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Materials Science and Engineering Faculty Research & Creative Works

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Full-Text Articles in Chemistry

Structural And Magnetic Properties Of La Mn₁₋ₓfeₓo₃ (0 < X < 1.0), X.-D. Zhou, L. R. Pederson, Qingsheng Cai, Jinbo Yang, B. J. Scarfino, M. Kim, William B. Yelon, William Joseph James, Harlan U. Anderson, C. Wang Apr 2006

Structural And Magnetic Properties Of La Mn₁₋ₓfeₓo₃ (0 < X < 1.0), X.-D. Zhou, L. R. Pederson, Qingsheng Cai, Jinbo Yang, B. J. Scarfino, M. Kim, William B. Yelon, William Joseph James, Harlan U. Anderson, C. Wang

Materials Science and Engineering Faculty Research & Creative Works

Electronic, structural, and magnetic properties of Mn-doped lanthanum ferrites were studied by neutron diffraction, superconducting quantum interference device, and impedance spectroscopy. Neutron diffraction refinements were performed with the constraint of full La occupancy, which showed the presence of excess oxygen when x < 0.4. Mixed valent Mn cations and cation vacancies, therefore, exist in all the samples. The samples with x > 0.7 are magnetically ordered at room temperature with orthorhombic symmetry (Pbnm). When x < 0.3 the structure is rhombohedral and magnetically disordered above 16 K. The majority carriers, electron holes, correspond to high oxidation states of Mn. The carrier concentration is determined from the Seebeck coefficients, and is a function of temperature and Fe concentration. The measurements of conductivity and Seebeck coefficients show polaron hopping at elevated temperatures.

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Crystal And Electronic Structures Of Linh₂, Jinbo Yang, X.-D. Zhou, Qingsheng Cai, William Joseph James, William B. Yelon Jan 2006

Crystal And Electronic Structures Of Linh₂, Jinbo Yang, X.-D. Zhou, Qingsheng Cai, William Joseph James, William B. Yelon

Materials Science and Engineering Faculty Research & Creative Works

The crystal structure of LiNH2 was reinvestigated using powder neutron diffraction with high sensitivity. The compound crystallizes in the tetragonal space group I4 with lattice parameters α = b= 5.034 42 (24) Å, c = 10.255 58 (52) Å. It is found that H atoms occupy 8g1(0.2429, 0.1285, 0.1910) and 8g2 (0.3840, 0.3512, 0.1278) sites. The bond lengths between the nearest nitrogen and hydrogen atoms are 0.986 and 0.942 Å, respectively. The bond angle between H-N-H is about 99.97°. These results are significantly different from those of previous experiments. The electronic structure was calculated according to the revised structural …

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Coupled Electrical And Magnetic Properties In (La,Sr)Feo3-Δ, X.-D. Zhou, Qingsheng Cai, Jinbo Yang, M. S. Kim, William B. Yelon, William Joseph James, Y.-W. Shin, B. J. Scarfino, Harlan U. Anderson Jan 2005

Coupled Electrical And Magnetic Properties In (La,Sr)Feo3-Δ, X.-D. Zhou, Qingsheng Cai, Jinbo Yang, M. S. Kim, William B. Yelon, William Joseph James, Y.-W. Shin, B. J. Scarfino, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

This article is aimed at studying the temperature dependence oxygen nonstoichiometry, magnetic moments, Fe3+ fraction, Néel temperature and conductivity of (La,Sr)FeO3-δ. It is found that the magnetic properties in La0.60 Sr0.40 Fe3-δ is determined by Fe3+ and its concentration, and the conductance is resulted from Fe4+ ions, which act as electron holes. Both of magnetic and electrical properties were directly governed by oxygen nonstoichiometry (δ). when δ=0.2, the compound has maximum Fe3+, the saturation magnetic moments and Néel temperature are 3.8 µB and 410 °C, both at the highest level, …

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Study Of The Electronic Structure Of Cafeo₃, Jinbo Yang, M. S. Kim, Qingsheng Cai, X.-D. Zhou, Harlan U. Anderson, William Joseph James, William B. Yelon Jan 2005

Study Of The Electronic Structure Of Cafeo₃, Jinbo Yang, M. S. Kim, Qingsheng Cai, X.-D. Zhou, Harlan U. Anderson, William Joseph James, William B. Yelon

Materials Science and Engineering Faculty Research & Creative Works

We have studied the charge disproportionation phenomenon in CaFeO3 using the local-spin density approximation with the on-site Coulomb interaction parameter U and exchange parameter J. The calculation reveals that the total number of the 3d electrons is about 5.1 for both Fe(1)(Fe5+) and Fe(2)(Fe3+) atoms, and that there are about 0.25 electron holes in the O-2p band. Therefore, the charge disproportionation can be more accurately described as 2d5L(Fe4+)=d5L2(Fe5+)+d5(Fe3+), where L denotes a hole in the oxygen 2p band, instead of 2d4(Fe4+)=d3(Fe5+)+d5(Fe3+). The hybridization between the Fe-3d and O-2p orbitals is stronger for Fe(1) than for Fe(2) due to the shorter …

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Structure, Magnetic, And Transport Properties Of Ti-Substituted La₀.₇Sr₀.₃Mno₃, M. S. Kim, Jinbo Yang, Qingsheng Cai, X.-D. Zhou, William Joseph James, William B. Yelon, D. Buddhikot, Satish K. Malik, Paul Ernest Parris Jan 2005

Structure, Magnetic, And Transport Properties Of Ti-Substituted La₀.₇Sr₀.₃Mno₃, M. S. Kim, Jinbo Yang, Qingsheng Cai, X.-D. Zhou, William Joseph James, William B. Yelon, D. Buddhikot, Satish K. Malik, Paul Ernest Parris

Materials Science and Engineering Faculty Research & Creative Works

Ti-substituted perovskites La0.7Sr0.3Mn1-xTixO3 with 0 ≤ x ≤ 0.20, were investigated by neutron diffraction, magnetization, electric resistivity, and magnetoresistance (MR) measurements. All samples show a rhombohedral structure (space group R3c) from 10 K to room temperature. At room temperature, the cell parameters a,c and the unit cell volume increase with increasing Ti content. However, at 10 K, the cell parameter a has a maximum value for x = 0.10, and decreases for x > 0.10, while the unit cell volume remains nearly constant for x > 0.10. The average (Mn,Ti)-O bond length increases …

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Preparation Of Phase Homogeneous Mn-Zn Ferrite Powder By Spray Pyrolysis, Xinyu Zhao, Baicun Zheng, Hongchen Gu, Chunzhong Li, Shi C. Zhang, P. D. Ownby Jan 1999

Preparation Of Phase Homogeneous Mn-Zn Ferrite Powder By Spray Pyrolysis, Xinyu Zhao, Baicun Zheng, Hongchen Gu, Chunzhong Li, Shi C. Zhang, P. D. Ownby

Materials Science and Engineering Faculty Research & Creative Works

Two kinds of aqueous precursor solutions are used to synthesize Mn-Zn ferrite powders: (i) nitrate (NO) precursor-derived from solutions of Mn(NO3)2, Zn(NO3)2, and Fe(NO3)3; and (ii) acetate (AC) precursor-derived from solutions of Mn(CH3COOO)2, Zn(CHCH3COOO)2, and Fe(NO3)3. The composition of the powders synthesized from the precursor AC is very uniform, whereas powders derived from the precursor NO have Mn and Zn segregated on the particle surfaces. In addition, the powders synthesized from precursor AC are solid spherical …

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