For the scalar phi ⁴-lattice model of structural phase transitions the freezing transition at a temperature T_c* above T_c is found in the framework of mode-coupling theory. To study the critical behaviour of this transition the frequency and temperature dependencies of the linear and quadratic dynamical susceptibility are investigated by using a self-consistent numerical solution of the mode-coupling equations. Two cases are considered: (i) a pure crystalline system with a B transition at T_c*, and (ii) a system with randomly distributed defects with an A transition at T_c*. The experimental aspects of the presented results are discussed.