scholarly journals The structure of the aluminium-abundant γ-brass-type Al8.6Mn4.4

IUCrData ◽  
2021 ◽  
Vol 6 (9) ◽  
Author(s):  
Qifa Hu ◽  
Bin Wen ◽  
Changzeng Fan
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Structure Analysis ◽  
Site Occupancy ◽  
Initial Composition ◽  
Special Position ◽  
Space Group ◽  
Type Phase ◽  
Centrosymmetric Space Group ◽  
Acta Mater

An aluminium-abundant Al8Mn5/γ-brass-type intermetallic with formula Al8.6Mn4.4, which is isotypic with γ-Al8Cr5 and γ-Al8V5, was discovered by high-temperature sintering of an Al/Mn mixture with initial composition Al2Mn. Structure analysis revealed that one special position (Wyckoff site 18h in space group R\overline{3}m) is shared by Al and Mn, with refined site occupancy factors of 0.7 and 0.3, respectively. The present low-temperature Al8Mn5-type phase crystallizes in the centrosymmetric space group R\overline{3}m (No. 166), rather than R3m (No. 160) as previously reported for the same intermetallic characterized by TEM measurements [Zeng et al. (2018). Acta Mater. 153, 364–376].

Omega-related phases in a Ti-Al-Nb alloy

1989 ◽  
Vol 47 ◽  
pp. 324-325
Author(s):  
Leonid A. Bendersky ◽  
William J. Boettinger
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Phase Equilibria ◽  
Chemical Order ◽  
Space Group ◽  
Low Temperature Annealing ◽  
Type Phase ◽  
B2 Phase ◽  
B2 Structure ◽  
Displacive Type

Study of phase equilibria in the Ti-Al-Nb system is often complicated by the possibility of rapid ordering reactions of a chemical or displacive type during cooling from high temperatures. In the present study we have investigated the decomposition of the high temperature B2 phase of composition Ti-37.5at%Al-12.5at%Nb into “omega-type” phases during either cooling or low temperature annealing. Formation of an “omega-type” phase from the high temperature B2 matrix of composition Ti-27.8at%Al-11.7at%Nb was observed previously by [1]. If the “omega-type” phase forms by pure displacive ordering, i.e. by collapse of (111) plane pairs of the B2 phase, the resulting structure will be as shown in Fig. 1a (termed ω′). The chemical order of the ω′ phase is directly inherited from the B2 structure. The space group of the ω′ phase is P3ml (#164). The same authors suggested a secondary transformation of the ω′ phase to another omega-type phase with the B82 structure shown in Fig.1b The space group for the B82 structure is hexagonal P63/mmc (#194) with reflection conditions such that the 1100 reflection is present, but the 0001 (or 000ℓ,ℓ=2n+l) is absent.

Structural chemistry of NaCoPO4

1996 ◽  
Vol 52 (3) ◽  
pp. 440-449 ◽  
Author(s):  
R. Hammond ◽  
J. Barbier
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Large Family ◽  
X Ray Diffraction ◽  
Tetrahedral Framework ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Tetrahedral Sites ◽  
Bond Valence Analysis

Sodium cobalt phosphate, NaCoPO4, occurs as two different polymorphs which transform reversibly at 998 K. The crystal structures of both polymorphs have been determined by single-crystal X-ray diffraction. The low-temperature form α-NaCoPO4 crystallizes in the space group Pnma with cell parameters: a = 8.871 (3), b = 6.780 (3), c = 5.023 (1) Å, and Z = 4 [wR(F 2) = 0.0653 for all 945 independent reflections]. The α-phase contains octahedrally coordinated Co and Na atoms and tetrahedrally coordinated P atoms, and is isostructural with maracite, NaMnPO4. The structure of high-temperature β-NaCoPO4 is hexagonal with space group P65 and cell parameters: a = 10.166 (1), c = 23.881 (5) Å, and Z = 24 [wR(F 2) = 0.0867 for 4343 unique reflections]. The β-phase belongs to the large family of stuffed tridymites, with the P and Co atoms occupying tetrahedral sites and the Na atoms located in the cavities of the tetrahedral framework. The long c axis corresponds to a 3 × superstructure of the basic tridymite framework (c ≃ 8 Å) and is caused by the displacement of the Na atoms, tetrahedral tilts and strong distortions of the CoO4 tetrahedra. A bond-valence analysis of these phases reveals that the polymorphism in NaCoPO4 is due in part to over-/underbonding of the Na atom in the low-/high-temperature structures, respectively.

scholarly journals Über die Strukturen der CuZrF6-Modifikationen - Neutronenbeugungsuntersuchungen an den Kristallpulvern / A Neutron Diffraction Study on the Modifications of CuZrF6

1978 ◽  
Vol 33 (3) ◽  
pp. 268-274 ◽  
Author(s):  
V. Propach ◽  
F. Steffens
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Experimental Evidence ◽  
Neutron Diffraction Study ◽  
Three Dimensions ◽  
Space Group ◽  
Powder Samples ◽  
Jahn Teller ◽  
Jahn Teller Effect

Abstract The structures of two modifications of CuZrF6 by means of neutron diffraction on powder samples in the temperature range from 298-560 K are reported. All modifications consist of octahedra, which share corners in three dimensions and which are centered alternately by Cu2+ or Zr4+. The high temperature α-modification crystallizes in space group Fm3 (No. 202) with α = 7.939 Å. There is experimental evidence, that the CuFe-octahedra are distorted by a static Jahn-Teller-effect. The space group P1̄ (No. 2) with Z = 2 is proposed for the low-temperature γ-modification.

Irreversible single-crystal to polycrystal and reversible single-crystal to single-crystal phase transformations in cyanurates

2001 ◽  
Vol 57 (6) ◽  
pp. 791-799 ◽  
Author(s):  
Menahem Kaftory ◽  
Mark Botoshansky ◽  
Moshe Kapon ◽  
Vitaly Shteiman
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Low Temperature ◽  
Single Crystal ◽  
High Temperature Phase ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Space Group ◽  
Reversible Phase ◽  
Low Temperature Phase

4,6-Dimethoxy-3-methyldihydrotriazine-2-one (1) undergoes a single-crystal to single-crystal reversible phase transformation at 319 K. The low-temperature phase crystallizes in monoclinic space group P21/n with two crystallographically independent molecules in the asymmetric unit. The high-temperature phase is obtained by heating a single crystal of the low-temperature phase. This phase is orthorhombic, space group Pnma, with the molecules occupying a crystallographic mirror plane. The enthalpy of the transformation is 1.34 kJ mol−1. The small energy difference between the two phases and the minimal atomic movement facilitate the single-crystal to single-crystal reversible phase transformation with no destruction of the crystal lattice. On further heating, the high-temperature phase undergoes methyl rearrangement in the solid state. 2,4,6-Trimethoxy-1,3,5-triazine (3), on the other hand, undergoes an irreversible phase transformation from single-crystal to polycrystalline material at 340 K with an enthalpy of 3.9 kJ mol−1; upon further heating it melts and methyl rearrangement takes place.

35Cl NQR and Structural Studies of Chloroacetanilides C6H3Cl2NHCOCH3-xClx, 1 ≤ x ≤ 3

1992 ◽  
Vol 47 (1-2) ◽  
pp. 160-170
Author(s):  
Dirk Groke ◽  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Temperature Dependence ◽  
Phenyl Group ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Chlorine Atoms ◽  
Space Group ◽  
Low Temperature Phase

AbstractThe temperature dependence of 35Cl NQR frequencies and the phase transition behaviour of chloroacetanilides (N-[2,6-dichlorophenyl]-2-chloroacetamide, -2,2-dichloroacetamide, -2,2,2-trichloroacetamide) were investigated. The crystal structure determination of N-[2,6-dichlorophenyl]- 2-chloroacetamide leads to the following: a = 1893.8 pm, b = 1110.7 pm, c = 472.1 pm, space group P212121 = D24 with Z = 4 molecules per unit cell. The arrangement of the molecules and their geometry is comparable to the high temperature phase of the acetyl compound N-[2,6-dichlorophenyl]- acetamide. For N-[2,6-diclorophenyl]-2,2,2-trichloroacetamide it was found: a = 1016.6 pm, b = 1194.3 pm, c = 1006.7 pm, ß= 101.79°, space group P21/c = C52h, Z = 4. The structure is similar to the low temperature phase of N-[2,6-dichlorophenyl]-acetamide. Parallelism between the temperature dependence of the 35C1 NQR lines of the CCl3 group and the X-ray diffraction results concerning the different behaviour of the chlorine atoms was observed. The structures of the compounds show intermolecular hydrogen bonding of the N - H • • • O - C type. The phenyl group and the HNCO function are nearly planar. A bleaching out of several 35Cl NQR lines at a temperature far below the melting point of the substances was observed. The different types of chlorine atoms (aromatic, chloromethyl) can be distinguished by their temperature coefficients of the 35Cl NQR frequencies. All the resonances found show normal "Bayer" temperature behaviour. N-[2,6-dichlorophenyl]-2,2-diehloroacetamide shows several solid phases. One stable low temperature phase and an instable high temperature phase (at room temperature) were observed. The different phases were detected by means of 35Cl NQR spectroscopy and thermal analysis

The low-temperature crystal structure of the multiferroic melilite Ca2CoSi2O7

2016 ◽  
Vol 72 (1) ◽  
pp. 126-132 ◽  
Author(s):  
Andrew Sazonov ◽  
Vladimir Hutanu ◽  
Martin Meven ◽  
Georg Roth ◽  
István Kézsmárki ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Low Temperature ◽  
Structural Parameters ◽  
Theoretical Description ◽  
Temperature Structure ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Precise Knowledge ◽  
Commensurate Phase

In the antiferromagnetic ground state, belowTN≃ 5.7 K, Ca2CoSi2O7exhibits strong magnetoelectric coupling. For a symmetry-consistent theoretical description of this multiferroic phase, precise knowledge of its crystal structure is a prerequisite. Here we report the results of single-crystal neutron diffraction on Ca2CoSi2O7at temperatures between 10 and 250 K. The low-temperature structure at 10 K was refined assuming twinning in the orthorhombic space groupP21212 with a 3 × 3 × 1 supercell [a= 23.52 (1),b= 23.52 (1),c= 5.030 (3) Å] compared with the high-temperature normal state [tetragonal space group P\overline {4}2_{1}m,a=b≃ 7.86,c≃ 5.03 Å]. The precise structural parameters of Ca2CoSi2O7at 10 K are presented and compared with the literature X-ray diffraction results at 130 and 170 K (low-temperature commensurate phase), as well as at ∼ 500 K (high-temperature normal phase).

Design and synthesis of Ba3SiSe5 with suitable birefringence modulated via MIV atoms in Ba-MIV-Q (MIV = Si, Ge; Q = S, Se) system

2021 ◽  
Author(s):  
Huanhuan Cheng ◽  
Abudukadi Tudi ◽  
Peng Wang ◽  
Kewang Zhang ◽  
Zhihua Yang ◽  
...  
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Solid State Method ◽  
Orthorhombic System ◽  
Space Group ◽  
Design And Synthesis ◽  
Centrosymmetric Space Group ◽  
System P ◽  
State Method

A new ternary Ba-based selenide, Ba3SiSe5, was synthesized by high-temperature solid-state method. It crystalizes in the centrosymmetric space group Pnma (No. 62) of the orthorhombic system. The structure of the...

An explanation for the origin of hemihedrism in wulfenite: the single-crystal structures of I4̄1/a and I4̄ tungstenian wulfenites

2000 ◽  
Vol 64 (6) ◽  
pp. 1057-1062 ◽  
Author(s):  
D. E. Hibbs ◽  
C. M. Jury ◽  
P. Leverett ◽  
I. R. Plimer ◽  
P. A. Williams
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
San Francisco ◽  
Analytical Data ◽  
Site Occupancy ◽  
Unit Cell ◽  
Special Position ◽  
Space Group ◽  
X Ray ◽  
Single Crystal Structures

AbstractThe single-crystal X-ray structure of tungstenian wulfenite-I41/a containing 10 mol.% WO3 from the San Francisco mine, Sonora, Mexico, space group I41/a, a = 5.436(2), c = 12.068(8)Å and Z = 4, has been refined to R = 0.052. The Mo and W are disordered over special position 4a (0,0,0) in the lattice. Tungstenian wulfenite-I4̄ (‘chillagite’) from the Christmas Gift mine, Chillagoe, Queensland, Australia (Museum of Victoria specimen M16934), crystallizes in the closely related tetragonal space group I4̄, with a = 5.441(1), c = 12.068(6) Å and Z = 4. The structure was refined to R = 0.038. Refined site occupancy factors show that Mo and W are not distributed equally over the two crystallographically independent Mo/W positions, being 0.136(2) for Mo and 0.114(2) for W in special position 2a (0,0,0) and 0.184(2) for Mo and 0.066(2) for W in special position 2c (0,Ý,Ü). These give a composition corresponding to wulfenite64stolzite36, in agreement with analytical data. The Mo/W distributions in the unit cell provide one explanation for the origin of hemihedrism in the wulfenite-stolzite series.

Synthesis, Characterization and Theoretical Investigation of the New Chalcohalide Ba4GaS4F3

2021 ◽  
Author(s):  
Hongbo Gao ◽  
Ruijiao Chen ◽  
kewang zhang ◽  
Ailijiang Abudurusuli ◽  
Kangrong Lai ◽  
...  
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Theoretical Investigation ◽  
Solid State Reaction ◽  
Space Group ◽  
Centrosymmetric Space Group

A new fluorine-contained chalcohalide, Ba4GaS4F3, has been synthesized by conventional high-temperature solid-state reaction. The compound crystallizes in the centrosymmetric space group I41/a with a = b = 16.628 (5) Å,...

Polymorphism of Li2Zn3

2012 ◽  
Vol 68 (1) ◽  
pp. 34-39 ◽  
Author(s):  
Volodymyr Pavlyuk ◽  
Ihor Chumak ◽  
Helmut Ehrenberg
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Tight Binding ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Space Group ◽  
Temperature Modification ◽  
Rhombic Dodecahedra ◽  
Low Temperature Phase

Crystal structures of low- and high-temperature modifications of the binary phase Li2Zn3 were determined by single-crystal X-ray diffraction techniques. The low-temperature modification is a disordered variant of Li5Sn2, space group R\bar 3m (No. 166). The high-temperature modification crystallizes as an anti-type to Li5Ga4, space group P\bar 3m1 (No. 164). Two polymorphs can be described as derivative structures to binary Li5Ga4, Li5Sn2, Li13Sn5, Li8Pb3, CeCd2 and CdI2 phases which belong to class 2 with the parent W-type in Krypyakevich's classification. All atoms in both polymorphs are coordinated by rhombic dodecahedra (coordination number CN = 14) like atoms in related structures. The Li2Zn2.76 (for the low-temperature phase) and Li2Zn2.82 (for the high-temperature phase) compositions were obtained after structure refinements. According to electronic structure calculations using the tight-binding–linear muffin-tin orbital–atomic spheres approximations (TB–LMTO–ASA) method, strong covalent Sn—Sn and Ga—Ga interactions were established in Li5Sn2 and Li5Ga4, but no similar Zn—Zn interactions were observed in Li2Zn3.

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