Growth of High-Purity and Doped Alkaline Earth Oxides: I. MgO and CaO

Research Summary Spintronic Materials and DevicesWe have investigated the magnetic properties of the Ni-MgO system with an Ni concentration of 0.5 at.%. In asgrown crystals, Ni ions occupy substitutional Mg sites. Under these conditions the Ni-MgO system behaves as a perfect paramagnet. By using a controlled annealing treatment in a reducing atmosphere, we were able to induce clustering and form pure Ni precipitates in the nanometer size range. The size distribution of precipitates or nanodots is varied by changing annealing time and temperature. Magnetic properties of specimens ranging from perfect paramagnetic to ferromagnetic characteristics have been studied systematically to establish structure-property correlations. The spontaneous magnetization data for the samples, where Ni was precipitated randomly in MgO host, fi ts well to Bloch's T 3/2 -law and has been explained within the framework of spin wave theory predictions.

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“…[7][8][9] In asgrown crystals, Ni ++ ions occupy substitutional Mg ++ sites. These crystals exhibit green color emission at room temperature.…”

Section: Methodsmentioning

confidence: 99%

The synthesis and magnetic properties of a nanostructured Ni-MgO system

Narayan

Shibata

Ramachandran

et al. 2009

JOM

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“…The situation is also reflected by the extremely low stacking-fault energy. 6 The stacking order of S i c crystals thus seems to be affected by local growth conditions,'" as demonstrated by the distribution of disordered crystals in the present case. One-dimensionally-disordered crystals, however, should not be considered simply as heavily faulted 3C crystals.…”

mentioning

confidence: 50%

“….Sri , 7 [6] 723-26 (1972 '" D. Pandey and P. Krishna; in Ref. 6. " S. Shinozakj and K. R. Kinsman, "Aspects of 'One Dimensional Disorder' in Silicon Carbide, Amr Meto//., 26, 769-76 (1978) Carbon Content of High-Purity Alkaline Earth Oxide Single Crystals Grown by Arc Fusion…”

mentioning

confidence: 99%

Carbon Content of High‐Purity Alkaline Earth Oxide Single Crystals Grown by Arc Fusion

Freund

Debras

Demortier

1978

Journal of the American Ceramic Society

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On the fine scale revealed by TEM, the material is characterized by predominant dendritic 3C crystals. All these dendritic crystals have equivalent orientations and are not polycrystals like those found in dendritic growth of metals. The branching-off characteristic of 3C dendritic growth is thus due to symmetry of its having three equivalent close-packed directions. Since both trunks and branches have exactly the same orientation and since the direction of the spines is parallel to the < 1 1 1 > directions, S i c crystals seem to grow in one of the < 1 1 1 > directions under the present conditions. Some X crystals were also found to grow in a columnar fashion in one of the < I 11> directions, much as in S i c whiskers. These columnar crystals exhibit twin bands perpendicular to the growth direction.Both the 2H and the one-dimensionally-disordered crystals are uniaxial and grow in acolumnarfashion in thec direction. SinceSiC does not usually form regular crystalline boundaries between crystals of different orientation, as observed in common metals, presumably because of the high energy involved in dislocation formation, these crystals do not form dendritic structures with branching-off as do the 3C crystals. However, several onedimensionally-disordered crystals were found to grow together with a columnar habit, making small angles with one another. Precise details of the structure of such small-angle grain boundaries are not known .The one-dimensionally-disordered crystals are characterized by the fact that the stacking order of the crystal is almost completely random, whereas the structure is perfect in the other two dimensions. The existence of the one-dimensionally-disordered structure reflects the general characteristic of polytypism of S i c , i.e. that the energy of the structure does not depend on its stacking order and that any polytype is equally pr~bable.~.'" The situation is also reflected by the extremely low stacking-fault energy.6 The stacking order of S i c crystals thus seems to be affected by local growth conditions,'" as demonstrated by the distribution of disordered crystals in the present case. One-dimensionally-disordered crystals, however, should not be considered simply as heavily faulted 3C crystals. ,A study of such one-dimensionally-disordered crystals by highresolution electron microscopyz1 revealed that the structure con-sisted of random layers of thin a-and P-phase lamellas of various thicknesses.2t Acknowledgments: The writers are indebted for valuable discussions to J. E.

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“…MgO crystals undoped and doped with H, Li, or Ni were grown by an arcfiision technique [2]. Large hydrogen content can be obtained by presoaking MgO powder with water.…”

Section: Methodsmentioning

confidence: 99%