Electronic band structures, dielectric functions and interband transitions of relaxor ferroelectric (1-x) Pb (Sc1/2Ta1/2) O3-xPbHfO3 ceramics: A spectroscopic reflectance study

Abstract

Electronic band structures and dielectric functions of relaxor ferroelectric (1-x) Pb (Sc1/2Ta1/2) O3-xPbHfO3 (PSTH) ceramics (0⩽x⩽0.2) have been investigated by far-IR–UV reflectance spectra. Based on generalized four-parameter damped oscillators and Tauc–Lorentz dispersion models, the dielectric functions from 0.006 to 6eV have been successfully extracted at room temperature. The status of structural order can be characterized by combining the strength of the Sc–Ta vibrational mode and the dielectric loss in the frequency range of 280–320cm−1. It was found that the electronic structures (which depend closely on the BO6 (B=Sc, Ta Hf) octahedron) are sensitive to the B-site atom concentration. The interband transitions can be clearly demonstrated by the imaginary part of the dielectric function which corresponds to the transition from the O 2p to B-site (Sc, Ta and Hf) d states and Pb 6p states. The two typical transition energies show the opposite trend with increased PbHfO3 composition. Remarkable variations of the B-site order degree and the lattice expansion due to the introduction of PbHfO3 are responsible for modifications of the dielectric function and electronic structures. These results could be crucial for investigating the potential applications of PSTH-based optoelectronic and pyroelectric devices.