Thermal expansivity versus pressure at constant temperature: A re‐examination

Results from recent high pressure experiments have shown δ T in the relationship to be constant over significant compressions, one of the original assumptions required to make this relationship valid. We have re‐examined the original derivation of this equation and present a simpler derivation eliminating the previous assumptions. Furthermore, high pressure experiments find (∂lnα/∂lnρ) T is equal in value to l/αK T (∂K T /∂T) P derived from experiments at ambient pressures. From values of −δ T = l/αK T (∂K T /∂T) P at high temperatures, it is asserted that −(∂lnα/∂lnρ) T must lie between 4 and 6 in the lower mantle, a value significantly higher than previously assumed in earth models.