Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
On the example of (111) twins in cubic BaTiO3 it has been shown that reducing sintering conditions influence the propensity of the grains to twin, i.e. the formation of a hexagonal stacking sequence in a form of Ti2O9 coordination groups. Furthermore, Ti2O9 groups are a common for both (111) cubic twins and the hexagonal polymorph itself. In the literature, there is no experimental evidence that would explain the nature of cubic–hexagonal phase transformation mechanism. This phase transformation may be shifted far below the normal transition temperature when processing under reducing conditions. While Ti3+ ions stabilise the hexagonal stacking (either in twins or the hexagonal phase) at lower temperatures, they are no longer necessary close to a normal transition temperature. This observation suggests that (111) twins in BaTiO3 are preparatory stage of cubic–hexagonal phase transformation, where the phase transformation can be controlled by a suitable chemical environment that stimulates or prevents the formation of hexagonal stacking.