Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite

Abstract

Yeelimite, Ca 4 [Al 6 O 12 ]SO 4 , is outstanding as an aluminate sodalite, being the framework of these type of materials flexible and dependent on ion sizes and anion ordering/disordering. On the other hand, yeelimite is also important from an applied perspective as it is the most important phase in calcium sulfoaluminate cements. However, its crystal structure is not well studied. Here, we characterize the room temperature crystal structure of stoichiometric yeelimite through joint Rietveld refinement using neutron and X-ray powder diffraction data coupled with chemical soft-constraints. Our structural study shows that yeelimite has a lower symmetry than that of the previously-reported tetragonal system, which we establish to likely be the acentric orthorhombic space group Pcc2, with a √2a×√2a×a superstructure based on the cubic sodalite structure. Final unit cell values were a=13.0356(7) Å, b=13.0350(7) Å, and c=9.1677(2) Å. We determine several structures using density functional theory calculations, with the lowest energy structure being Pcc2 in agreement with our experimental result. Yeelimite undergoes a reversible phase transition to a higher-symmetry phase which has been characterized to occur at 470ºC by thermodiffractometry. The higher-symmetry phase is likely cubic or pseudo-cubic possessing an incommensurate superstructure, as suggested by our theoretical calculations which show a phase transition from an orthorhombic to a tetragonal structure. Our theoretical study also predicts a pressure-induced phase transition to a cubic structure of space group I43m. Finally, we show that our reported crystal structure of yeelimite enables better mineralogical phase analysis of commercial calcium sulfoaluminate cements, as shown by R F values for this phase, 6.9% and 4.8% for the previously published orthorhombic structure and for the one reported in this study, respectively.

Hydration studies of calcium sulfoaluminate cements blended with fly ash

“…The ACn content of this CSA cement,~15 wt.%, is slightly higher than that found for OPC cements,~10 wt.% [41,42], likely due to the lower clinkering temperature leading to smaller particle sizes and microstrains and defects-bearing crystals. The crystal structure descriptions for each phase were those detailed elsewhere [15], except for ye'elimite, where a reviewed orthorhombic C 4 A 3 S has been used [43]. The ACn content in FA is~85 wt.%, where mullite and quartz and some other crystalline minor phases (hematites, magnesium-ferrite, lime and periclase) are also present as crystalline fraction.…”

Pseudocubic Crystal Structure and Phase Transition in Doped Ye’elimite

“…The general formula refers to a structure that is (ideally) a body-centered cubic unit cell with a lattice parameter of 9 Å and where M is a relatively lowcharged caged cation such as Ca, Na or Sr 2 ; T occupies tetrahedral site(s) and is typically Si or Al; and X is the looselybonded caged anion which is either spherical (in the case of Cl) or tetrahedral (in the case of SO 4 , WO 4 , and CrO 4 ). Sodalites are interesting materials for several reasons such as their ferroic phase transition 3 from the high-temperature cubic phase to complex superstructures at lower temperatures.…”

“…Stoichiometric calcium sulfoaluminate or ye'elimite, Ca 4 [Al 6 O 12 ]SO 4 , can be described as a sodalite where M = Ca, T = Al, and X =SO 4 , and crystallizes as a tectoaluminosilicate sodalite structure 4 . This structure was first analyzed by Hanstead and Moore 5 using X-ray powder diffraction, 6 and Saalfeld and Depmeier 7 reported atomic parameters for a cubic crystal structure with space group I ̅ 3m and a=9.195 Å.…”

“…The structure of stoichiometric ye'elimite has been recently established as orthorhombic 4 at room temperature and cubic 9 at high temperatures. The objective of this study is to clarify the crystal structure of doped (disordered) ye'elimite.…”

Study on Sintering System of Calcium Barium Sulphoaluminate by XRD Quantitative Analysis

“…Hargis et al refined the three crystal systems separately by Rietveld refinement and showed that the fitting result of the orthorhombic is the best [11]. Cuesta et al indicated that CSA mineral could be orthorhombic and that orthorhombic crystal sometimes would transform into the cubic at around 470 °C [12,13]. Andac et al also showed that crystal system transition occurred at around 470 °C [14].…”