Optical properties of manganese ferrites

Abstract

The near normal reflectance spectrum together with the data on the index of refraction and the extinction coefficient are combined in a Kramers-Kronig analysis to obtain the spectral dependences of the real and the imaginary parts of the diagonal elements of the dielectric function of the single crystal series Mn,Fes-,O, for 0 5 z 5 1.6. One-oscillator fit t o optical constants is used to show that the main rise in absorption at about 2 eV is due to the ad-crystal field transitions of the Fe3+ and/or Mn2+ ions in tetrahedral sites. The anomalous behaviour of optical constants below-1 eV in iron rich Mn-ferrites is ascribed to the presence of charge carriers (Fez+) in octahedral sites.Das bei fast normalem Lichteinfall gemessene Reflexionsspektrum wird zusammen mit den Werten des Brechungsindex und des Extinktionskoeffizienten fur die Kramers-Kronig-Analyse benutzt, um die SpektralabhLngigkeit der Real-und Imaginarteile der Diagonalelemente der Dielektrizitatsfunktion von Mn,Fes-,O,-Einkristallen (0 5 z 5 1,6) zu erhalten. Die Anpassung der optischen Konstanten an das Ein-Oszillator-Model1 zeigt, daB fur den Hauptanstieg der Absorption um etwa 2 eV die 3d-Kristallfeldiibergange der Fe3+-und/oder Mn2+-Kationen in den Tetraederplatzen verantwortlich sind. Das anomale Vehalten der optischen Konstanten unterhalb 1 eV in eisenreichen Manganferriten wird der Anwesenheit von Ladungstragern (Fez+) in Oktaederplatzen zugeschrieben.Na Slovance 2, 18040 Praha 8, Czechoslovakia. z, KotlGskiL 2, 61137 Brno, Czechoslovakia.

The Verwey transition - a topical review

“…(2) Optical properties. Attempts have been made to deduce additional information on the characteristics of the Verwey transition from investigations of the optical properties of Fe 3 O 4 like reflection, refraction, absorption (optical conductivity), dielectric constants, etc [106][107][108][109][110][111][112].…”

Extracting Optical Parameters of Cu–Mn–Fe Spinel Oxide Nanoparticles for Optimizing Air-Stable, High-Efficiency Solar Selective Coatings

“…First, the cross sections of scattering ( C sca ) and absorption ( C abs ) of spherical NPs with a given average size were calculated using Lorentz-Mie theory (Mieplot) based on the relative refractive index of NPs ( n 0 + ik 0 ) to that of the matrix material of the coating ( n m + ik m ). The complex refractive index of Mn 0.9 Fe 2.1 O 4 from ref is input as the initial n 0 + ik 0 , while n m + ik m of the silicone matrix is obtained by optical measurements . The absorption ( K ) and scattering ( S ) coefficients of the pigmented coating are calculated by K = C abs × f / V and S = C sca × f / V by taking into account the NP volume V and NP volume fraction f .…”

“…(2) The prominent anomalous sub-bandgap absorption in the near-infrared (NIR) regime of the solar spectrum is important to improve the solar selectivity, but the origin remains unclear in literature. Mechanisms range from charge transfer between bivalence-metal ions occupying distorted octahedral or tetrahedral sites − (e.g., in Mn x Fe 3– x O 4+γ single crystals) to Urbach tail absorption (e.g., in CuCoO x ) to chemical substitution and partially inverted configuration between tetrahedral A sites and octahedral B sites . Therefore, a more accurate understanding of the electronic transitions in spinel nanoparticles should be developed by studying and comparing more compounds of the same family.…”

“…(1) The fundamental optical parameters of spinel oxide NPs are largely unavailable. The data are only limited to some particular compositions in the form of single crystals or thin films. , Defects, cation inversion and substitution, and off-stoichiometry due to synthesis methods may further lead to a large deviation in the optical property of spinel NPs pigments (10–50 nm in diameter) from that of the bulk material. ,− Thus, it is important to develop a reliable method to derive wavelength-dependent effective absorption coefficient of the NPs from the measured optical spectra of the NP-pigmented composites. (2) The prominent anomalous sub-bandgap absorption in the near-infrared (NIR) regime of the solar spectrum is important to improve the solar selectivity, but the origin remains unclear in literature.…”

“…The data are only limited to some particular compositions in the form of single crystals or thin films. 22,23 Defects, cation inversion and substitution, and off-stoichiometry due to synthesis methods may further lead to a large deviation in the optical property of spinel NPs pigments (10−50 nm in diameter) from that of the bulk material. 22,24−26 Thus, it is important to develop a reliable method to derive wavelength-dependent effective absorption coefficient of the NPs from the measured optical spectra of the NP-pigmented composites.…”