Changes in the electronic structure of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>BaTiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> due to ferroelectric phase transition investigated via polarization-dependent har

This study explored the changes in the electronic structure due to ferroelectric phase transition behavior of ${\mathrm{BaTiO}}_{3}$. The temperature variations in the electronic structure of a ferroelectric ${\mathrm{BaTiO}}_{3}$ crystal were investigated via hard x-ray photoemission spectroscopy (HAXPES) using linearly polarized x rays and density functional theory calculations. The observed valence band HAXPES spectra exhibited distinct temperature-dependent shapes owing to the crystalline phase transitions from a high-temperature paraelectric cubic phase to low-temperature ferroelectric phases with tetragonal, orthorhombic, and rhombohedral symmetries. The changes in the valence band spectra agreed with the simulated HAXPES spectra derived from the projected densities of states in the crystalline phases multiplied by the photoionization cross sections. This result suggests that the ferroelectric mechanism in ${\mathrm{BaTiO}}_{3}$ is of the displacive type, which involves structural phase transformations.