Low-Temperature Grüneisen Parameters for Silicon and Aluminum

From measurements of the inertial thermoelastic stress produced by pulse heating a portion of a sample, the Gr\"uneisen parameters of silicon and aluminum as a function of temperature were obtained directly between 5 and 290 ^∘{}K. Pulses of 1.5-MeV average-energy electrons, lasting approximately 40 nsec, were used as the heating agent, and the stresses were recorded with a quartz gauge bonded to the back face of the sample. For silicon, the low-temperature stress measurements indicated a limit of the Gr\"uneisen parameter of about 0.2, which is lower than the value calculated from thermal-expansion data but in agreement with that calculated from pressure derivatives of elastic constants. For aluminum (6061 alloy-97% Al), the low-temperature limit of the lattice Gr\"uneisen parameter was found to be 1.7 and the electronic contribution was estimated to be 1.7 as well, agreeing within experimental uncertainty (approximately 25%) with published values based on thermal-expansion measurements on pure aluminum.