Phase coexistence in the deuteron glass Rb-0.9(ND4)(0.1)D2AsO4 proven by neutron diffraction

Neutron diffraction technique has been used to study the transitions from t he paraelectric (PE) phase to the ferroelectric (FE) one in the deuteron gl ass crystal Rb-0.9(ND4)(0.1)D2AsO4 (DRADA-10). The crystal shows PE hk0 dif fraction spots splitting into spot patterns from domains, 4 spots from 4 FE domain types. A more complex phase behavior that the one corresponding to a typical PE-FE phase transition has been found. Coexistence of FE and PE f eatures together with incommensurate correlations in the low temperature ph ase has been discovered. The intensity of the spots associated with the FE domains indicates the fraction of the crystal in the low-temperature phase. For DRADA-10 there is a fairly wide temperature range (7-10 K) over which these spots coexisted with spots remaining from the paraelectric phase.