High-temperature synchrotron powder diffraction investigation of thermal expansion, strain and microstructure for the co-elastic α ↔ β hexacelsian transition

High-temperature investigations of thermal expansion, strain and microstructure of the α ↔ β-hexacelsian reversible phase transition are reported. HexacelsianLTA and hexa-celsianFAU were synthesised from LTA and FAU zeolites, respectively. Only the former show discontinuities near the transition temperature, ∼ 580 K. The discontinuity in the thermal expansion near the transition temperature for the α ↔ β-hexacelsianLTA suggest a co-elastic character for the phase transition. A distortion of the co-ordination polyhedra and ordering of framework cations induce this phase transition. The absence of discontinuities for hexacelsianpFAU suggests non-existence of a phase transition. The similarities in the measured and calculated values for α-hexacelsianLTA and hexacelsianPAU suggest that hexacelsianFAU crystallise exclusively as the β-form.