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The coexistence of ferroelectric ferroelastic domains in some materials plays an important role in practical area of domain engineering. Here the problem is discussed theoretically from the point of view of elastic aspects. Domain quadruplets are considered, i.e. systems of four ferroelastic domains coinciding along one intersection line. Conditions at which the elastic energy of quadruplets is zero are specified; they would allow for the existence of permissible quadruplets. The problem has been solved for the species m
m − P ϵds-mm2 representing KNbO3 crystals in which regular quadruplets have been discovered. It is concluded that such quadruplets are not permissible but can be formed when specific conditions for spontaneous strain are fulfilled. Theoretical results can be used to specify these conditions.
Acknowledgments
The work of one of the authors (J.F.) was sponsored by the Czech Grant Agency under Grant No. 202/02/1006 and by the Ministry of Education of Czech Republic under Research Program MSM 242200002. Part of this work was done within the framework of the Swiss National Research Program on Nano-Science (NCCR).
Paper originally presented at AMF-4, Bangalore, India, December 12-15, 2003.