: Springer-Verlag
• Year: 1989
• Tongue: English
• Weight: 603 KB
• Volume: 16
• Category: Article
• ISSN: 0342-1791
• DOI: 10.1007/bf00197018

✦ Synopsis

The enthalpies of solution in molten 2PbO. B203 of phases synthesized at one atmosphere in the system MgGa20,-Mg2GeO4 have been measured. A spinel solid solution, which is stable at 1400 ~ from the MgGa204 end-member to 27 mole percent MgzGeO4, shows endothermic heats of mixing of up to 10 kJ/mole at the solubility limit. The spinelloid phase, MgaGazGeOs, is energetically less stable than a mixture of terminal spinel solid solutions (0.73 MgGa204' 0.27 Mg2GeO4(sp) + MgzGeOg(sp)), by 3.63_+ 3.64 kJ/mole. This indicates that the spinelloid is a high-entropy phase.

The volume of the spinel solid solution, MgGa204-MgzGeO4, shows a positive deviation from Vegard's Law. Modeling of the cation distribution in the solid solution indicates that this A V is due to a change in the spinel type from inverse towards normal as the Mg2GeO4 content increases.