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Origin of the Anomalous Piezoelectric Response in Wurtzite Sc_xAl_{1-x}N Alloys

Ferenc Tasnádi, Björn Alling, Carina Höglund, Gunilla Wingqvist, Jens Birch, Lars Hultman, and Igor A. Abrikosov

                                                 

Phys. Rev. Lett. 104, 137601 (2010)

                                           

We present the theory that reveals the origin of the observed anomalous enhancement of piezoelectric response in wurtzite Sc_{x}Al_{1-x}N alloys. Our first-principles calculations confirm that the 400% increase of the piezoelectric constant is an intrinsic alloying effect. The energysurface topology is found to be strongly influenced by the alloying, being elongated around the global minimum along c=a direction. This leads to the large elastic softening along the crystal parameter c, and raises significantly the intrinsic sensitivity to axial strain resulting in the highly increased piezoelectric constant. The role of the local environment effects characteristic for disordered alloys is demonstrated. The preference of Sc atoms to bind rather hexahedrally than tetrahedrally to nitrogen results in a frustrated system with a strong response to strain. The effect is particularly accentuated at intermediate compositions where the elongated double-minimum energy landscape is flattened due to the energy proximity of the wurtzite and hexagonal phases of these alloys.


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Last updated: 10/21/10