Phase transitions in leucite, KAISi2O6

✍ Scribed by Dorian M. Hatch; Subrata Ghose; Harold T. Stokes

• Publisher: Springer-Verlag
• Year: 1990
• Tongue: English
• Weight: 885 KB
• Volume: 17
• Category: Article
• ISSN: 0342-1791
• DOI: 10.1007/bf00201453

✦ Synopsis

An order parameter treatment of the phase transitions in leucite, KA1Si206, at approximately 950 and 920 K: Ia3d(cubic)--* I41/acd(tetragonal) --,I41/a(tetragonal) is presented in terms of Landau theory and induced representation theory. The AI-Si order with decreasing temperature is taken as the primary order parameter to which other distortions (K § ion displacements, strain components, etc.) couple linearly. The expected A1-Si ordering behavior and the associated K § ion displacements for both transitions are derived and the resulting twin domain orientations are listed. The sequence of phase transitions results from a coupling of F3 § and F4 + representations. The Landau free energy for the five-dimensional reducible representation has been simplified to two components resulting in a linearquadratic coupling of the components. Possible phase diagrams are derived by free energy minimization. The cubic-~ tetragonal transition is first-order, whereas the tetragonal-tetragonal transition may be second order. A tricritical point exists at which the first-order transition changes to second-order.