Cubic KR₃F₁₀ (R = Y, Tb) single crystals have been successfully grown using the Bridgman technique. Growth of crystals of this type is complicated due to the hygroscopicity of potassium fluoride and melt overheating. The solution to the problem of oxygen-incorporated impurities has been demonstrated through the utilization of potassium hydrofluoride as a precursor. In this study, the crystal quality, structure features, and optical, thermal and electrophysical properties of KR₃F₁₀ were examined. Data on the temperature dependences of conductivity properties of KTb₃F₁₀ crystals were obtained for the first time. These crystals indicated thermal conductivity equal to 1.54 ± 0.05 Wm⁻¹K⁻¹ at room temperature caused by strong phonon scattering in the Tb-based crystal lattice. Ionic conductivities of KY₃F₁₀ and KTb₃F₁₀ single crystals were 4.9 × 10⁻⁸ and 1.2 × 10⁻¹⁰ S/cm at 500 K, respectively, and the observed difference was determined by the activation enthalpy of F⁻ ion migration. Comparison of the physical properties of the grown KR₃F₁₀ crystals with the closest crystalline analog from the family of Na_0.5−xR_0.5+xF_2+2x (R = Tb, Y) cubic solid solutions is reported.

ScF₃ optical quality bulk crystals of the ReO₃ structure type (space group $Pm\overline{3}m$ , a = 4.01401(3) Å) have been grown from the melt by Bridgman technique, in fluorinating atmosphere for the first time. Aiming to substantially reduce vaporization losses during the growth process graphite crucibles were designed. The crystal quality, optical, mechanical, thermal and electrophysical properties were studied. Novel ScF₃ crystals refer to the low-refractive-index (n_D = 1.400(1)) optical materials with high transparency in the visible and IR spectral region up to 8.7 µm. The Vickers hardness of ScF₃ (H_V ~ 2.6 GPa) is substantially higher than that of CaF₂ and LaF₃ crystals. ScF₃ crystals possess unique high thermal conductivity (k = 9.6 Wm⁻¹К⁻¹ at 300 K) and low ionic conductivity (σ = 4 × 10⁻⁸ Scm⁻¹ at 673 К) cause to the structural defects in the fluorine sublattice.

A series of nonstoichiometric La_1–yBa_yF_3–y (0 ≤ y ≤ 0.12) single crystals with a tysonite-type structure (sp. gr. P-3c1) was grown from the melt by the directional crystallization method in a fluorinating atmosphere, and some physical properties were characterized. The concentration dependence of electrical conductivity σ_dc(y) La_1–yBa_yF_3–y crystals was studied. The composition of the ionic conductivity maximum for this solid electrolyte was refined. It was confirmed that the maximum conductivity σ_max = 8.5 × 10^–5 S/cm (295 K) was observed at the composition y_max = 0.05 ± 0.01. Analysis of the electrophysical data for the group of tysonite-type solid electrolytes R_1–yM_yF_3–y (M = Ca, Sr, Ba, Eu²⁺ and R = La, Ce, Pr, Nd) showed that the compositions of the maxima of their conductivity were close and amount to y = 0.03−0.05. This fact indicates a weak influence of the size effect (ionic radii R³⁺ and M²⁺) on the value of y_max for R_1–yM_yF_3–y solid electrolytes.

The Na⁺-ion conductivity σ of double phosphate Na₃Sc₂(PO₄)₃ in the region of the β-γ transition has been studied using impedance spectroscopy (1–10⁶ Hz). The polycrystalline sample of Na₃Sc₂(PO₄)₃ has been prepared by solid-phase synthesis and ceramic technology. It has been found that, upon the β-γ transition, the conductivity σ of Na₃Sc₂(PO₄)₃ suffers a ∼1.5-fold jump at 470 ± 2 K upon heating and a ∼2.5-fold jump at 430 ± 4 K upon cooling (the temperature hysteresis of the jump in σ is 40 K). For double sodium-scandium phosphate γ-Na₃Sc₂(PO₄)₃ in the superionic state, σ attains 0.07 S/cm at 700 K and the ion transport activation enthalpy is 0.42 ± 0.02 eV.

The ionic conductivity σ of KMgCr(MoO₄)₃ crystal has been investigated in a temperature range of 575–932 K by impedance spectroscopy in the frequency range of (5–5) × 10⁵ Hz. Ternary molybdate was obtained from the initial MgMoO₄ and KCr(MoO₄)₂ reagents by solid-phase technique in air at 923–973 K for 200 h. The temperature dependence σ(T) of a ceramic sample exhibits a jump of σ by a factor of about 4 at 833 ± 5 K, which is caused by the first-order phase transition. The σ value above the phase-transition temperature reaches 6 × 10^–4 S/cm (932 K) at an ion-transport activation enthalpy of 0.84 ± 0.05 eV. The most likely carriers in KMgCr(MoO₄)₃ are K⁺ cations.

The frequency (ν = 10⁻¹–10⁷ Hz) dependences σ(ν) of the conductivity of single crystals of the Pb_0.67Cd_0.33F₂ superionic conductor with the fluorite-type structure (CaF₂) in the temperature range of 132–395 K have been studied. The dependences σ(ν) have been discussed in the framework of the hopping relaxation of ionic carriers, which are mobile anions F⁻. From experimental curves σ(ν), the direct-current (dc) conductivity σ_dc and the average charge carrier hopping frequency ν_h have been determined. This has made it possible to calculate the charge carrier mobility μ_mob and charge carrier concentration n _mob in these crystals. At room temperature (293 K), the electrical parameters are σ_dc = 1.6 × 10⁻⁴ S/cm, ν_h = 2.7 × 10⁷ Hz, μ_mob = 2.0 × 10⁻⁷ cm²/(s V), and n _mob = 5.1 × 10²¹ cm⁻³.