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The thermal conductivity of LiKSO 4 ferroelastic crystals was measured alon$ the three principal crystallographic axes in the vicinity of its high temperature phase transition at 750 K. The data showed an anomalous behaviour in the temperature dependence of the thermal conductivity in the transition region of width of about 25 degrees. The anomaly in the phonon contribution to the conductivity was referred to the freezing-in of either optic-and/or acousticmodes of lattice vibrations in the near vicinity of the phase transition. The results aredi~ussed in terms of scattering mechanisms of energy carders.Lithium potassium sulphate, LiKSO4, crystal is pyroelectric [1] with a hexagonal symmetry at room temperature. The system corresponds to the space group P6 a and there are two molecules in the hexagonal unit cell. Extensive studies on the physical properties of LiKSO 4 in different temperature ranges have been reported [2][3][4][5].These studies have shown that the crystal undergoes several phase transitions. In the high temperature region, the crystal exhibits a structural phase transition from hexagonal to orthorhombic system [7] at about 705 K. The next and the last high temperature phase transition, probably back to hexagonal system, was observed near 940 K [2]. These high temperature phase transitions were so far the subject of several experlmental]nvestigations [4, 8-

The ferro-paramagnetic phase transition in dilute manganese-nickel base alloys is investigated through a qualitative study of their thermal conductivity as a function of temperature in the phase transition region. A (V-0) relation is applied to measure the ratio between thermal and electrical conductivity of two samples having Mn concentration: 1.17 at. % and 1.82 at. %. The thermal conductivity results were evaluated using the electrical resistivity data obtained for the same samples, but from a separate experiment. The results are compared with previous measurements on pure Ni and Fe, and their alloys. The validity of the Wiedmann-Franz law in the vicinity of the transition is examined.