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Figure 22
Virtual melting point Tm,A of phase A: the Gibbs free energies of phase A, phase B and the liquid as a function of temperature are shown. Phase A is the most stable phase at low temperature, and when the temperature increases phase A converts to phase B before melting. Tm,A and Hm,A cannot be measured directly (at ambient pressure), but Tm,A must lie between TA→B and Tm,B. The temperature dependence of the Gibbs free energies is represented as straight lines for clarity, in reality these lines are curved. A similar situation occurs when a phase decomposes before melting. The most stable phase at each temperature is shown in bold.

IUCrJ
Volume 1| Part 1| January 2014| Pages 61-73
ISSN: 2052-2525
https://doi.org/10.1107/S2052252513026511