Thermodynamics of the incommensurate state in Rb_2WO_4: on the Lifshitz point in A`A``BX_4 compounds

I. Luk'yanchuk, A. Jorio, P. Saint-Gregoire

We consider the evolution of the phase transition from the parent hexagonal phase $P{6}_3/mmc$ to the orthorhombic phase $Pmcn$ that occurs in several compounds of $A^{\prime }{A}^{\prime \prime }B{X}_4$ fa…