Thermo-elastic behavior and P/T phase stability of TlAlSiO4 (ABW)

The PIT phase stability and the thermo-elastic behavior of synthetic TlAlSiO4 [ABW framework type, space group Pna2(1), a = 8.2719(2), b = 9.4373(2), c = 5.4180(1) angstrom] have been investigated up to 950 degrees C (at room-P) and up to 8 GPa (at room-T) by means of in situ synchrotron powder diffraction with a diamond anvil cell and with a high-temperature furnace. The Rietveld structure refinement of TlAlSiO4 at room P/T confirms the general structure model previously reported. Only one independent Tl site, with full site occupancy and close to channel wall, represents the extra-framework population. No phase transition has been observed within the temperature- and pressure-range investigated. P-V data were fitted to a second-order Birch-Murnaghan Equation of State (BM-EoS), giving: V-0 = 420.76(5) angstrom(3), K-T0 = 48.8(2) GPa. The evolution of the lattice parameters with pressure shows a significantly anisotropic compressional pattern. The elastic parameters calculated with a "linearized" second-order BM-EoS are: K-T0(a) = 21.96(7) GPa for the a-axis; K-T0(b) = 68(1) GPa for the b-axis, and K-T0(c) = 112(2) GPa for the c-axis. The volume thermal expansion with T was modeled by the polynomial function: V(T)/V-0 = 1 + alpha(0)center dot Delta T + alpha(1)center dot Delta T-2 = 1 + 4.44(3)center dot 10(-5)center dot Delta T - 2.3(3)center dot 10(-9)center dot Delta T-2. The anisotropic thermal scheme is characterized by a negative thermal expansion along [010] (i.e. alpha(0)(b) = -8.5(1)center dot 10(-6) degrees C-1), almost no expansion along [001] (i.e. alpha(0)(c) = 0.9(1)center dot 10(-6) degrees C-1) and a positive expansion along [100] (i.e. alpha(0)(a) = 52.4(1)center dot 10(-6) degrees C-1). A comparative analysis of the thermo-elastic behavior of the isotypic TlAlSiO4 and CsAlSiO4 is carried out. (C) 2014 Elsevier Inc. All rights reserved.