Дипольное упорядочение и ионная проводимость в NASICON-подобных структурах типа Na-=SUB=-3-=/SUB=-Fe-=SUB=-2-=/SUB=-(PO-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-

The problems of the structural features, the dielectric and conducting properties of Na_3Fe_2(PO_4)_3 polycrystals prepared by hot pressing have been studied. The Na_3Fe_2(PO_4)_3 polycrystals in the α and β phases are shown to have higher conducting properties than the α and β phases of the single crystals grown by the solution–melt method. The regularities of the appearance of the dipole ordering, the ionic and superionic conductivities related to phase transitions and structural changes in the {[Fe_2(PO_4)_3]^3–}_3∞ rhombohedral crystalline frame during polymorphic transformations are refined. The problems of the relaxation polarization in the α and β phases of Na_3Fe_2(PO_4)_3 are discussed. A model for explaining the dipole ordering and the ionic conductivity in Na_3Fe_2(PO_4)_3 is proposed.

Shear Viscosity of Aqueous Electrolyte Solutions

The kinematic shear viscosity of aqueous electrolyte solutions has been studied. The temperature dependence of this parameter is shown to be described by an exponential formula at T < Td and a formula of the argon-like type at T > Td, where Td is the temperature of the dipole ordering, in the whole considered concentration interval. Main attention is focused on the peculiarities in the temperature and concentration dependences of the shear viscosity in the argon-like interval. It is shown that the root-like concentration dependence can appear, only if the Debye theory of dilute electrolyte solutions is applicable. Beyond its validity domain, the series expansion of the kinematic shear viscosity in the concentration parameter should have an analytical character. The latter behavior is inherent in the concentration dependence of the shear viscosity in the majority of experiments. The error of reproducing the experimental data did not exceed the experimental one, i.e. it was smaller than 4–5%.

Дипольное упорядочение и ионная проводимость в NASICON-подобных структурах типа Na-=SUB=-3-=/SUB=-Sc-=SUB=-2-=/SUB=-(PO_4)-=SUB=-3-=/SUB=-

Problems of the dipole ordering and ionic conductivity of Na_3Sc_2(PO_4)_3 polycrystal that has three polymorphic phases—α, β, and γ—are studied. The features of the α-Na_3Sc_2(PO_4)_3 crystal structure and the dipole ordering and relaxation polarization in the α and β phases are specified. The origin of the dipole ordering in the α phase and the partial dipole disordering in the β-Na_3Sc_2(PO_4)_3, as well as the high ionic conductivity in the β and γ phases of the Na_3Sc_2(PO_4)_3 polycrystal are associated with phase transformations α → β, β → γ that result in structural changes of the rhombohedral {[Sc_2(PO_4)_3]^3–}_3∞ crystalline framework. A model explaining the emergence of the dipole ordering and the ionic conductivity phenomena in Na_3Sc_2(PO_4) is proposed.