Role of the elastic constants in negative thermal expansion of axial solids

In cubic solids the elastic properties cannot affect the sign of the thermal expansion, but in axial solids negative thermal expansion can arise not only from anisotropy in the Gruneisen functions, but also from elastic anisotropy. The origin of negative thermal linear expansion is discussed for arsenic, graphite, selenium, tellurium and indium. A negative linear compressibility is neither necessary nor sufficient to ensure negative thermal expansion. The extension of the treatment to solids of lower symmetry is outlined.