N. I. Sorokin

Frequency response of the low-temperature ionic conductivity of single crystals R1 − yMyF3 − y (R = La-Er; M = Ca, Sr, Ba, Cd)

The frequency response (10−1–10−7 Hz) of the ionic conductivity σ of R1 − yMyF3 − y single crystals (R is a rare-earth element, and M stands for an alkaline-earth element and Cd) with a tysonite structure is studied over a wide temperature range (114–410 K), which includes (for the first time for these phases) the interval below room temperature. The dependences σ(ν) obtained are discussed within the hopping relaxation model. The characteristics of the relaxation and migration processes and the carrier concentration and mobility are determined.

Superionic conductivity of the heterovalent solid solutions R1−xMxF3−x (R=REE, M=Ca, Ba) with tysonite-type structure

The fluorine-ion conductivity of anion-deficient solid solutions R1−xCaxF3−x and R1−xBaxF3−x having the tysonite (LaF3) structure was investigated by the impedance spectroscopy method. R1−xCaxF3−x (R=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho) and R1−xBaxF3−x (R=La, Pr, Nd) single crystals were grown from the melt by the Bridgman-Stockbarger method. The electrophysical measurements were performed in the frequency range 5−5×105 and temperature range 300–700 K. The temperature dependences of the electrical conductivity for the crystals studied is determined by the migration of fluorine anions along various structural positions. It is shown that, from the standpoint of increasing the conductivity of tysonite matrices RF3 (R=La, Pr, Nd), doping by CaF2 and BaF2 is less promising than SrF2.

Specific features of anion transfer in superionic conductors based on MF2 (M=Pb and Cd)

Fluoride-conducting superionic conductors in the PbF2-CdF2, PbF2-SnF2, PbF2-ScF3, CdF2-HoF3, and CdF2-ErF3 systems are studied over a wide range of temperatures (130–1073 K). The thermal stability of the electrical conduction characteristics and the smeared transition to the superionic state (10−1-1 S/cm) are investigated in PbF2, Pb0.67Cd0.33F2, and Pb1−xScxF2+x (x=0.01 and 0.1) single crystals and a PbSnF4 polycrystalline sample. In the Cd1−xRxF2+x solid solutions (R=Ho and Er, 0.02≤x≤0.20), the crossover from one mechanism of ion transfer to the other mechanism is revealed in the temperature range 600–800 K. The correlation between the anion transfer and specific features in the defect structure of crystals is discussed.

Ionic conductivity of double sodium-scandium and cesium-zirconium molybdates

The electrical properties of the Na3Sc(MoO4)3 and Cs2Zr(MoO4)3 compounds are investigated using impedance spectroscopy (1–106 Hz) in the temperature range 100–650°C. Double molybdates in the form of a fine-crystalline powder are obtained by solid-phase synthesis in air at 450–600°C for 20–50 h. It is found that the temperature dependence of the ionic conductivity of ceramic samples exhibits anomalies at temperatures of 605 ± 5°C for Na3Sc(MoO4)3 and 425 ± 15°C for Cs2Zr(MoO4)3 due to the phase transitions, which are confirmed by the data of thermal analysis. Above the superionic transitions, the ionic conductivity reaches 0.084 S/cm (650°C) for Na3Sc(MoO4)3 and 0.002 S/cm (462°C) for Cs2Zr(MoO4)3.

Specific features of anion transfer in HoF3 crystals at high temperatures

The anionic conductivity of HoF3 single crystals with a β-YF3 structure (orthorhombic crystal system, space group Pnma) is investigated over a wide range of temperatures (323–1073 K). The unit cell parameters of HoF3 crystals are as follows: a=0.6384±0.0009 nm, b=0.6844±0.0009 nm, and c=0.4356±0.0005 nm. It is revealed that the conductivity anisotropy of the HoF3 crystals is insignificant over the entire temperature range covered. The crossover from one mechanism of ion transfer to another mechanism is observed near the critical temperature Tc≈620 K. The activation enthalpy of electrical conduction is found to be ΔH1=0.744 eV at TTc. The fluorine vacancies are the most probable charge carriers in HoF3 crystals. The fluorine ionic conductivities at temperatures of 323, 500, and 1073 K are equal to 5×10−10, 5×10−6, and 2×10−3 S cm−1, respectively.

Ion transport in the anion-deficient nonstoichiometric phases La0.95(Ba1−xSrx)0.05F2.95 (0⩽x⩽1)

The fluoride-ion conductivity of the nonstoichiometric tysonite phases La0.95(Ba1−xSrx)0.05Fe2.95 (0⩽x⩽1) is investigated by impedance spectroscopy. Electrophysical measurements are performed in the frequency range 5–5×105 Hz and temperature range 300–700 K. A discontinuity is observed in the temperature dependence of the conductivity at Tc=410–430 K. The behavior of the temperature dependence of the electrical conductivity is explained within a transport model taking into account the migration of fluoride ions between different inequivalent structural sites. The maximum value of the conductivity at room temperature (293 K) is 2×10−4 Ω−1 cm−1 for the solid solution La0.95Sr0.05F2.95. The fluorine-ion conductivity in La0.95(Ba1−xSrx)0.05F2.95 single crystals is almost an order of magnitude larger than the value for the commercial solid electrolyte La0.992Eu0.008F2.992 (a fluorine-selective membrane) having a tysonite structure.

Na + -ion conductivity of double phosphate Na 3 Sc 2 (PO 4 ) 3 in the region of the β-γ transition

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.

Electrical conductivity of superionic conductor single crystals Li4B7O12Cl1 − xBrx (x ∼ 0.3)

The temperature dependence of the ionic conductivity of boracite single crystals Li4B7O12Cl1 − xBrx (x ∼ 0.3, cubic system, space group

Superionic transitions and conductivity anisotropy in Na4.6FeP2O8.6F0.4 single crystals

Foverline {43} c