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The traditional BaTiO3/PbTiO3 ferroelectric material has excellent performance and is widely used, but the Pb in the material has polluted the environment. Studies have found that other ferroelectric materials can also have good performance after doping and improvement. The problem is that the development is too slow. If a reasonable explanation can be given for the changes from the original structure, the research and development process will be accelerated. In this paper, we investigated the ferroelectric properties at the orthogonal-crystal KNbO3 using first-principles calculations coupled with a phenomenological theory model. By replacing the K atoms with Na, studying the stability, polarization, energy band, and density of states after replacement doping, explaining the internal mechanism of its generation, and providing theoretical support for the research and development of new materials.

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The structure, electronic and ferroelectric properties of BSZT were investigated based on first-principles calculations. The result of relaxation structure and two-dimensional charge density indicates that the tetragonal crystalline structure is distorted after Sr and Zr doping. The double-well curve fits well with the phenomenological Landau-Devonshire theory. Moreover, the smaller Zr ion displacement leads to a lower spontaneous polarization of BSZT than the original BaTiO3. The hybridization between the 3d states of Ti and the 2p states of O, and the hybridization between the 4d states of Zr and the 2p states of O are observed in the density of states, which is the reason for the ferroelectricity of BSZT materials.