Calculation of a phase diagram for $NH_4Br$

Özet

For $NH_4Br$, there exist three phases; the disordered $\beta$, antiferro-ordered $\gamma$ and ferro-ordered $\delta$ phases. In this study, we expand the free energy in powers of the order parameter to obtain the phase diagram for $NH_4Br$. This expansion has been made around the triple and the tricritical point for $NH_4Br$. Our phase line equations have then been fitted to the experimental data. This gives that our calculated phase diagrams describe adequately the observed behavior of $NH_4Br$.