A new commensurate phase on the theoretical phase diagram of the [N(CH3)4]2CuCl4 crystal

A theoretical phase diagram of the [N(CH 3 ) 4 ] 2 CuCl 4 crystal with a new commensurate phase characterized by a dimensionless wavenumber q = 2/5 is constructed on a plane specified by two coefficients of the thermodynamic potential. This diagram is used as the basis for the construction of a theoretical pressure-temperature ( P-T ) phase diagram. The theoretical P-T phase diagram thus obtained is compared with the experimental P-T phase diagram.