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Detailed Program
Paper Number : CO-I02
Time Frame : 16:55~17:20
Presentation Date : Friday, 28, November
Session Name : Computational Ceramic Science and Engineering
Session Chair 1# : Seungwu Han
Session Chair 2# : Nakeshi Nishimatsu
First-Principles Study of Piezoelectricity in AlN-based Materials
Hiroyoshi MOMIDA
Osaka University
Piezoelectric materials are now used in numerous ways such as sensors, actuators, and filters in modern electronic devices. In the recent industrial applications, one of the widely used materials is metal oxide ceramics such as lead zirconium titanium oxides which has high piezoelectric constants of about 410 pC/N at temperatures up to about 250¡ÆC, and there are growing demands for novel materials that are usable in higher temperature environments such as in automobile engines. AlN is a candidate material for the high temperature applications due to its high Curie temperature of about 1150¡ÆC, and recently significant enhancement of piezoelectricity by alloying with Sc has been found experimentally, attracting great interest in technological as well as scientific fields [1].
In the context of such background, we have computationally investigated atomic mechanisms of the piezoelectricity enhancement of ScxAl1-xN materials, and our major goal is to provide a guiding principle to design highly piezoelectric materials by using first-principles calculations. AlN is known to have the wurtzite crystal structure, and we generate several ScxAl1-xN model structures by substituting Al with Sc for wide composition range of x=0–1. The first-principles calculations are based on the density functional theory within the generalized gradient approximation, and quantitatively reliable calculations of piezoelectric properties are possible on the basis of the Berry phase approach.
Figure 1 shows calculated piezoelectric constants of ScxAl1-xN models versus Sc concentrations. The calculated result clearly demonstrates that the piezoelectric responses of ScxAl1-xN increase with increasing Sc concentration (x), as reported by the experiments [1] and calculations [2]. Calculated piezoelectric constants are scattered especially in higher x, and this is due to different spatial distributions of Sc atoms in the models. We analyze microscopic origins of the enhanced piezoelectricity by Sc in AlN, and find that the positions of atoms around Sc largely change in response to external strains. We further carry out similar study for Y and La doped in AlN to examine an element dependence on piezoelectricity, though they are found to be less effective than Sc, probably due to their larger atomic sizes. We discuss a general trend of piezoelectricity versus structure parameters on the basis of our results for several materials with the wurtzite structure.

Figure 1 Calculated piezoelectric constants (d33) of ScxAl1-xN models vs. Sc concentration (x).

References:

[1] A. Teshigahara et al., Proc. of Ultrasonics Symposium (IUS), 2012 IEEE International (2012); M. Akiyama et al., Adv. Mater. 21 (2009) 593.
[2] F. Tasnádi et al., Phys. Rev. Lett. 104 (2010) 137601.
Acknowledgements :