NDLI: Polymorphism and crystal chemistry of Li2.5Ga0.5GeO4, an Li3PO4 analogue

Content Provider	Royal Society of Chemistry (RSC)
Author	Robertson, Alastair D. West, Anthony R.
Copyright Year	1994
Abstract	The structures of γ- and β-Li2.5Ga0.5GeO4, have been determined using Rietveld refinement of X-ray powder diffraction data. They are stoichiometric derivatives of γ- and β-Li3PO4. The arrangements of GeO4/PO4 tetrahedra are the same in each case, but the Li sites, especially Li(2), contain a disordered mixture of Li and Ga in γ- and β-Li2.5Ga0.5GeO4. Such cation disorder is unusual in a stoichiometric phase. The γ phase may be regarded as entropy-stabilised since it exists under equilibrium conditions only at high temperatures, ca. 1200 °C, just below melting: the size mismatch between Li+ and Ga3+ ions and the likely unfavourable enthalpy of mixing associated with Li/Ga disorder is offset by the large entropy contribution to the Gibbs energy at high temperatures. A discussion of possible mechanisms for the β⇌γ transition is given.
Starting Page	457
Ending Page	462
Page Count	6
File Format	PDF
ISSN	09599428
Volume Number	4
Issue Number	3
Journal	Journal of Materials Chemistry
DOI	10.1039/JM9940400457
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	Rietveld Li Gibbs Rietveld refinement Powder diffraction Stoichiometry Tetrahedron Gallium Ion Enthalpy Entropy Gibbs free energy
Content Type	Text
Resource Type	Article
Subject	Chemistry Materials Chemistry

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Polymorphism and crystal chemistry of Li_2.5Ga_0.5GeO₄, an Li₃PO₄ analogue