Combustion synthesis, structural, magnetic and dielectric properties of Gd3+-doped lead molybdato-tungstates

Gd 3+ -doped lead molybdato-tungstates with the chemical formula of Pb 1−3 x □ x Gd 2 x (MoO 4 ) 1−3 x (WO 4 ) 3 x (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 I 4 1 / 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 (tan δ ≈ 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.