Lattice Constants and Thermal Expansivities of Silicon and of Calcium Fluoride between 6° and 322°K

Abstract

An x‐ray back‐reflection, rotating‐camera technique has been used to obtain lattice constants and thermal expansivities of single‐crystal silicon and calcium fluoride. Absolute expansivity was obtained over a broad range with an error less than 3 ppm. For silicon, this absolute method discriminates between earlier experiments showing some disagreement, and establishes with improved precision the temperature variation of the Grüneisen parameter γ in the region of particular interest (γ<0). For calcium fluoride the present x‐ray measurements test a prediction of Ganesan and Srinivasan that γ should rise sharply below about 80°K. The prediction is not confirmed.