Effect of Ca2+ site substitution on structural, optical, electrical and magnetic properties in Nd3+ and Mn2+-co-doped calcium molybdato-tungstates

Ca1- 3x-yMny[]xNd2x(MoO4) (1-3x)(WO4) (3x) molybdato-tungstates ([]denotes vacant sites) were successfully synthesized by high-temperature solid-state reaction. New materials crystallize in scheelite-type structure within whole homogeneity range of solid solution (x < 0.2000 and y = 0.0200). Morphological features and particle size distribution were investigated by SEM and laser diffraction methods, respectively. Spectroscopic measurements in the UV-vis range was carried out to determine optical direct band gap (E-g), Urbach energy (E-U) and confirmation of structural disorder. Refractive index (n) was calculated using four different models. Magnetic studies revealed paramagnetic behavior with long-range ferrimagnetic and short-range antiferromagnetic interactions. New materials showed weak n-type electrical conductivity and thermoelectric power factor (S-2 sigma) that strongly depends on Nd3+ ions content. Dielectric parameters, i.e. relative permittivity (epsilon(r)) and energy loss (tand) are insignificantly dependent on Nd3+ ions concentration. These effects were considered in terms of structural defects, thermal activation of charge carriers, and the Maxwell-Wagner polarization.