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Title: First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution

Abstract

Theoretical calculations of Zn K and Fe K x-ray absorption near-edge structures (XANES) using a first-principles method have been performed to evaluate the degree of cation disordering in spinel zinc ferrite (ZnFe{sub 2}O{sub 4}) thin film prepared by a sputtering method, ZnFe{sub 2}O{sub 4} thin films annealed at elevated temperatures, and ZnFe{sub 2}O{sub 4} bulk specimen prepared by a solid-state reaction. Using the full-potential linearized augmented plane-wave + local orbitals method, a theoretical spectrum is generated for the tetrahedral and octahedral environments for each of the two cations. The experimental XANES spectrum of the thin film annealed at 800 deg. C as well as that of bulk specimen is successfully reproduced by using either the theoretical spectrum for Zn{sup 2+} on the tetrahedral site (A site) or that for Fe{sup 3+} on the octahedral site (B site), which is indicative of the normal spinel structure. For the as-deposited film, on the other hand, excellent agreement between theoretical and experimental spectra is obtained by considering the presence of either ion in both the A and B sites. The degree of cation disordering, x, defined as [Zn{sub 1-x}{sup 2+}Fe{sub x}{sup 3+}]{sub A}[Zn{sub x}{sup 2+}Fe{sub 2-x}{sup 3+}]{sub B}O{sub 4}, is estimated to bemore » approximately 0.6 in the as-deposited film, which is consistent with the analysis of the extended x-ray absorption fine structure on the Zn K edge. Curious magnetic properties as we previously observed for the as-deposited thin film--i.e., ferrimagnetic behaviors accompanied by large magnetization at room temperature and cluster spin-glass-like behavior--are discussed in connection with disordering of Zn{sup 2+} and Fe{sup 3+} ions in the spinel-type structure.« less

Authors:
; ; ;  [1];  [2];  [3]
  1. Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan)
  2. Department of Materials Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan)
  3. Department of Materials Science and Engineering, Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501 (Japan)
Publication Date:
OSTI Identifier:
20957836
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 17; Other Information: DOI: 10.1103/PhysRevB.75.174443; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; ANNEALING; ANTIFERROMAGNETIC MATERIALS; CATIONS; FERRITE; FERRITES; FINE STRUCTURE; IRON IONS; MAGNETIC PROPERTIES; MAGNETIZATION; SIMULATION; SPIN GLASS STATE; SPINELS; SPUTTERING; TEMPERATURE RANGE 0273-0400 K; THIN FILMS; X RADIATION; X-RAY SPECTROSCOPY; ZINC; ZINC IONS

Citation Formats

Nakashima, Seisuke, Fujita, Koji, Tanaka, Katsuhisa, Hirao, Kazuyuki, Yamamoto, Tomoyuki, and Tanaka, Isao. First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.174443.
Nakashima, Seisuke, Fujita, Koji, Tanaka, Katsuhisa, Hirao, Kazuyuki, Yamamoto, Tomoyuki, & Tanaka, Isao. First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution. United States. doi:10.1103/PHYSREVB.75.174443.
Nakashima, Seisuke, Fujita, Koji, Tanaka, Katsuhisa, Hirao, Kazuyuki, Yamamoto, Tomoyuki, and Tanaka, Isao. Tue . "First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution". United States. doi:10.1103/PHYSREVB.75.174443.
@article{osti_20957836,
title = {First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution},
author = {Nakashima, Seisuke and Fujita, Koji and Tanaka, Katsuhisa and Hirao, Kazuyuki and Yamamoto, Tomoyuki and Tanaka, Isao},
abstractNote = {Theoretical calculations of Zn K and Fe K x-ray absorption near-edge structures (XANES) using a first-principles method have been performed to evaluate the degree of cation disordering in spinel zinc ferrite (ZnFe{sub 2}O{sub 4}) thin film prepared by a sputtering method, ZnFe{sub 2}O{sub 4} thin films annealed at elevated temperatures, and ZnFe{sub 2}O{sub 4} bulk specimen prepared by a solid-state reaction. Using the full-potential linearized augmented plane-wave + local orbitals method, a theoretical spectrum is generated for the tetrahedral and octahedral environments for each of the two cations. The experimental XANES spectrum of the thin film annealed at 800 deg. C as well as that of bulk specimen is successfully reproduced by using either the theoretical spectrum for Zn{sup 2+} on the tetrahedral site (A site) or that for Fe{sup 3+} on the octahedral site (B site), which is indicative of the normal spinel structure. For the as-deposited film, on the other hand, excellent agreement between theoretical and experimental spectra is obtained by considering the presence of either ion in both the A and B sites. The degree of cation disordering, x, defined as [Zn{sub 1-x}{sup 2+}Fe{sub x}{sup 3+}]{sub A}[Zn{sub x}{sup 2+}Fe{sub 2-x}{sup 3+}]{sub B}O{sub 4}, is estimated to be approximately 0.6 in the as-deposited film, which is consistent with the analysis of the extended x-ray absorption fine structure on the Zn K edge. Curious magnetic properties as we previously observed for the as-deposited thin film--i.e., ferrimagnetic behaviors accompanied by large magnetization at room temperature and cluster spin-glass-like behavior--are discussed in connection with disordering of Zn{sup 2+} and Fe{sup 3+} ions in the spinel-type structure.},
doi = {10.1103/PHYSREVB.75.174443},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 17,
volume = 75,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • Using a first-principles band-structure method, we have systematically studied the cation distribution in closed-shell A{sup II}B{sub 2}{sup III}O{sub 4} and A{sup IV}B{sub 2}{sup II}O{sub 4} spinels where the group-II atoms are Mg, Zn, and Cd, the group-III atoms are Al, Ga, and In, and the group-IV atoms are Si, Ge, and Sn. The total energies, the structural parameters, and the band gaps of these compounds in both normal and inverse spinel structures are calculated. Compared with previous model studies, we show that an atomistic method is crucial to correctly identify the stability of the spinels and to calculate the anionmore » displacement parameter u. The preference of cations with delocalized valence d states (e.g., Zn) to form covalent tetrahedral bonds also plays a significant role in determining the cation distribution in the spinels. Furthermore, the electronic structures of these spinel compounds depend strongly on the cation distribution. For most of the spinels studied here, the calculated band gaps for the inverse spinels are smaller than the corresponding normal spinels except for SnB{sub 2}{sup II}O{sub 4}.« less
  • The Co{sub 2.25}Fe{sub 0.75}O{sub 4} ferrite composition has been prepared by chemical co-precipitation route. The as-prepared sample after annealing at 900°C in air formed single phase cubic spinel structure. Synchrotron X-ray diffraction and X-ray absorption near edge structure (XANES) measurements were used to study charge states of the cations in octahedral and tetrahedral sites of the cubic spinel structure. Raman spectra indicated normal cubic spinel structure. XANES data suggested the existence of Fe{sup 4+} ions in the spinel structure.
  • Immiscibility in the trevorite (NiFe{sub 2}O{sub 4}) - franklinite (ZnFe{sub 2}O{sub 4}) spinel binary is investigated by reacting 1:1:2 molar ratio mixtures of NiO, ZnO and Fe{sub 2}O{sub 3} in a molten salt solvent at temperatures in the range 400-1000 C. Single phase stability is demonstrated down to about 730 C (the estimated consolute solution temperature, T{sub cs}). A miscibility gap/solvus exists below Tcs. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n - values = 0.15, 0.8 at 300 C. A thermodynamic analysis, which accounts for changes in configurational and magnetic ordering entropies during cation mixing,more » predicts solvus phase compositions at room temperature in reasonable agreement with those determined by extrapolation of experimental results. The delay between disappearance of magnetic ordering above T{sub C} = 590 C (for NiFe{sub 2}O{sub 4}) and disappearance of a miscibility gap at T{sub cs} is explained by the persistence of long-range ordering correlations in a quasi-paramagnetic region above T{sub C}.« less
  • The cation site occupancy of a mechanically activated nanocrystalline zinc ferrite powder was determined as (Zn{sub 0.55}{sup 2+}Fe{sub 0.18}{sup 3+}){sub tet}[Zr{sub 0.45}{sup 2+}Fe{sub 1.82}{sup 3+}]{sub oct}O{sub 4} through analysis of extended x-ray absorption fine structure measurements, showing a large redistribution of cations between sites compared to normal zinc ferrite samples. The overpopulation of cations in the octahedral sites was attributed to the ascendance in importance of the ionic radii over the crystal energy and bonding coordination in determining which interstitial sites are occupied in this structurally disordered powder. Slight changes are observed in the local atomic environment about the zincmore » cations, but not the iron cations, with respect to the spinel structure. The presence of Fe{sup 3+} on both sites is consistent with the measured room temperature magnetic properties. (c) 2000 American Institute of Physics.« less