A singular thermodynamically consistent temperature at the origin of the anomalous behavior of liquid water
The density maximum of water dominates the thermodynamics of the system under ambient conditions, is strongly P-dependent, and disappears at a crossover pressure Pcross ~ 1.8 kbar. We study this variable across a wide area of the T-P phase diagram. We consider old and new data of both the isothermal compressibility KT(T, P) and the coefficient of thermal expansion αP(T, P). We observe that KT(T) shows a minimum at T* ~ 315+/-5 K for all the studied pressures. We find the behavior of αP to also be surprising: all the αP(T) curves measured at different P cross at T*. The experimental data show a ``singular and universal expansivity point'' at T* ~ 315 K and αP(T*) ~= 0.44 10-3 K-1. Unlike other water singularities, we find this temperature to be thermodynamically consistent in the relationship connecting the two response functions.