4.2.2 Single Crystals - Polycrystals

As can easily be deduced from the introduction of the ferroelectric properties, presented in Chapter 2, single crystals are anisotropic. Depending on the number and location of the energy minima in the lattice, there are either one or two axes of anisotropy. The schematic overview of these states is given in Fig. 4.2 and Fig. 4.3 for a material with two axes of anisotropy.

Figure 4.2: Location of the center ion, first axis of anisotropy

Figure 4.3: Location of the center ion, second axis of anisotropy

If the size of the single crystals is small compared to the dimensions of the device and their orientation is random, the material will lose its anisotropic properties. Of course this case can be simulated by a setup consisting of several anisotropic single crystals, but one should keep in mind that the obtained results will be valid just for this unique configuration which might or might not be representative. In this case an approach that does not depend on the direction is quite useful. In order to keep the generic approach of the simulator, models for both of these cases were developed.