ELECTRIC AND DIELECTRIC-PROPERTIES OF MONOCLINIC BAR2F8 (R EQUALS RARE-EARTH ELEMENTS) SINGLE-CRYSTALS

The ionic conductivity and permittivity of BaR2F8 (R = rare earth elem ent) single crystals with monoclinic BaTm2F8 structure (space group C2 /m) were measured in the temperature range from 300 to 700 K. A pronou nced anisotropy of ionic conductivity and a slight anisotropy of permi ttivity are found. The fastest ionic transport with the lowest activat ion energy (similar to 0.56 eV) and the highest value of the permittiv ity are observed along the a axis. The minimum values of conductivity with the activation energy of 0.75-0.8 eV are observed along the c axi s (e.g. the axis normal to the cleavage plane). The mechanism of the i onic transport in BaTm2F8 structure is discussed.