Search results for "Crystal system"
showing 10 items of 13557 documents
X-ray investigation and discussion of the magnetostriction of Gd3T(T= Ni, Rh, Irx) single crystals
2000
The variations of the lattice parameters of Gd3T(T= Ni, Rh, Irx) single crystals with temperature were measured in the range 10–300 K. The compounds with Ni and Rh crystallize in the orthorhombic space groupPnma, but the compound with Ir crystallizes as Gd5Ir2in the monoclinic space groupA2/a. The three compounds exhibit an anomalous anisotropic spontaneous magnetostriction below the magnetic ordering temperature.
Quasinodal lines in rhombohedral magnetic materials
2021
A well-established result in condensed matter physics states that materials crystallizing in symmetry groups containing glide reflection symmetries possess nodal lines on the energy bands. These nodal lines are topologically protected and appear on the fixed planes of the reflection in reciprocal space. In the presence of inversion symmetry, the energy bands are degenerate and the nodal lines on the fixed plane may hybridize or may cross. In the former case, the crossing is avoided, thus producing lines on reciprocal space where the energy gap is small, and in the latter, the nodal lines will endure, thus producing Dirac or double nodal lines. In addition, if the material crystallizes in a …
Spin crossover in iron(II) tris(2-(2′-pyridyl)benzimidazole) complex monitored by variable temperature methods: synchrotron powder diffraction, DSC, …
2003
Abstract The thermal expansion of the spin crossover system [Fe(pybzim) 3 ](ClO 4 ) 2 · H 2 O (pybzim=2-(2 ′ -pyridyl)benzimidazole) has been determined from powder X-ray data between 50 and 250 K; the wavelength of the synchrotron source was 1.21888(1) A. The unit cell parameters of the triclinic crystal system were a =12.091 A, b =12.225 A, c =14.083 A, α =77.70°, β =80.35°, γ =74.35°, and V =1944.9 A 3 at 250 K. In addition to the linear thermal expansion of the unit cell volume, an extra expansion due to the low-spin (LS) to high-spin (HS) transition is observed. The V ( T ) function shows a sudden increase comparable with the step in the effective magnetic moment at the transition reg…
Structural effects of Co and Cr substitution in LaMnO3 + δ
2000
Series of perovskite oxides with the composition LaMn1 − xMxO3 + δ (M = Cr, Co; 0 ≤ x ≤ 1) have been synthesized by thermal treatment of precursors obtained by freeze-drying of acetic acid solutions. The oxides have been characterized by X-ray diffraction, and the Mn4+ content and, thus, the oxygen excess, δ, has been determined by redox back-titration. LaMnO3.14 and LaCrO3 phases have the rhombohedral-LaAlO3 and the orthorhombic-GdFeO3 structures, respectively. The LaMn1 − xCrxO3 + δ phases have the rhombohedral structure for x ≤ 0.3, and the orthorhombic structure for x ≥ 0.5. LaCoO3 has, as LaMnO3.14, the rhombohedral structure. However, the LaMn1 − xCoxO3 + δ phases have orthorhombic st…
Molecular association in low-temperature and high-pressure polymorphs of 1,1,1,2-tetrachloroethane
2010
Interactions and aggregation of 1,1,1,2-tetrachloroethane molecules, Cl3CCH2Cl, have been investigated at low temperature and high pressure. Isobaric and isochoric crystallizations led to two polymorphs, characterized by single-crystal X-ray diffraction. The low-temperature polymorph α is monoclinic, space group C2/c, with molecules orientationally disordered in two sites at the temperature independent 70:30 rate. In isothermal conditions (295 K) 1,1,1,2-tetrachloroethane freezes at 0.73 GPa. The high-pressure polymorph β is monoclinic, space group P21/c, with the molecules fully ordered. The molecular aggregation at varied thermodynamic conditions results from the interplay of halogen inte…
Crystal Structure of the Microwave Dielectric Resonator Ba2Ti9O20
1983
A single-crystal X-ray study of dibarium nonatitanate, Ba2Ti9O20, yielded the triclinic space group P 1 with a=0.7471(1), b= 1.4081(2), c= 1.4344(2) nm, α=89.94(2)°, β= 79.43(2)°, γ= 84.45(2)°, V = 1.476 nm3 Z = 4, and Dx= 4.61 Mg/m3. A refinement of atomic coordinates and isotropic thermal parameters led to a residual of 0.03. The structure consists of hexagonally closest-packed layers of Ba and O atoms in the sequence (hch)3. All Ti atoms reside in octahedral interstices of this closest packing. The various Ti coordination octahedra share only edges and corners with each other. One-half of the Ba atoms is twelve-coordinated by oxygen atoms, the other half is eleven-coordinated.
The solid-state architecture of a metallosupramolecular polyelectrolyte
2006
Self-assembly of Fe(II) and the ditopic ligand 1,4-bis(2,2′:6′,2″-terpyridine-4′-yl)benzene results in equilibrium structures in solutions, so-called metallosupramolecular coordination polyelectrolytes (MEPEs). It is exceedingly difficult to characterize such macromolecular assemblies, because of the dynamic nature. Therefore, hardly any structural information is available for this type of material. Here, we show that from dilute solutions, where small aggregates predominate, it is possible to grow nanoscopic crystals at an interface. A near atomic resolution structure of MEPE is obtained by investigating the nanoscopic crystals with electron diffraction in combination with molecular model…
Polymorphism and Pressure Driven Thermal Spin Crossover Phenomenon in [Fe(abpt)2(NCX)2] (X=S, and Se): Synthesis,Structure and Magnetic Properties
2002
The monomeric compounds [Fe(abpt 2(NCX)2(X = S (1), Se (2) and abpt = 4-amino- 3,5-bis(pyridin-2-yl)-1,2,4-triazole) have been synthesized and characterized. They crystallize in the monoclinic P21/n space group with a = 11.637(2) A, b = 9.8021(14) A, c = 12.9838(12) A, β = 101.126(14)°, and Z=2 for 1, and a= 11.601(2) A, b = 9.6666(14) A, c = 12.883(2) A, β = 101.449(10)°, and Z = 2 for 2. The unit cell contains a pair mononuclear [Fe(abpt)2(NCX)21 units related by a center of symmetry. Each iron atom, located at a molecular inversion center, is in a distorted octahedral environment. Four of the six nitrogen atoms coordinated to the Fe(II) ion belong to the pyridine-N(1) and triazole-N(2) r…
ChemInform Abstract: Crystal Structure of the Microwave Dielectric Resonator Ba2Ti9O20.
1983
A single-crystal X-ray study of dibarium nonatitanate, Ba2Ti9O20, yielded the triclinic space group P 1 with a=0.7471(1), b= 1.4081(2), c= 1.4344(2) nm, α=89.94(2)°, β= 79.43(2)°, γ= 84.45(2)°, V = 1.476 nm3 Z = 4, and Dx= 4.61 Mg/m3. A refinement of atomic coordinates and isotropic thermal parameters led to a residual of 0.03. The structure consists of hexagonally closest-packed layers of Ba and O atoms in the sequence (hch)3. All Ti atoms reside in octahedral interstices of this closest packing. The various Ti coordination octahedra share only edges and corners with each other. One-half of the Ba atoms is twelve-coordinated by oxygen atoms, the other half is eleven-coordinated.
Structural characterization, thermal, dielectric and vibrational properties of tris(allylammonium) hexabromoantimonate(III), (C3H5NH3)3SbBr6
2010
Abstract The novel inorganic–organic hybrid material, allylammonium hexabromoantimonate(III), (C3H5NH3)3SbBr6, has been synthesized and its structure has been determined by means of the single-crystal X-ray diffraction studies at five temperatures (273, 248, 220, 170 and 100 K). At room temperature the compound crystallizes in the monoclinic space group, C2/m. Its crystal structure is composed of the discrete SbBr 6 3 - anions and three non-equivalent allylammonium, (C3H5NH3)+, cations. In (C3H5NH3)3SbBr6 three solid–solid structural phase transitions are detected: a continuous one at 260/256 K (on heating–cooling) from phase I to II, a discontinuous one at 227/208 K (II→III) and another di…