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C Parameter (c + parameter)
Selected AbstractsGrowth and characterization of FexMn1-xIn2Se4 (0 , x , 1) single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005G. Attolini Abstract Single crystals of Mn1-xFexIn2Se4 with 0 , x , 1.0 were grown by chemical vapor transport technique using I2 as transporting agent. The resulting crystals appeared as brilliant black plates. X-ray powder diffraction data could be indexed following the hexagonal structure with space group Rm for the low Fe concentration samples, while the high concentration sample is associated to the space group P63mc. Both polytypes have similar parameters, however the c parameter reduces as the Fe concentration increases, therefore the number of anion slabs decreases. The characterization of the crystals was based on morphological observations and optical absorption as a function of temperature. The obtained energy gap for the samples at different Fe concentrations suggested that they behave as direct energy gap semiconductors. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Titanium Diboride,Tungsten Diboride Solid Solutions Formed by Induction-Field-Activated Combustion SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Masachika Shibuya Solid solutions of titanium diboride,tungsten diboride (TiB2,WB2) were synthesized by induction-field-activated combustion synthesis (IFACS) using elemental reactants. In sharp contrast to conventional methods, solid solutions could be formed by the IFACS method within a very short time, ,2 min. Solutions with compositions ranging from 40,60 mol% WB2 were synthesized with a stoichiometric ratio (Ti + W)/B =½; however, samples with excess boron were also made to counter the loss of boron by evaporation. The dependence of the lattice constants of the resulting solid solutions on composition was determined. The "a" parameter decreased only slightly with an increase in the WB2 content, whereas the "c" parameter exhibited a significant decrease over the range 40,60 mol% WB2. Solid-solution powders formed by the IFACS method were subsequently sintered in a spark plasma sintering (SPS) apparatus. After 10 min at 1800°C, the samples densified to relative density 86%. XRD analysis showed the presence of only the solid-solution phase. [source] The OD interpretation of the crystal structure of kettnerite CaBiOFCO3ACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2009í Hybler The mineral kettnerite, CaBi(OFCO3), is a rare example of an order,disorder (OD) structure with a quadratic net. The lattice parameters of the simplest possible 1O polytype are a = 5.3641,(1), b = 5.3641,(1), c = 13.5771,(2),Å, and the space group is Pbaa. There are three kinds of OD layers, identical to structure-building layers. Two of them are non-polar: the Bi,O and Ca,F at z = 0 and z = 1/2, respectively, with the layer-group symmetry C2/m2/m(4/a,b)21/m21/m. The third kind of OD layer of CO3 groups (located between the Bi,O and Ca,F layers) is polar, with alternating sense of polarity. The layer group is Pba(4)mm. Triangular CO3 groups are parallel to (110) or () planes with one O atom oriented towards the Bi,O layer and the remaining two O atoms oriented towards the Ca,F layer. The orientations of CO3 groups alternate along the [110] and [] directions. As a result, each group parallel to (110) is surrounded by four nearest neighbors parallel to () and vice versa. These positions can be interchanged by an (a + b)/2 shift or by ,/2 rotation; thus stacking of the layer onto adjacent ones is ambiguous. Instead of OD layers, the polytypes are generated by stacking of OD packets, comprising the whole CO3 layers and adjacent halves of the Bi,O and Ca,F layers. They are polar, with alternating sense of polarity; the layer group is Pba(4)mm. Stacking sequences are expressed by ball-and-stick models, with the aid of symbolic figures, and by sequences of orientational characters. There are two maximum-degree-of-order (MDO) polytypes, 1O (really found and described, see lattice parameters and space group above) and 2O, with doubled c parameter and space group Ibca (not yet found). The derivation of the MDO generating operations of both polytypes is presented in this paper. The stacking rule also allows another, non-MDO, polytype with doubled c, i.e. the 2Q polytype, space group P42bc (tetragonal, not yet found). Various kinds of domains can exist: (i) out-of-step domains shifted by (a + b)/2, (ii) twin domains rotated by ,/2 around local tetrads of odd or even packets, and (iii) upside-down domains in the polar 2Q polytype. Stacking sequences of 16 possible domains of the polytypes mentioned above are listed. Also 60 domains of four distinct six-packet polytypes are theoretically possible. [source] Intersubsystem chemical bonds in the misfit layer compounds (LaS)1.13TaS2 and (LaS)1.14NbS2ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2002Andreas Jobst The modulated structures of incommensurate composite crystals (La0.912S)1.13TaS2 at room temperature and of (La0.949S)1.14NbS2 at T = 115,K are refined against high-resolution X-ray data. The compounds are isostructural with superspace group F,m2m(,,0,0)00s. For (LaS)1.13TaS2, lattice parameters of the first subsystem TaS2 were obtained as a = 3.2922,(1), b = 5.7776,(2) and c = 23.013,(2),Å. For the second subsystem LaS, the same b and c parameters were found, but a = 5.8090,(8),Å. Refinements led to a final structure model with R = 0.036 for 4767 observed unique reflections (R = 0.023 for 2147 main reflections, R = 0.099 for 1554 first-order satellites and R = 0.112 for 1042 second-order satellites). The final model includes modulation parameters up to the second-order harmonics for the displacements of the atoms, for the occupational parameters and for the temperature parameters. A clear correlation is found between the relative positions of the subsystems, the displacement modulation, the occupational modulation and the modulation of the temperature parameters. The analysis shows that the variations in environments are resolved by correlated variations in the temperature factors. For (LaS)1.14NbS2, lattice parameters at T = 115,K of the NbS2 subsystem were obtained as a = 3.3065,(4), b = 5.7960,(5) and c = 22.956,(3),Å. For the LaS subsystem, the same values for b and c were obtained, but a = 5.7983,(7),Å. Refinements led to a final structure model with R = 0.048 for 5909 observed unique reflections (R = 0.034 for 2528 main reflections, R = 0.092 for 2171 first-order satellites and R = 0.113 for 1103 second-order satellites). The final structure model is similar to that of (LaS)1.13TaS2. In particular, it is found that the values of the modulation parameters are almost equal and it is concluded that the modulations are independent of the temperature and the replacement of Ta with Nb, and thus represent a general mechanism of resolving the strain between the mutually incommensurate layers. [source] Structural Evidence for Zn Intersititials in Ferromagnetic Zn1,xCoxO Films,ADVANCED MATERIALS, Issue 19 2007L. MacManus-Driscoll Post-annealing studies in different atmospheres combined with high resolution x-ray studies on epitaxial ZnO and Zn1,xCoxO films revealed that the c -axis lattice parameter decreases when interstitial zinc is removed from ZnO. The ,c' parameter change reverses sign when samples are re-annealed in a Zn-rich atmosphere. Stronger ferromagnetism occurs in Zn1,xCoxO film for higher ,c' parameters and hence higher Zn interstitial concentrations. [source] | |||||||||||||