Specific features of anion transfer in HoF3 crystals at high temperatures

Abstract

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 T Tc. 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.