Microstructure and physical properties of superionic eutectic composites of the LiF-RF3 (R = rare earth element) system

For the eutectic composites of the LIF-RF3 (R = rare earth element, Y) syst em, which were prepared from the melt, the relations between (1) the electr ical properties (fast fluoride ion conduction and dielectric response) of t he composites and those of both corresponding single phases, (2) the compos ition, the preparation technique, the microstructure and the electrical pro perties of the composites, are examined. In the composites containing a tys onite-structured phase, the conductivity is significantly lower than that o f the corresponding RF3 single crystal. A pronounced conductivity enhanceme nt occurs in the LiF-LiGdF4 composite only. In the LiF-SmF3 composite, the significant upward jump of the conductivity is incidental to the orthorhomb ic --> tysonite phase transition at 496+/-5 degrees C. Simulation of the re sidual stress field in the fibrous LiF-TbF3 composite is performed. The inf luence of this field on the crack deflection is discussed. (C) 1999 Elsevie r Science B.V. All rights reserved.