Li1.5Rb0.5MoO4: Ferroelectric properties and characterization of phase transitions by Raman spectroscopy

The new Li1.5Rb0.5MoO4 compound has been synthesized by solid state reaction route, which crystallized at room temperature in the monoclinic system (space group P21) with the lattice parameters are a = 15.3157 Å, b = 14.3226 Å, c = 9.0217 Å, β = 97.741°, and V = 1960.97 Å3. Differential scanning calorimetric (DSC) disclosed two endothermic peaks at T1 = 393 K and T2 = 410 K. The temperature dependence of the dielectric constant at different frequency proved that this compound is ferroelectric below approximately 412 K. Temperature dependent variation of the dielectric constant showed a diffused phase transition which can be well described by fitting the modified Curie-Weiss relation, 1ε′−1ε′r,max=(T−Tmax)γC. Raman scattering studies (200-1100 cm−1) were performed in the temperature range 353-503 K. The analysis of the wavenumber, intensity and the half-width based on the order-disorder model allowed to obtain information relative to the thermal coefficient and the activation energy near the transitions phase.