IMF2017

Unique properties of piezoelectric materials in generating electrical voltage suggested to mechanical strain (and vice versa) grants the piezoelectric utilization over a wide range of applications. In general, superior piezoelectricity usually occurs at morphotropic phase boundary (MPB) of the considered compounds. However, to synthesis materials having compositions lying this MPB is not trivial. This work therefore theoretically concentrated on pursing how to arrive in MPB of some promising piezoelectric materials using density functional theory (DFT). DFT with plane-wave pseudopotential method was employed for the calculation. xKNbO₃−(1-x)NaNbO₃(KNN) with known MPB composition of x = 0.5 was used to validate the calculation. Then, AgNbO₃-based compounds, which inherits large polarization and high piezoelectric performance such as xAgNbO₃-(1-x)KNbO₃(ANKN), xAgNbO₃-(1-x)BaTiO₃(ANBT), and xAgNbO₃−(1-x)SrTiO₃(ANST), were chosen in this MPB compositional investigation. Form the results, MPB composition of KNN of x = 0.5 was computationally suggested, implying our calculation method for MPB is reliable. Further results indicate that ANKN exhibits structural phase transition between Bmm2 and Pbma crystal symmetry at x ≈ 0.2 and 0.8. Also, there occur two MPB compositions at x = 0.125 and 0.5 for ANBT (with phase transition between P4mm and Pbma), but no MPB for ANST. In addition, ANBT with x ≈ 0.5 displays large polarization of about 44 μC/cm², suggesting ANBT-based compound a potential piezoelectric material for further development of piezoelectric-based device.