First principles calculations are done for a $\sqrt{2}\times 4\times 2\sqrt{2} Pnma$ structure, which has been recently discussed in several attempts to describe experiments in complex magnetoelectric perovskites and which experimentally was shown to compete with several ferroelectric phases. This makes these materials extremely attracting as switchers, starters, field-stimulated capacitors, high-voltage converters, transmitters, etc. The relative energies of the $\sqrt{2}\times 4\times 2\sqrt{2} Pnma$ structure have been calculated from first principles and analyzed as a function of pressure in ${\mathrm{BiFeO}}_3$. The stability of two polymorphs of the $\sqrt{2}\times 4\times 2\sqrt{2} Pnma$ structure has been studied for solid solution ${\mathrm{BiFe}}_{1/2}{\mathrm{Sc}}_{1/2}{\mathrm{O}}_3$. The main distortions and relative energies of these two polymorphs in ${\mathrm{BiFe}}_{1/2}{\mathrm{Sc}}_{1/2}{\mathrm{O}}_3$, in terms of $Pm\overline{3}m$ parent symmetry, have been calculated from first principles as well.

• Received 23 April 2014
• Revised 24 July 2014

DOI:https://doi.org/10.1103/PhysRevB.90.054110