Electronic band structures, dielectric functions and interband transitions of relaxor ferroelectric (1-x) Pb (Sc_(1/2)Ta_(1/2))O_3-xPbHfO_3 ceramics: A spectroscopic reflectance study

摘要

Electronic band structures and dielectric functions of relaxor ferroelectric (1-x) Pb (Sc_(1/2)Ta_(1/2)) O_3-xPbHfO_3 (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 6 eV 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 280-320 cm~(-1). It was found that the electronic structures (which depend closely on the BO_6 (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 PbHfO_3 composition. Remarkable variations of the B-site order degree and the lattice expansion due to the introduction of PbHfO_3 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.