Processing and properties of pure antiferromagnetic h-YMnO3

Yttrium manganite (YMnO3) is widely investigated multiferroic material with potential use in many technological applications. In this paper, we report on the preparation and characterization of multiferroic hexagonal YMnO3 ceramics obtained by chemical synthesis route. Precursor powders were prepared by the polymerizable complex method from citrate precursors. After calcination at 900?C the powders contained mixture of Y-Mn-O phases which were further sintered at different temperatures. XRD analysis revealed that sintering at 1400?C resulted in the formation of pure hexagonal YMnO3. Density of the obtained ceramics was 96%TD. The ceramic samples proved to have multiferroic properties - they are antiferromagnetic below 42K with linear dependence of magnetization as a function of applied magnetic field. The ferroelectric measurements performed at room temperature showed remanent polarization of 0.21 ?C/cm2 and the coercive field of 6.0 kV/cm for the YMnO3 sample sintered at 1400?C. The magnetization curves measured at 2 and 5 K for the powder samples calcined at 900?C and ceramic samples sintered at 1300?C exhibited a hysteresis loop due to a small concentration of Mn3O4 in the samples.

The strongly defective double perovskite Sr11Mo4O23: crystal structure in relation to ionic conductivity

The crystal structure and ionic conductivity properties of a novel microcrystalline Sr11Mo4O23ceramic material are presented. This material has been prepared by thermal treatment up to 1473 K, in air, of previously decomposed citrate precursors. The complex crystal structure was refined from combined X-ray powder diffraction and neutron powder diffraction data. The formula of this phase can be rewritten as Sr1.75□0.25SrMoO5.75, highlighting the relationship with double perovskitesA2B′B′′O6. At room temperature, the crystal structure is tetragonal in space groupI41/a, witha= 11.6107 (6) Å,c= 16.422 (1) Å andV = 2213.8 (2) Å3. The crystal network contains O anion and Sr cation vacancies. The structure is complex, with Sr, Mo and O atoms distributed over four, two and six distinct Wyckoff sites, respectively. Only one of the Sr sites (SrO6) corresponds to the octahedral network; one of the two MoO6types of octahedra is axially distorted. The three other Sr positions occupy theAsite with higher coordination. There is an occupational deficit of O atoms of 22 (4)%. This defective framework material presents an interesting ionic mobility, enhanced above 773 K owing to a further reduction in the oxygen content.

ZnSe Quantum Dot Films Deposition from Modified Chemical Solution with Sodium Citrate

Zinc selenide (ZnSe) quantum dot thin films have been deposited onto microscope glass through chemical bath deposition both from original amonia free alkaline precursors and modified precursors with the adding of sodium citrate as complexing agents. The growth and optical properties of samples from original and modified precursors have been investigated. Its shown that the samples obtained with sodium citrate precursors are uniform and with stable index of refraction. And with the adding of sodium citrate, there is an increase in transmittance.

STRUCTURAL, ELECTRICAL AND MAGNETIC STUDIES OF Li–Zn–Ni FERRITES

Ni substituted Li – Zn ferrites with compositional formulas Li 0.4-0.5x Zn 0.2 Ni x Fe 2.4-0.5x O 4, where x = 0.02 ≤ x ≤ 0.1 in steps of 0.02, is synthesized by a chemical method using citrate precursors. The prepared ferrites are investigated for their structural, electrical and magnetic properties. Ni substitution significantly changes the characteristic properties of Li – Zn ferrites. There is an increase in grain growth as determined from SEM measurements. An increase in the room temperature DC resistivity is observed with the addition of Ni . The room temperature initial permeability shows an overall decrease with Ni concentration, which is explained with respect to saturation magnetization and supplemented by nuclear hyperfine field obtained from Mössbauer analysis. The variation of the complex permeability with frequency is measured over the frequency range of 100 Hz–1 MHz and dispersion is found. A possible mechanism contributing to the above process is discussed.