THERMAL-EXPANSION ASSOCIATED WITH THE CHARGE-DENSITY WAVE IN K0.3MOO3

Thermal expansion was measured in two crystals of blue bronze (K0.3MoO3). At the Peierls temperature, the expansion coefficients exhibited a small steplike decrease along the chain direction, a nearly negligible change perpendicular to the cleavage planes, and a large steplike increase in the third, mutually orthogonal direction. Substantial departures from mean-field behavior were attributed to fluctuations, the width of the critical region was 8 K, and the temperature dependence was consistent with the three-dimensional XY model. The anisotropy of the steps was interpreted in terms of a transverse-optical periodic lattice distortion in an anharmonic lattice. Specimen length did not vary with electrical bias.