Anomalous states of the structure of [Rb0.7(NH4)0.3]2SO4 crystals in the temperature range 4.2-300 K

Crystals of [Rb-0.7(NH4)(0.3)](2)SO4 solid solutions are studied using x-ray diffractometry in the temperature range 4.2-300 K. No anomalies are revealed in the temperature dependences of the lattice parameters and the volume of the host unit cell. A series of superstructure reflections observed along the basis axes corresponds to the guest lattice formed in the matrix of the host structure. From analyzing the axial ratio of these structures and their temperature dependences, it is concluded that the structure of the crystal has the form of an incommensurate composite. The guest structure of the composite at room temperature can be considered a set of chains that are not correlated along the b direction. In the plane perpendicular to the chain axes, these chains form a regular framework that is also incommensurate to the host lattice. (C) 2004 MAIK "Nauka / Interperiodica".