Ferroelastic orientation states and domain walls in lead phosphate type crystals

The monoclinic structural distortion in lead phosphate and lead arsenate is correlated with the ferroelastic phase transition R (3) over bar m --> C2/ C and R (3) over bar m --> P2(1)/c respectively. The resulting domain patte rns in the mixed compounds depend on their chemical composition. The inters ection of ferroelastic W domain walls with the (100) surface of lead phosph ate-arsenate mixed crystals has been imaged using tapping mode atomic force microscopy. Dilution of the strain leads to characteristic surface deforma tions which deviate from those in pure lead phosphate. In highly twinned le ad phosphate-arsenate, X-ray diffraction (XRD) was used to show renormaliza tion effects and scattering phenomena stemming from the twin walls. The wal l trajectory was Found to be independent of chemical variations using trans mission electron microscopy.