Lattice dynamics and electronic structures of SrFeO3-δ single crystals
P. C. Chun (鍾佩君)1*, H. L. Liu (劉祥麟)1, and C. H. Du (杜昭宏)2
1Department of Physics, National Taiwan Normal University, Taipei, Taiwan
2Department of Physics, Tamkang University, New Taipei City, Taiwan
* presenting author:佩君鍾,
Raman scattering and spectroscopic ellipsometry were used to investigate the lattice dynamics and electronic structures of SrFeO3-δsingle crystals. These materials are interesting on account of their complex magnetic phase transitions. At room temperature, Raman-scattering spectrum of SrFeO2.86 shows fourteen phonon modes at about 83, 94 107, 123, 135, 175, 226, 320, 332, 414, 428, 479, 626 and 1363 cm-1. The phonon eigenfrequencies of SrFeO2.75 are close to those of SrFeO2.86, but the disappearance of one feature at about 226 cm-1. With decreasing temperature, the phonon parameters are not affected by the onset of magnetic ordering. Furthermore, the absorption spectra determined from spectroscopic ellipsometry analysis of SrFeO3-δ exhibit three maxima in the spectral range from 1.8 — 5.1 eV. The optical absorption near 1.8 eV is due to on-site Fe4+ d-d excitations. Other high energy peaks above 2 eV are associated with the charge-transfer transitions between O 2p and Fe 3d states. 

Keywords: Raman scattering, SrFeO