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Mg Atoms (mg + atom)
Selected AbstractsCe20Mg19Zn81: a new structure type with a giant cubic cellACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Volodymyr Pavlyuk Icosacerium nonadecamagnesium henoctacontazinc, Ce20Mg19Zn81, synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F3m, a = 21.1979,(8),Å] and represents a new structure type among the technologically important family of ternary rare earth,transition metal,magnesium intermetallics. The majority of atoms (two Ce and five Zn) display .3m site symmetry, two Ce and one Mg atom occupy three 2.mm positions, one Mg and one Zn have 3m site symmetry, one Mg and three Zn atoms sit in ..m positions, and one Zn atom is in a general position. The Ce20Mg19Zn81 structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz. A (Zn+Zn4+Zn4+Zn12+Ce6), B (Mg+Zn12+Ce4+Zn24+Ce4), C (Zn4+Zn12+Mg6) and D (Zn4+Zn4+Mg12+Ce6), with the outer construction unit being an octahedron or tetrahedron. All interatomic distances in the structure indicate metallic-type bonding. [source] Tb2Ni2Mg3: a new structure type derived from the Ru3Al2B2 typeACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2007Pavlo Solokha Single crystals of diterbium dinickel trimagnesium, Tb2Ni2Mg3, were synthesized from the elements by induction melting. The novel compound crystallizes in the space group Cmmm with one Mg atom of site symmetry mmm and the Tb, Ni and other Mg atom in m2m positions. This ternary compound represents a new structure type that is derived from Ru3Al2B2 by way of Wyckoff site distribution. The two-layer structure of Tb2Ni2Mg3 is a new representative of a homologous linear structure series of general formula R,k+nX2nR,,2m+k based on structural fragments of the ,-Fe, CsCl and AlB2 structure types. The Tb atoms in the structure are enclosed in 17-vertex polyhedra, while rhombododecahedra and distorted rhombododecahedra surround the Mg atoms, and equatorially tricapped trigonal prisms form around the Ni atoms. All interatomic distances indicate metallic type bonding. [source] Bis(ammonium) tris(hexaaquamagnesium) tetrakis(hydrogen phosphite)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2006Khaoulani Idrissi Abdallah The structure of the title compound, (NH4)2[Mg(H2O)6]3(HPO3)4, consists of [Mg(H2O)6]2+ and (NH4)+ cations and (HPO3)2, anions held together by an intricate network of hydrogen bonds involving all H atoms except for one linked directly to a P atom. The Mg2+ cations are octahedrally coordinated by six water molecules. One of the Mg atoms is located on a site with 2/m symmetry, whereas the other Mg atom and the P and N atoms occupy sites with m symmetry. [source] Sodium magnesium bis(vanadate) pyrovanadate: Na6Mg2(VO4)2(V2O7)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2004Alexander Mitiaev The crystal structure of the new complex vanadium oxide Na6Mg2(VO4)2(V2O7) was solved from X-ray single-crystal data. The structure contains VO4 tetrahedra and MgO6 octahedra, linked by corners and forming a complex three-dimensional framework. A half of the VO4 tetrahedra are connected only to MgO6 octahedra, whereas the others are corner-sharing, forming V2O7 pyrovanadate groups with statistically random orientations. One unique Mg atom is located at an inversion centre, while the other Mg atom, one unique V atom and five unique O atoms lie on mirror planes. [source] (Z)-Bis{,-[1-(2-naphthylmethyloxy)propan-2-iminato- O,N:N]}bis[bromobis(tetrahydrofuran- O)magnesium] ditoluene solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000André B. Charette The title compound, [Mg2Br2(C14H14NO)2(C4H8O)4]·2C7H8, has been crystallized as a C2 -symmetric dimer and the Mg atom has a distorted octahedral geometry. The metal is chelated by the N atom of the ketiminate and the O atom of the ether moiety, giving a rigid structure. [source] Local 3D real space atomic structure of the simple icosahedral Ho11Mg15Zn74 quasicrystal from PDF dataCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2003S. Brühne Abstract We present a new complementary strategy to quasicrystalline structure determination: The local atomic structure of simple icosahedral (si) Ho11Mg15Zn74 [a(6D) = 5.144(3)Å in a sphere of up to r = 17Å was refined using the atomic pair distribution function (PDF) from in-house X-ray powder diffraction data (MoK,1, Qmax = 13.5Å,1; R = 20.4%). The basic building block is a 105-atom Bergman-Cluster {Ho8Mg12Zn85}. Its center is occupied by a Zn atom , in contrast to a void in face centred icosahedral (fci) Ho9Mg26Zn65. The center is then surrounded by another 12 Zn atoms, forming an icosahedron (1st shell). The 2nd shell is made up of 8 Ho atoms arranged on the vertices of a cube which in turn is completed to a pentagon dodecahedron by 12 Mg atoms, the dodecahedron then being capped by 12 Zn atoms. The 3rd shell is a distorted soccer ball of 60 Zn atoms, reflecting the higher Zn content of the si phase compared to the fci phase. In our model, 7% of all atoms are situated in between the clusters. The model corresponds to a hypothetical 1/1-approximant of the icosahedral (i) phase. The local coordinations of the single atoms are of a much distorted Frank-Kasper type and call to mind those present in 0/1-Mg2Zn11. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exciton states and tunneling in semimagnetic asymmetric double quantum wellsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010S. V. Zaitsev Abstract Exciton level structure and interwell relaxation are studied in Cd(Mn,Mg)Te-based asymmetric double quantum wells (ADQWs) by a steady-state optical spectroscopy in magnetic fields up to B,=,10,T. The as grown heterostructures with CdTe QWs and nonmagnetic interwell CdMgTe barrier were subjected to a rapid temperature annealing to introduce Mn and Mg atoms from opposite barriers inside the QWs which results in a formation of the ADQW with completely different magnetic field behavior of the intrawell excitons. The giant Zeeman effect in the QW with magnetic Mn ions gives rise to a crossing of the ground exciton levels in two QWs at BC,,,3,6,T which is accompanied by a reverse of the interwell tunneling direction. In a single-particle picture the exciton tunneling is forbidden at B,<,1,T as supported by calculations. Experimentally, nevertheless, a very efficient interwell relaxation of excitons is found at resonant excitation in the whole magnetic field range, regardless of the tunneling direction, emphasizing importance of excitonic correlations in the interwell tunneling. At nonresonant excitation an unexpectedly slow relaxation of the ,, -polarized excitons from the nonmagnetic QW to the ,+ -polarized ground state in the semimagnetic QW is observed at B,>,BC, giving rise to a nonequilibrium distribution of excitons in ADQW. A strong dependence of the total circular polarization degree on the hh,lh splitting ,hh,lh in the nonmagnetic QW is found and attributed to the spin dependent interwell tunneling controlled by an exciton spin relaxation. Different charge-transfer mechanisms are analyzed in details and an elastic scattering due to a strong disorder is suggested as the main tunneling mechanism with the underlying influence of the valence band-mixing. [source] Determination of the Mg occupation site in MOCVD- and MBE-grown Mg-doped InN using X-ray absorption fine-structure measurementsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Takao Miyajima Abstract We analyzed the atomic structure around Mg atoms in MOCVD- and MBE-grown Mg-doped InN using Mg K-edge X-ray absorption fine-structure (XAFS) measurements. Our experimental data closely fit to the simulated data in which Mg atoms occupy the substitutional sites of In atoms. From this result, we conclude that Mg atoms essentially occupy not N atoms sites but In atoms sites, meaning that Mg atoms can act as acceptors in InN. We believe that observations of p-type conductivity are prevented by problems such as carrier compensation and electron accumulation at the surface. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Composition influence on positron annihilation parameters in ZnO-based nanocrystal semiconductor powdersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007L. C. Damonte Abstract Zn1,xMgxO powders at various compositions were obtained by mechanical milling from the binary oxides. The progressive incorporation of Mg atoms into the ZnO lattice was monitored by X-ray diffraction (XRD). The evolution of annihilation parameters with milling time and composition were analyzed and related to the possible types of mechanical and substitutional induced defect present. It was concluded that the average lifetime constitute a useful parameter to sense the complete cation substitution in the wurtzite structure. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Features of the electron density in magnesium diboride: reconstruction from X-ray diffraction data and comparison with TB-LMTO and FPLO calculationsACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2003S. Lee Features of the electron density in MgB2 reconstructed from room-temperature single-crystal X-ray diffraction intensities using a multipole model are considered. Topological analysis of the total electron density has been applied to characterize the atomic interactions in magnesium diboride. The shared-type B,B interaction in the B-atom layer reveals that both , and , components of the bonding are strong. A closed-shell-type weak B,B , interaction along the c axis of the unit cell has also been found. The Mg,B closed-shell interaction exhibits a bond path that is significantly curved towards the vertical Mg-atom chain ([110] direction). The latter two facts reflect two sorts of bonding interactions along the [001] direction. Integration of the electron density over the zero-flux atomic basins reveals a charge transfer of ,1.4,(1) electrons from the Mg atoms to the B-atom network. The calculated electric-field gradients at nuclear positions are in good agreement with experimental NMR values. The anharmonic displacement of the B atoms is also discussed. Calculations of the electron density by tight-binding linear muffin-tin orbital (TB-LMTO) and full-potential non-orthogonal local orbital (FPLO) methods confirm the results of the reconstruction from X-ray diffraction; for example, a charge transfer of 1.5 and 1.6 electrons, respectively, was found. [source] Tb2Ni2Mg3: a new structure type derived from the Ru3Al2B2 typeACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2007Pavlo Solokha Single crystals of diterbium dinickel trimagnesium, Tb2Ni2Mg3, were synthesized from the elements by induction melting. The novel compound crystallizes in the space group Cmmm with one Mg atom of site symmetry mmm and the Tb, Ni and other Mg atom in m2m positions. This ternary compound represents a new structure type that is derived from Ru3Al2B2 by way of Wyckoff site distribution. The two-layer structure of Tb2Ni2Mg3 is a new representative of a homologous linear structure series of general formula R,k+nX2nR,,2m+k based on structural fragments of the ,-Fe, CsCl and AlB2 structure types. The Tb atoms in the structure are enclosed in 17-vertex polyhedra, while rhombododecahedra and distorted rhombododecahedra surround the Mg atoms, and equatorially tricapped trigonal prisms form around the Ni atoms. All interatomic distances indicate metallic type bonding. [source] Bis(ammonium) tris(hexaaquamagnesium) tetrakis(hydrogen phosphite)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2006Khaoulani Idrissi Abdallah The structure of the title compound, (NH4)2[Mg(H2O)6]3(HPO3)4, consists of [Mg(H2O)6]2+ and (NH4)+ cations and (HPO3)2, anions held together by an intricate network of hydrogen bonds involving all H atoms except for one linked directly to a P atom. The Mg2+ cations are octahedrally coordinated by six water molecules. One of the Mg atoms is located on a site with 2/m symmetry, whereas the other Mg atom and the P and N atoms occupy sites with m symmetry. [source] | |||||||||||||