Elastic properties of the Kondo compounds CexLa1-xB6 (x=0.75 and 0.70)

We have made thermal expansion measurements to examine the characters of an ordered phase IV in the dense Kondo compounds CexLa1-xB6 (x=0.75, 0.70). For both compounds, expansion along the [0 0 1] direction and shrinkage along [1 1 1] with decreasing temperature have been observed in phase IV. These results indicate the lattice distortion from cubic to trigonal structure. A ferro-quadrupole ordering of Oyz, Ozx, Oxy with Γ5 symmetry is a probable candidate for the order parameter of the phase IV