scholarly journals Thermal History Dependent Al Distribution in Aluminum Substituted Strontium Hexaferrite

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 858
Author(s):  
Manuel Häßner ◽  
Denis A. Vinnik ◽  
Rainer Niewa
Keyword(s):  
Single Crystals ◽  
Annealing Time ◽  
Magnetic Measurements ◽  
Strontium Hexaferrite ◽  
X Ray ◽  
Al Content ◽  
Substitution Level ◽  
Corundum Crucible ◽  
Al Distribution ◽  
Annealing Experiments

Single crystals of aluminum substituted strontium hexaferrite SrFe12–xAlxO19 were grown from sodium oxide based flux. The substitution level aimed for was x = 1.2. Annealing experiments performed on single crystals show that the Al distribution on the five iron sites of the hexaferrite structure depends on the annealing time at 900 °C. Single crystal X-ray diffractometry shows that annealing a crystal after the initial synthesis has an impact on the Al content on the octahedrally and tetrahedrally coordinated sites. Furthermore, it was found that heating in a corundum crucible increases the overall Al content. Magnetic measurements show that annealing in a platinum or corundum crucible decreases coercivity and remanence while the saturation magnetization is hardly influenced.

Superconductivity and Magnetism in the La2 CuO4-Based Compounds

MRS Bulletin ◽  
1989 ◽  
Vol 14 (1) ◽  
pp. 33-36 ◽  
Author(s):  
Z. Fisk ◽  
S-W. Cheong ◽  
D.C. Johnston
Keyword(s):  
Single Crystals ◽  
Magnetic Measurements ◽  
Oxygen Stoichiometry ◽  
Layered Perovskite ◽  
Orthorhombic Distortion ◽  
X Ray ◽  
Bulk Superconductivity ◽  
High Oxygen Pressure ◽  
Powder Samples ◽  
Cation Ratio

La2CuO4, crystallizes in an orthorhombic distortion of the tetragonal K2NiF4 structure, a so-called layered perovskite. The important question here concerns the stoichiometry of La2CuO4 prepared by various techniques. Regarding the La and Cu sites, recent neutron diffraction studies of powders have shown that the La:Cu ratio can vary from 2:1 by ≳1% in various preparations., Single crystals have been grown variously from CuO, PbO and Li2O-B2O3 fluxes. The last two fluxes incorporate some Pb and Li, respectively, into the crystals, but the cation ratio is found to be 2:1 within the accuracy of x-ray refinement.It is also known that the oxygen stoichiometry corresponds to La2CuO4 within ≃ 1%. Extensive and precise magnetic susceptibility (χ) and other studies of powder samples showed, however, that the physical properties are extremely sensitive to < 1% changes in the oxygen content. A clear indication from electric and magnetic measurements is that the oxygen stoichiometry is always that, or richer than that, corresponding to a Mott insulator with an exactly half-filled band. Consistent with this, the stoichiometry is more properly written La2-z CuO4-y with small, positive y and z.Several groups found that bulk superconductivity above 30 K can be produced in La2CuO4 by annealing powders or single crystals at high oxygen pressure. The weight gain in this process corresponds to producing La2CuO4.13, and these authors believe the excess oxygens go in as O-2, based on iodometric titration measurements giving the amount of [Cu-O]⊥ in the sample. Jorgensen et al. found that there is a phase separation below 320 K of La2CuO4 and the O2-loaded phase in oxygen-rich samples; the latter structure is also orthorhombic, but the position of the excess oxygens could not be determined unambiguously.

Growth of Lead and Aluminum Substituted Barium Hexaferrite Single Crystals from Lead Oxide Flux

2016 ◽  
Vol 843 ◽  
pp. 3-9 ◽  
Author(s):  
D.A. Vinnik ◽  
S.A. Gudkova ◽  
R. Niewa
Keyword(s):  
Single Crystals ◽  
Lead Oxide ◽  
Barium Hexaferrite ◽  
Cell Parameters ◽  
Al Content ◽  
Substitution Level ◽  
Bulk Single Crystals ◽  
First Time ◽  
Oxide Flux ◽  
Substituted Barium Hexaferrite

Lead and aluminum substituted barium hexaferrite (Ba,Pb)Fe12–хAlхO19 single crystals were grown from lead oxide flux at 1260 °C as hexagonal plates with sizes of about 2 mm. A maximum substitution level of x = 4.82 was achieved for the first time for bulk single crystals. The variation of the unit cell parameters with Al content is in good agreement with literature data on exclusively Al substituted barium hexaferrite, while the substitution of Ba by Pb has hardly any influence. Similarly, Pb has only a negligible influence on the magnetic properties, while Al substitution significantly reduces the saturation magnetization in a very similar manner as known from Pb-free barium hexaferrite.

Crystal structure and physical properties of GaSe single crystals annealed in sulfur atmosphere

2005 ◽  
Vol 891 ◽  
Author(s):  
Olga V. Voevodina ◽  
Aleksandr N. Morozov ◽  
Sergey Yu. Sarkisov ◽  
Yuri M. Andreev ◽  
Nils C. Fernelius ◽  
...  
Keyword(s):  
Single Crystals ◽  
Gas Phase ◽  
Interlayer Space ◽  
Structure And Properties ◽  
X Ray ◽  
Crystal Properties ◽  
Sulfur Atmosphere ◽  
Optical Applications ◽  
Nonlinear Optical Applications ◽  
Annealing Experiments

ABSTRACTIn spite of the progress in GaSe growing technology (high-quality crystals grown by the latest technology are characterized by low values of optical losses with the absorption coefficient values lying below 0.1 cm−1) the work continues on improving crystal properties for nonlinear optical applications. This paper presents the results of investigations on the influence of annealing in a sulfur atmosphere and in a vacuum on the properties GaSe single crystals, grown by the Bridgman method from the melt. The objective of this work was to study the possibility of intercalating GaSe with sulfur from the gas phase, and to compare the influence of doping with sulfur from melt and vapor phase on the structure and properties of GaSe crystals. Three series of annealing experiments have been conducted at temperatures 773, 923, 1073 K and the samples obtained have been studied by Hall effect, photoconductivity, optical absorption, microhardness measurements and X ray diffractometry. The results obtained are explained by assuming the intercalating of sulfur to the interlayer space and substitution of Se with S.

Structural and Magnetic Properties of Untwinned Yba2Cu3O6+x Single Crystals

1989 ◽  
Vol 169 ◽  
Author(s):  
Debra L. Kaiser ◽  
Frank W. Gayle ◽  
Lydon J. Swartzendruber ◽  
Winnie Wong-Ng ◽  
Steven F. Watkins ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Single Crystals ◽  
Flux Pinning ◽  
Magnetic Measurements ◽  
Mirror Plane ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural And Magnetic Properties ◽  
Low Levels ◽  
Superconducting Onset Temperature

AbstractWe have conducted structural and magnetic investigations on thermomechanically-detwinned YBa2Cu3O6+x single crystals. Single crystal x-ray diffraction studies on a fully untwinned crystal with a superconducting onset temperature of 54 K have revealed that oxygen atoms in the basal plane are offset from the crystallographic mirror plane in the a direction, leading to “zig-zag” Cu-O chains. Magnetic measurements on untwinned and twinned crystals at 77 K indicate low levels of flux pinning in both crystals, with a slightly larger amount of pinning in the twinned crystal.

Zone-axis ALCHEMI for the rapid assessment of site occupancies in garnets

1986 ◽  
Vol 44 ◽  
pp. 706-707
Author(s):  
M.T. Otten ◽  
P.R. Buseck
Keyword(s):  
Single Crystals ◽  
Rapid Assessment ◽  
Site Occupancy ◽  
Zone Axis ◽  
Synthetic Compounds ◽  
X Ray ◽  
Large Group ◽  
Crystallographic Planes

ALCHEMI (Atom Location by CHannelling-Enhanced Microanalysis) is a TEM technique for determining site occupancies in single crystals. The method uses the channelling of incident electrons along specific crystallographic planes. This channelling results in enhanced x-ray emission from the atoms on those planes, thereby providing the required site-occupancy information. ALCHEMI has been applied with success to spinel, olivine and feldspar. For the garnets, which form a large group of important minerals and synthetic compounds, the channelling effect is weaker, and significant results are more difficult to obtain. It was found, however, that the channelling effect is pronounced for low-index zone-axis orientations, yielding a method for assessing site occupancies that is rapid and easy to perform.

Effect of trytophan as dopant on potassium acid phthalate single crystals

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Single Crystals ◽  
Room Temperature ◽  
Visible Region ◽  
X Ray Diffraction ◽  
X Ray ◽  
Slow Evaporation Technique ◽  
Absorption Studies ◽  
Evaporation Technique ◽  
Potassium Acid Phthalate ◽  
Acid Phthalate

Optically transparent single crystals of potassium acid phthalate (KAP, 0.5 g) 0.05 g and 0.1 g (1 and 2 mol %) trytophan were grown in aqueous solution by slow evaporation technique at room temperature. Single crystal X- ray diffraction analysis confirmed the changes in the lattice parameters of the doped crystals. The presence of functional groups in the crystal lattice has been determined qualitatively by FTIR analysis. Optical absorption studies revealed that the doped crystals possess very low absorption in the entire visible region. The dielectric constant has been studied as a function of frequency for the doped crystals. The thermal stability was evaluated by TG-DSC analysis.

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