Phase diagrams of the Blume–Emery–Griffiths model with site dilution

Abstract Cluster variational method in pair approximation has been extended for the description of the site-diluted Blume–Emery–Griffths model with spin 1. The phase diagrams for the case of dilution are discussed in the presence of biquadratic interactions and single-ion anisotropy. In particular, the critical concentrations for the ferromagnetic and staggered quadrupolar phases, as well as the shift of tricritical point as a result of dilution have been studied. The numerical calculations are presented for a bilayer system with the coordination number z=5.