Monophasic polycrystalline samples of Pb_1−3x□_xPr_2x(MoO₄)_1−3x(WO₄)_3x solid solution with limited homogeneity (0 < x ≤ 0.2222) and cationic vacancies (□) have been prepared by high-temperature annealing of PbMoO₄/Pr₂(WO₄)₃ mixtures composed of 40.00 mol% and less of praseodymium tungstate. Initial reactants and obtained ceramic materials were characterized by XRD, simultaneous DTA–TG, IR and UV–Vis–NIR techniques. The X-ray diffraction analysis showed that the monophasic samples crystallize in a tetragonal symmetry, with space group I4 ₁ /a (a scheelite-type structure), and PbMoO₄ is a matrix of Pb_1−3x□_xPr_2x(MoO₄)_1−3x(WO₄)_3x solid solution. Thermal stability of samples under study strongly depends on concentration of Pr³⁺ ions. The Pb_0.9286□_0.0238Pr_0.0476(MoO₄)_0.9286(WO₄)_0.0714 solid solution (x = 0.0238) shows the highest melting point (1055 °C), and this value is slightly higher than the melting point of PbMoO₄ (1040 °C). Lead molybdate and samples of Pb_1−3x□_xPr_2x(MoO₄)_1−3x(WO₄)_3x solid solution are insulators having indirect band gap E _g > 3 eV. The observed band gap of monophasic samples shows a nonlinear variation with a change of Pr³⁺ ions concentration in the scheelite framework.

A series of Mn²⁺-doped and Eu³⁺-co-doped calcium molybdato-tungstates, i.e., Ca_1−3x−yMn_y⌷_xEu_2x(MoO₄)_1−3x(WO₄)_3x (0 < x ≤ 0.2222 when y = 0.0200 and 0 < y ≤ 0.0667 when x = 0.1667, ⌷ represents vacancy) materials were successfully synthesized via high-temperature annealing. XRD results confirmed the formation of single, tetragonal scheelite-type phases (space group I4₁/a). A change in both lattice constants (a and c), lattice parameter ratio c/a and progressive deformation of MoO₄/WO₄ tetrahedra with increasing Eu³⁺ as well as Mn²⁺ contents were observed. The melting point of doped materials is lower than the melting point of pure matrix, i.e., CaMoO₄. New materials exhibit strong absorption in the UV range. They are insulators with the optical direct band gap (E_g) higher than 3.50 eV. The E_g values nonlinearly change with increasing dopants concentrations. EPR measurements allowed to establish the nature of magnetic interactions among Mn²⁺ ions. Additionally, EPR spectra were sensitive on both parameters: Mn²⁺ and Eu³⁺ concentration.

Gd³⁺-doped lead molybdato-tungstates with the chemical formula of Pb_1−3x□_xGd_2x(MoO₄)_1−3x(WO₄)_3x (where x = 0.0455, 0.0839, 0.1430, corresponding to 9.53, 18.32, 33.37 mol% of Gd³⁺, respectively, as well as □ denotes cationic vacancies) were successfully synthesized via combustion route. The XRD and SEM results confirmed the formation of single-phase, tetragonal scheelite-type materials (space group I4₁/a) with the uniform, spherical and oval grains ranging from 5 to 20 µm. Individual grains are strongly agglomerated into big clusters with the size even above 50 µm. The magnetic measurements as well as the Brillouin fitting procedure showed paramagnetic state with characteristic superparamagnetic-like behaviour and the short-range ferromagnetic interactions. The electrical and broadband dielectric spectroscopy studies revealed insulating properties with the residual electrical n-type conduction of 2×10⁻⁹ S/m and low energy loss (tanδ ≈ 0.01) below 300 K. Dielectric analysis showed that no dipole relaxation processes in the Gd³⁺-doped materials were observed. A fit of dielectric loss spectra of Gd³⁺-doped samples by sum of the conductivity and the Havriliak-Negami, Cole-Cole, and Cole-Davidson functions confirmed this effect.