The standard state of cerium

Based on two studies carried out about 20 years apart, it was found that th e double close-packed hexagonal beta Ce phase slowly transformed to the fac e-centered cubic gamma Ce phase at room temperature and ambient pressure. T his indicates that gamma Ce is the stable modification at standard temperat ure and pressure (i.e., 298 K and 1 atm), The beta Ce <----> gamma Ce equil ibrium temperature at 1 atm, the heat of transformation, the temperature/pr essure phase diagram, and the heat capacities of beta Ce and gamma Ce are p resented.