Study on the Incommensurate Nature of the Intermediate Phase of RbD3(SeO3)2 by Neutron Diffraction

Search for an intermediate phase between the para- and ferro-electric phases of RbD 3 (SeO 3 ) 2 was carried out by neutron diffraction. The superlattice reflection at (2, 0, 0.5) in the ferroelectric phase was found to shift to an incommensurate position, (2, 0, 0.5+δ), above the Curie point though the magnitude of the parameter δ is very small. It increases with increasing temperature and reaches to 0.003 at the paraelectric-to-intermediate transition point which is about 3 K above the Curie point.