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 [010] axis at |7 ± 1°| to the [001] 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.