Dipole patterns in the structures of some ferroelectrics and antiferroelectrics

4. Conclusion

The dipole patterns in the ferroelectric and antiferroelectric structures are drawn according to experimentally determined symmetry changes in the ferroelectrics and antiferroelectrics. For the ferroelectrics the dipoles of the unit cells for one domain are oriented in parallel and the directions of the polarisation in the adjacent domains are at definite angles to each other. It is assumed for the antiferroelectrics, that the superstructural unit cell is formed by the adjacent cells of the paraelectrical modification; the subcells having the antiparallel directions of the polarisation. It is these superstructural cells of the antiferroelectrics that are determined during the experimental investigations of the antiferroelectrics. The superstructural cells of the adjacent domains are different. In one case, the difference is that in the adjacent domains, the directions of the polarisation in the subcells form an angle (e.g., in PbZrO₃). In other cases the superstructural cells have not only different directions of the polarisation in the subcells but different signs of the enantiomorphism (e.g., NH₄H₂PO₄). In the third case, the only difference is that the superstructural unit cells in the adjacent domains are turned by an angle to each other round the direction of the subcell polarisation [e.g., (NH₄)₂H₃IO₆], etc.