Phase transition in mayenite Ca12Al14O33

A phase transition in Ca12Al14O33 has been discovered and investigated by thermogravimetric analysis, differential scanning calorimetry, dilatometry, and high-temperature X-ray diffraction. The phase transition occurs at 922 ± 45 K (ΔH = −406 ± 13 kJ/mol, ΔS = −440 ± 14 J/(mol K)) and is presumably a first-order one. It does not change the symmetry of the cationic subsystem. The phase transition is difficult to reveal because the material changes its mass, probably by releasing water bound in several different ways.