Stability of the polar faces in KTiOPO4 crystalline layers grown by liquid phase epitaxy
The polar faces, (001) and (00), of the ferroelectric KTiOPO4 crystal are not equivalent by symmetry. The stability and the growth rate of both faces have been determined by growing thick crystalline layers by liquid phase epitaxy onto oriented crystalline commercial KTiOPO4 slabs. Growth solutions with different molar compositions in the system KTiOPO4–KPO3–KF and different supersaturation degrees end up with the same result. Whereas the (00) faces are stable under all the experimental conditions used, the (001) ones are not stable and turn into (00) faces. Head-to-head domains oriented along the  axis at |7 ± 1°| to the  axis propagate from the (001) surface of the seed to the as-grown crystalline layers. The final epitaxies obtained by this process show two (00) polar end faces; so a twin-crystal along the c direction was grown.