Temperature-dependent dielectric functions and interband critical points of relaxor lead hafnate-modified PbSc_1/2Ta_1/2O₃ ferroelectric ceramics by spectroscopic ellipsometry

The electronic band structures and dielectric functions of (1-x)PbSc _1/2Ta_1/2O₃-xPbHfO₃ ceramics with different composition have been investigated by variable-temperature spectroscopic ellipsometry. Using the standard critical-point (SCP) model, three typical interband transitions can be observed from the second derivative of dielectric functions. The CP transitions, which are sensitive to B-site order degree, show a redshift trend with the temperature due to the electron-phonon interactions and lattice thermal expansion. The linear temperature coefficients are varied with oxygen vacancy, B-atom (Sc, Ta, Hf) arrangement, and Pb-O bonds owing to addition of PbHfO₃.