In this work we study, by means of ab initio calculations, the structural, electronic and magnetic properties of Y-doped BiFeO₃ compounds. We determine that there is a morphotropic phase boundary at an yttrium concentration of (18±2)%, where the structure changes from R3c to Pnma. This structural transition is driven by the chemical pressure induced by the dopant.

By analyzing the evolution of the oxygen octahedral tilts we find an enhanced antiferrodistortive distortion when increasing the Y-doping, together with a reduction of the ferroelectric distorsion, that gives rise to a smaller value of the electric polarization. These cooperative effects should lead to a larger canting of the Fe magnetic moments and to a larger ferromagnetic response in the R3c phase, as it is observed in the experiments.