The Thermal Expansion of the Bi Lattice Between 25° and 530° Abs.

The thermal expansion of the lattice of Bi crystals between 25^∘{} and 530^∘{} abs. is measured with a Bragg spectrometer equipped with a movable slit between crystal and ionization chamber. The 2d, 3d and 5th orders of Mo Kα reflections on (111) were used. αII thus obtained varies from 8.3×{}10^-6 to 17.4×{}10^-6 at 25^∘{} abs. and 120^∘{} abs., respectively, beyond the latter temperature it stays unchanged until the melting point. Only the range between -15^∘{}C and +75^∘{}C forms an exception where the expansion coefficient drops to 13.8×{}10^-6. This seems to indicate the existence of a separate "phase," not characterized by a change of the lattice configuration and confirms certain previous findings of discontinuities at +75^∘{}. A definite divergence between the lattice and the integral expansion beginning 30^∘{} before the melting point was found. The Gr\"uneisen rule (αcₚ=const) is found to hold in first approximation for the whole temperature range. The relation of the αII values obtained to those of other authors is discussed.