No abstract

Gd 3+-doped lead molybdato-tungstates with the chemical formula of Pb 1-3x x Gd 2x (MoO 4) 1-3x (WO 4) 3x (where x = 0.0455, 0.0839, 0.1430, corresponding to 9.53, 18.32, 33.37 mol% of Gd 3+ , 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 I4 1 /a) with the uniform, spherical and oval grains ranging from 5 to 20 m. Individual grains are strongly agglomerated into big clusters with the size even above 50 m. 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 (tan  0.01) below 300 K. Dielectric analysis showed that no dipole relaxation processes in the Gd 3+-doped materials were observed. A fit of dielectric loss spectra of Gd 3+-doped samples by sum of the conductivity and the Havriliak-Negami, Cole-Cole, and Cole-Davidson functions confirmed this effect.