Entropic Precursor for the B1–B2 Phase Transition of Crystalline Magnesium Oxide at 300 K

Abstract

Calculations for MgO on a 300 K isotherm (as in the works of other authors) show that when compressed by 2–2.5 times, its absolute entropy falls sharply and tends to zero. A synergistic effect is then revealed: low values of entropy on the isotherm for MgO are a precursor of a phase transition that causes the entropy of the crystal to grow abruptly, eliminating the problem of zero entropy. A large group of diatomic solids of the NaCl type is identified that undergo similar phase transitions under compression.