A GRUNEISEN RELATION ON CONSTANT-PRESSURE LINES

Gruneisen's constant, gamma, is ideally temperature-independent on constant-volume lines; a similar constant, lambda, which is ideally temperature-independent on isobaric lines, has been found. The comparison between gamma and lambda shows that both expressions contain the ratio of the volumetric thermal expansion coefficient to the specific heat capacity; gamma has an additional temperature dependence due to the thermal part of the compressibility, whereas lambda has only a slight thermal component due to the volume per unit mass. Lambda has been chosen so that lambda = gamma at the point where the temperature and pressure are both zero. For most materials it is expected that lambda greater-than-or-equal-to gamma with a different temperature dependence. It is shown empirically for a selection of ceramics that lambda is nearly temperature-independent and has a value between 0.7 and 1.4.