Structural study of KxNa1 − xNbO3 (KNN) for compositions in the range x = 0.24-0.36

The structure of the A‐site substituted perovskite KxNa1 − xNbO3, x = 0.24–0.36, where a phase boundary was previously reported, has been determined by high‐resolution X‐ray powder and neutron powder diffraction studies. The structure of the x = 0.3 compound was refined in the monoclinic space group Pm at 293 K and in P4mm at 523 K. The Glazer tilt system of the room‐temperature monoclinic phase is a0b+c0, which has implications for the nature of the next symmetry change with composition towards pure potassium niobate. A phase‐coexistence region at the transition between monoclinic and tetragonal phases was also identified, consistent with a first‐order phase boundary. There is also evidence for an intermediate oxygen‐octahedra tilted tetragonal phase.