Location of the tricritical point for the melting of commensurate solid krypton onZYXgraphite

Detailed vapor-pressure isotherms of krypton on Union Carbide's ZYX exfoliated graphite are used to determine the distribution of adsorption potentials and to locate the tricritical point where the melting of the commensurate krypton solid becomes continuous. We find from isotherms in the fluid-solid coexistence region an asymmetric, 1.5-K full width at half maximum distribution, comparable to other exfoliated graphites. A least-squares-fitting procedure indicates a tricritical point at 117±{}2 K in agreement with previous thermodynamic experiments but in sharp contrast to recent x-ray scattering experiments on the same type of substrate.