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A Landau–Devonshire thermodynamic energy density function for ferroelectric wurtzite aluminum scandium nitride (Al1−xScxN) solid solution is developed. It is parametrized using available experimental and theoretical data, enabling the accurate reproduction of composition-dependent ferroelectric properties, such as spontaneous polarization, dielectric permittivity, and piezoelectric constants, for both bulk and thin films. The maximum concentration of Sc for the wurtzite structure to remain ferroelectric is found to be 61 at. %. A detailed analysis of Al1−xScxN thin films reveals that the ferroelectric phase transition and properties are insensitive to substrate strain. This study lays the foundation for quantitative modeling of novel ferroelectric wurtzite solid solutions. [ABSTRACT FROM AUTHOR]

The energy conversion potential of ferroelectric materials originating from their phase transitions, in particular temperature ranges and electric field values, is very promising. Pyroelectric energy harvesting consists of directly converting thermal energy into electrical energy. Due to its high energy conversion potential, the Olsen cycle is the most favorable for pyroelectric energy harvesting. This cycle includes two isothermal and two constant electric field branches. In this study, the Olsen cycle was modeled, then varying temperatures and applied electric field directions for different crystal orientations were simulated. Polarization responses were obtained via the Landau–Devonshire theory. Then, an innovative way to model the electrocaloric effect was proposed; experimental results and first-principle calculations confirmed the simulation results. The resulting negative electrocaloric effect due to crystal orientation, previously reported in the literature, has been successfully simulated through a phenomenological approach. Finally, we identified which phase transitions are interesting for pyroelectric energy harvesting applications depending on crystal orientations while obtaining an energy density in the order of ≈ 10 2 mJ / cm 3. This value corresponds to previous results in the literature. [ABSTRACT FROM AUTHOR]

The topologically protected vortex–antivortex (V–AV) domain structure in ferroelectric hexagonal manganites has been highly concerned recently, but its stability against intrinsic defects remains to be understood, given the claim that a topological structure would be robust against defects and other perturbations. In fact, it is also known that the V–AV structure is sensitive to the sample quality, and such a well-developed structure is hardly observed in thin films and defective single crystals. In this work, we investigate the influence of anti-trimer point defects on the stability of the V–AV domain structure by employing the phase-field simulation based on the Landau–Devonshire phenomenological theory. It is revealed that the characteristic V–AV structure essentially relies on the anti-trimer point defects under consideration. These defects lower the trimerization transition temperature on one hand and produce pinning effect on the vortex cores/walls on the other hand. However, the V–AV structure does remain robust if the anti-trimer magnitude of these defects is relatively weak but will be eventually destroyed if the anti-trimer magnitude is strong. [ABSTRACT FROM AUTHOR]