Significant Enhancement of Piezoelectric Response in AlN by Yb Addition

This study employs first-principles calculations to investigate how introducing Yb into aluminum nitride (AlN) leads to a large enhancement in the material’s piezoelectric response (d(33)). The maximum d(33) is calculated to be over 100 pC/N, which is 20 times higher than that of AlN. One reason for such a significant improvement in d(33) is the elastic-softening effect, which is indicated by a decrease in the elastic constant, C(33). The strain sensitivity (du/dε) of the internal parameter, u, is also an important factor for improving the piezoelectric stress constant, e(33). On the basis of mixing enthalpy calculations, Yb(x)Al(1−x)N is predicted to be more stable as a wurtzite phase than as a rock salt phase at composition up to x ≈ 0.7. These results suggest that Yb can be doped into AlN at high concentrations. It was also observed that the dielectric constant, [Formula: see text] , generally increases with increasing Yb concentrations. However, the electromechanical coupling coefficient, [Formula: see text] , only increases up to x = 0.778, which is likely because of the relatively lower values of [Formula: see text] within this range.