Plate-shaped untwinned and twinned single crystals of the perovskite BiFeO ₃ show different etch figures and etch figure arrangements on the surface when attacked with dilute nitric acid. These etch figures can be correlated with the orientation of the spontaneous polarization vector. With a view to correlating the direction of the polarization vector with the atomic positions in the crystal, the absolute configuration was determined from X-ray diffraction patterns at room temperature on a dendritic ferroelastic/ferroelectric asgrown single domain crystal. The typical etch figure arrangement close to the crystal edges was used as a reference system. The absolute structure shows that the part of the crystal corresponding to the positive end of the spontaneous polarization vector etches faster than the negative one.

The structure refinement of a single crystal switched by uniaxial stress along the polar axis showed a complete reorientation of the (super)structure with rearrangement to an angle of 70.5° compared with the former polarization direction. As already suggested by the analysis of new etch figures close to 45°-inclined domain walls, no merohedral twinning occurs during this rearrangement. Despite atom displacements from 0.4 Å (for Fe) and 0.9 Å (for O) the crystal does not break during switching.