Kinetics of the incommensurate to commensurate transition in the solid solution (NH4)2(BeF4)0.92(SO4)0.08

The time evolution of the incommensurate to commensurate transition is presented for the solid solution (NH4)2(BeF4)0.92(SO4)0.08. After annealing of the sample in the paraelectric phase, the temperature is rapidly decreased and then stabilized in the incommensurate phase. From this time the diffraction profile of the satellite is repeatedly measured for more than 2200 min. The incommensurate phase progressively disappears in favour of the commensurate low-temperature phase and of a new intermediate state. This new state seems to play the leading role in the transition process. An interpretation based on nucleation of antistripples or deperiodization lines is suggested.