parameters $\psi_1$ through $\psi_3$, one might expect that ordered domains grow according to the Lifshitz–Allen–Cahn law $l(t) \propto t^{\nu}$ with $\nu=1/2$.[@Lifsh; @AllenC] Experiments on Cu$_3$Au indeed were interpreted in terms of this conventional growth law.[@Shan; @Noda; @Konishi] In this context, however, one should be aware of the fact that systems of the type considered may show effective growth exponents during relaxation different from the Lifshitz–Allen–Cahn law. In the case of a vacancy mechanism effective exponents $\nu>1/2$ in principle can arise in models based on a non–conserved order parameter. In these studies,[@Vives; @Fratzl] an increased $\nu$ was ascribed to an accumulation of vacancies within the domain boundaries, leading to an enhancement of the interfacial dynamics. For the present model we have verified, however, that the interaction parameters chosen do not favor segregation of vacancies in the domain boundaries.[@Porta] Another modification of the Lifshitz–Allen–Cahn law that can act in the opposite direction results from local changes in composition within antiphase boundaries so that the ordering process gets coupled to a (slow) conserved order parameter component.

In our simulations we systematically observe effective growth exponents $\nu \simeq 1/4$ or even smaller (cf. Fig. 5 and Kessler [*et al.*]{} [@paper1]). Moreover, within our accessible 