| Abstrakt: | Electrical resistivity, dielectric constant, thermoelectric power, magnetic susceptibility,
magnetization, and electron paramagnetic resonance measurements carried out on MPr2W2Oio
(M = Cd, Co, Mn), CdRE2W20 ,o (RE = Y, Nd, Sm, Gd-Er), RE2W20 9 (RE = Pr, Nd, Sm-Gd),
CuEu2W2Oio and Cu3Eu2W4 0 i8 compounds revealed an insulating State and both a weak hole
and electron conduction as well as a paramagnetic state above 4.2 K for all compounds under
study. Only for MnPr2W2Oio a ferrimagnetic order below the Curie temperature Tc = 45 K.
was observed. The tungstates containing Y, Sm and Eu elements showed a weak response to
the magnetic field characteristic for the multiplet widths comparable to the thermal energy.
The broadband dielectric spectroscopy measurements revealed anomaly large value of
the relative permittivity (er=884) for MnPr2W2Oio, the smaller one (er=l 56) for CoPr2W2Oio
and the smallest one (er=22) for CdPr2W2Oio at Iow frequency (v=0.1 Hz) and above room
temperature in the insulating and paramagnetic State. Below 273 K the relative permittivity
(sr~24) does not depend significantly on frequency. For all CdRE2W2Oio tungstates (RE = Y,
Nd, Sm, Gd-Er) a relatively Iow dielectric permittivity (er ~ 15) was also found. In case o f
CuEu2W2Oio £r ~ 29 and for Cu3Eu2W4 0 is £r ~ 217 were measured. The main conclusion is
that only these ions which have the unscreened electrons on the unfilled shells are responsible
for the colossal dielectric effect.
All the tungstates under study show the values o f the magnetic permittivity ^ir < 1.023,
characteristic for the paramagnets. Some o f them like as Gd2W2C>9, CdNd2W2Oio and
CdGd2W2Oio showed the superparamagnetic-like behaviour connected with the weak spinorbit
coupling. |