Conductivity and thermodynamic properties of solid solutions (1 x)RbNO3-xRbNO(2) were investigated over entire concentration range of 0 III and III <-> II, so that highly conducting phase III becomes stable at low temperatures. The introduction of smaller NO2- anions results in the increase in the conductivity of the RbNO3-III phase, the activation energy and a pre-exponential factor of conductivity decrease with the doping and III-IV transition becomes diffusive. A possible reason of these effects is a strong influence of nitrite ions to the orientational disorder of the anionic sublattice of RbNO3. (C) 2010 Elsevier B.V. All rights reserved.