Lattice parameters and electronic bandgap of orthorhombic potassium sodium niobate K _0.5 Na _0.5 NbO _3 from density-functional theory

We perform a theoretical analysis of the structural and electronic properties of sodium potassium niobate K _1-x Na _x NbO _3 in the orthorhombic room-temperature phase, based on density-functional theory in combination with the supercell approach. Our results for x=0 and x=0.5 are in very good agreement with experimental measurements and establish that the lattice parameters decrease linearly with increasing Na contents, disproving earlier theoretical studies based on the virtual-crystal approximation that claimed a highly nonlinear behavior with a significant structural distortion and volume reduction in K _0.5 Na _0.5 NbO _3 compared to both end members of the solid solution. Furthermore, we find that the electronic bandgap varies very little between x=0 and x=0.5 , reflecting the small changes in the lattice parameters. Graphic abstract