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Cation Sites (cation + site)
Selected AbstractsStructure and Dielectric Properties of Pb(Sc2/3W1/3)O3,Pb(Zr/Ti)O3 RelaxorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Pavol Juhás The structure and dielectric properties of (1,x)Pb(Sc2/3W1/3)O3,(x)Pb(Zr/Ti)O3 ceramics have been investigated over a full substitution range. All compositions with x < 0.5 adopt a cubic perovskite structure; however, for x, 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc2/3W1/3)O3 (PSW) can be described by a random-site model with one cation site occupied by Sc3+ and the other by a random distribution of (Sc1/33+W2/36+). The ordering is destabilized in solid solutions of PSW with PbZrO3 (PSW,PZ), but stabilized by PbTiO3 in the (1,x)PSW,(x)PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW,PZ the temperature of the permittivity maximum (T,,max) increases linearly with x; however, for PSW,PT T,,max decreases in the ordered region (up to x= 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW,(0.25)PT; when the order parameter was reduced from ,1.0 to ,0.65, T,,max increased by more than 60°C. [source] 3,6,9,16,19,22-Hexaazatricyclo[22.2.2.211,14]triconta-1(26),11(29),12,14(30),24,27-hexaene, C24H38N6, as a building block in supramolecular chemistry: structures in two and three dimensionsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2000Christopher Glidewell The adduct (1) formed between the hexaaza macrocycle 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]triconta-1(26),11(29),12,14(30),24,27-hexaene, C24H38N6, and 4,4,-sulfonyldiphenol, O2S(C6H4OH)2, is a salt [(C24H40N6)2+]·2[(HOC6H4SO2C6H4O),], and the adduct (2) formed by the same macrocyclic amine with 4,4,-biphenol is an aquated salt which also contains neutral biphenol molecules, [(C24H40N6)2+]·2[(HOC6H4C6H4O),]·(HOC6H4C6H4OH).2H2O. In both compounds the cations lie across centres of inversion: there are two crystallographically distinct cation sites in (1) and the conformations of the cations occupying them are quite different. In (2) the single type of cation site is occupied by a conformationally disordered cation: the major and minor components represent two further distinct conformers. In (1) the anions are linked by O,H,O hydrogen bonds into chains, and each cation is linked by a total of six N,H,O hydrogen bonds to anions in four different chains, so linking the chains into continuous sheets. In (2) the anions and the water molecules are linked into sheets, which are further linked into a continuous three-dimensional framework by both the cations and the neutral biphenol units. [source] Single crystal X-ray study of the modulated structure in Ga2XTe3 with the defect zinc-blende structurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009S. Kashida Abstract Ga2Te3 crystallizes into the zinc-blende structure, where one third of the cation sites is vacant. Single crystal X-ray diffraction studies on quenched and annealed Ga2Te3 and CuGaTe2 crystals are reported. The obtained diffraction maps show, other than the zinc-blende type main reflections, satellite reflections at q1,1/17[110]c in quenched Ga2Te3 crystals and q2,1/20[210]c in annealed Ga2Te3 crystals, where the subscript c means the cubic sub-lattice. The analysis of the satellite reflections shows that the modulation is two dimensional, and is ascribed to a coupled mode of the amplitude type modulation caused by Ga vacancies and the displacive modulation of surrounding Te atoms, which has the polarization vector along the <001>c direction. The nature of the atomic modulations is discussed and the origin of the modulation is ascribed to Jahn-Teller type distortions around Ga vacancies. The experiments done on CuGaTe2 crystals indicate that the cation disorder compound sphalerite type CuGaTe2 contain the same modulated structure as Ga2Te3 crystals, but the cation ordered compound chalcopyrite type CuGaTe2 does not show the modulation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of InCrN and (In,Ga,Cr)NPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008S. Kimura Abstract InCrN and a new quaternary alloy (In,Ga,Cr)N were synthesized by molecular beam epitaxy. Their structural properties were studied with X-ray diffraction and X-ray absorption fine structure (XAFS). It was found that low temperature growth enables the growth of InCrN and (In,Ga,Cr)N with higher Cr contents, while they were not crystallized at higher substrate temperature (450 °C). XAFS studies suggest that Cr atoms substitute on cation sites and no trace of locally formed secondary phases, such as Cr cluster, CrN (NaCl type) and Cr2N, in the grown InCrN and (In,Ga,Cr)N layers. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 3,6,9,16,19,22-Hexaazatricyclo[22.2.2.211,14]triconta-1(26),11(29),12,14(30),24,27-hexaene, C24H38N6, as a building block in supramolecular chemistry: structures in two and three dimensionsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2000Christopher Glidewell The adduct (1) formed between the hexaaza macrocycle 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]triconta-1(26),11(29),12,14(30),24,27-hexaene, C24H38N6, and 4,4,-sulfonyldiphenol, O2S(C6H4OH)2, is a salt [(C24H40N6)2+]·2[(HOC6H4SO2C6H4O),], and the adduct (2) formed by the same macrocyclic amine with 4,4,-biphenol is an aquated salt which also contains neutral biphenol molecules, [(C24H40N6)2+]·2[(HOC6H4C6H4O),]·(HOC6H4C6H4OH).2H2O. In both compounds the cations lie across centres of inversion: there are two crystallographically distinct cation sites in (1) and the conformations of the cations occupying them are quite different. In (2) the single type of cation site is occupied by a conformationally disordered cation: the major and minor components represent two further distinct conformers. In (1) the anions are linked by O,H,O hydrogen bonds into chains, and each cation is linked by a total of six N,H,O hydrogen bonds to anions in four different chains, so linking the chains into continuous sheets. In (2) the anions and the water molecules are linked into sheets, which are further linked into a continuous three-dimensional framework by both the cations and the neutral biphenol units. [source] Use of complementary cation and anion heavy-atom salt derivatives to solve the structure of cytochrome P450 46A1ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2008Mark Andrew White Human cytochrome P450 46A1 (CYP46A1) is one of the key enzymes in cholesterol homeostasis in the brain. The crystallization and heavy-atom structure solution of an active truncated CYP46A1 in complex with the high-affinity substrate analogue cholesterol-3-sulfate (CH-3S) is reported. The 2.6,Å structure of CYP46A1,CH-3S was solved using both anion and cation heavy-atom salts. In addition to the native anomalous signal from the haem iron, an NaI anion halide salt derivative and a complementary CsCl alkali-metal cation salt derivative were used. The general implications of the use of halide and alkali-metal quick soaks are discussed. The importance of using isoionic strength buffers, the titration of heavy-atom salts into different ionic species and the role of concentration are considered. It was observed that cation/anion-binding sites will occasionally overlap, which could negatively impact upon mixed RbBr soaks used for multiple anomalous scatterer MAD (MMAD). The use of complementary cation and anion heavy-atom salt derivatives is a convenient and powerful tool for MIR(AS) structure solution. [source] | ||||||||||