PHASE-TRANSITION SEQUENCE OF LI3THF7 CRYSTALS

Large Li3ThF7 single crystals have been obtained by the Czochralski te chnique. Calorimetric and dielectric investigations over a large tempe rature range (100-800 K) demonstrate the existence of two additional f irst-order phase transitions (at about 281 and 467 K), beside the know n tetragonal-to-orthorhombic one, found at 368 K, 27 K higher than the reported temperature. The knowledge of the structures of these additi onal phases, besides the phase transition mechanisms, can help to prev ent the multiple microcracks which develop in the sample after crystal growth and limit its technological applications. Conductivity measure ments show also the high anisotropic character of the Li+ ion's mobili ty.