Heat capacity and dielectric studies of ferroelectric superionic conductor RbNbWO6

Heat capacity and dielectric properties of RbNbWO6 were measured as a function of temperature. The heat capacity measurements revealed the presence of two discontinuous phase transitions at 356.5 and 361.6 K. The former transition was attributed to a transition from the low-temperature tetragonal ferroelectric phase to a phase of unknown symmetry, and the latter to a transition to the cubic phase. The dielectric study revealed the presence of only one and broad anomaly below 310 K. The real and imaginary parts of dielectric permittivity show pronounced shifts of the maxima towards higher temperature with increasing frequency. This behaviour has been attributed to a relaxation process and it seems to be not correlated with the paraelectric–ferroelectric phase transition.