First-principles calculations of electrical properties, structure, and phase transition of K_{1-: X}Na_xNbO₃ solid solutions

The structure, total energy and orthorhombic as well as tetragonal electronic properties of K_1-xNa_xNbO₃ (KNN) as a function of Na concentration were studied with first principles calculations. When the Na content of KNN was gradually increased the orthogonal phase transformation occurred, which produced an enhanced piezoelectric response of the tetragonal KNN. This result proved that the high d₃₃ originated from the phase transition. The corresponding calculations reveal that the change of Nb-O bond length is the origin of distortion of Nb-O octahedral and phase transition. In addition, the calculations observed an unusual high peak of the KNN piezoelectric parameter, which showed the same trend as the experimental results.