Electronic structures and abnormal phonon behaviors of cobalt-modified Na0.5Bi0.5TiO3-6%BaTiO3 single crystals
T. Huang,
P. Zhang,
L. P. Xu,
C. Chen,
J. Z. Zhang,
Z. G. Hu,
H. S. Luo,
J. H. Chu
Affiliations
T. Huang
Technical Center for Multifunctional Magneto-Optical Spectroscopy (ECNU), Shanghai, China and Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
P. Zhang
Technical Center for Multifunctional Magneto-Optical Spectroscopy (ECNU), Shanghai, China and Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
L. P. Xu
Technical Center for Multifunctional Magneto-Optical Spectroscopy (ECNU), Shanghai, China and Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
C. Chen
Jiangxi Key Laboratory of Advanced Ceramic Materials, Department of Materials Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333001, China
J. Z. Zhang
Technical Center for Multifunctional Magneto-Optical Spectroscopy (ECNU), Shanghai, China and Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
Z. G. Hu
Technical Center for Multifunctional Magneto-Optical Spectroscopy (ECNU), Shanghai, China and Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
H. S. Luo
R&D Center of Synthetic Crystals, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800, China
J. H. Chu
Technical Center for Multifunctional Magneto-Optical Spectroscopy (ECNU), Shanghai, China and Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
Optical properties, electronic structures, and structural variations of x wt% cobalt (Co) doped Na0.5Bi0.5TiO3-6%BaTiO3 (x=0%, 0.5%, 0.8%) single crystals have been studied by temperature-dependent optical ellipsometry and Raman spectra from 250 to 650 K. Based on the temperature evolution of electronic transitions (Ecp1 and Ecp2) and the phonon modes involving Ti-O vibrations, two critical temperature points exhibit an increasing trend with Co dopants, which are related to structural variations for ferroelectric to anti-ferroelectric, and anti-ferroelectric to paraelectric transition, respectively. Additionally, distinguishing abnormal phonon behaviors can be observed from Raman spectra for the crystal of x=0.5% and 0.8%, which show reverse frequency shift of the modes involving Ti-O vibration. It can be ascribed to different relative concentration of Co2+ and Co3+ in the crystals, which has been confirmed by X-ray Photoelectron Spectroscopy data.
