THERMAL EXPANSIONS OF FERROELECTRIC LI2GE7O15 AND LINAGE4O9

Thermal expansions x(i) (i = 1, 2, 3) of the crystals of Li2Ge7O15 (LG O) and LiNaGe4O9 (LNG) were measured by means of a strain gauge method down to the liquid helium temperature. They showed anomalies at the C urie temperature T-C. Anomalous parts of the strains below T-C (i.e. s pontaneous strains) of LGO along the b- and c-direction are larger tha n one along the pseudohexagonal a-direction. On the other hand, the th ermal expansion coefficient alpha(2) along the pseudohexagonal b-direc tion of LNG is larger than the others in the paraelectric phase and th e spontaneous strain along the c-direction is only positive. The tempe rature dependence of their spontaneous polarizations measured by a pyr oelectric charge method above the liquid helium temperature was also r eported with the dielectric constants.