Interband electronic transitions and phase transformation of multiferroic Bi{sub 1−x}La{sub x}Fe{sub 1−y}Ti{sub y}O{sub 3} ceramics revealed by temperature-dependent spectroscopic ellipsometry

Journal Article · Sat Dec 21 04:00:00 EST 2013 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4851795· OSTI ID:22266106

Xu, L. P.; Jiang, P. P.; Duan, Z. H.; Zhu, Z. Q.; Chu, J. H. ^[1]; Zhang, L. L.; Yu, J. ^[2]

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1. Key Laboratory of Polar Materials and Devices (MOE), Department of Electronic Engineering, East China Normal University, Shanghai 200241 (China)
2. Functional Material Research Laboratory, Tongji University, Shanghai 200092 (China)

Optical properties and phase transition of Bi{sub 1−x}La{sub x}Fe{sub 1−y}Ti{sub y}O{sub 3} (BLFTO) ceramics with different composition (0.02 ≤ x ≤ 0.10, 0.01 ≤ y ≤ 0.06) have been investigated by spectroscopic ellipsometry (SE) in the temperature range of −70–450 °C. The real part of the complex dielectric function ε{sub 1} increases with the temperature. Meanwhile, the imaginary part ε{sub 2} in the low-energy region decreases with the temperature and has an opposite trend in the high-energy side. Four typical interband transitions (E{sub a} ∼ 2.50 eV, E{sub b} ∼ 2.70 eV, E{sub c} ∼ 3.60 eV, and E{sub d} ∼ 4.25 eV) can be observed from the second derivative of the complex dielectric functions with aid of the standard critical point model. The critical point (CP) transition becomes broadening and shifts to a lower energy side as La and Ti compositions increase. Moreover, the CP transition energies show a red-shift trend with increasing the temperature until 320 °C, due to the lattice thermal expansion and electron-phonon interaction. The typical interband transitions and partial spectral weight present anomalies in the proximity of antiferromagnetic transition owing to the coupling between magnetic and ferroelectric order parameters and spin-lattice coupling for BLFTO multiferroic materials. It was found that the Néel temperature of BLFTO ceramics decreases from 364 to 349 °C with increasing doping composition of La and Ti elements. These phenomena can be attributed to the modification of electronic structure and magnetic order because the differences of electronegativity and ionic radii between Bi and La, Fe and Ti induce the variations on the bond angle and bond length between cations and anions. Moreover, the substitution for magnetic Fe{sup 3+} ions with nonmagnetic Ti{sup 4+} ions can reduce the exchange interaction between adjacent magnetic moments. Therefore, SE technique can be sensitive for detecting the phase/structural transitions of multiferroic oxides.

• OSTI ID: 22266106
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 23 Vol. 114; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANIONS
ANTIFERROMAGNETISM
BOND ANGLE
BOND LENGTHS
CATIONS
CERAMICS
ELECTRON-PHONON COUPLING
ELLIPSOMETRY
ENERGY-LEVEL TRANSITIONS
EXCHANGE INTERACTIONS
FERROELECTRIC MATERIALS
IRON IONS
OPTICAL PROPERTIES
ORDER PARAMETERS
OXIDES
PHASE TRANSFORMATIONS
TEMPERATURE DEPENDENCE
THERMAL EXPANSION
TITANIUM IONS