Structural transition from vacancy-ordered tetragonal perovskite to tetragonal potassium tungsten bronze by the example of Na4Bi2Nb10O30

The phenomenological transition from the perovskite structure type to the potassium tungsten bronze structure type is considered. The structural motif of vacancy-ordered tetragonal perovskite (VOTP) with the space group P4/m is constructed. The atomic coordinates in the unit cell of VOTP and the Madelung energies for the unit cells of VOTP and tetragonal potassium tungsten bronze are calculated. The transition is experimentally observed in Na₄Bi₂Nb₁₀O₃₀ prepared by the solid-state reaction method. The X-ray diffraction pattern measured after the first annealing showed good agreement with the theoretical X-ray diffraction pattern calculated for VOTP Na₄Bi₂Nb₁₀O₃₀.