A low temperature phase of (NH4)2TeBr6

1969 ◽  
Vol 47 (22) ◽  
pp. 4288-4289 ◽  
Author(s):  
A. K. Das ◽  
I. D. Brown
Keyword(s):  
Low Temperature ◽  
Tetragonal Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Low Temperature Phase

X-Ray diffraction has shown the existence of a low temperature tetragonal phase of (NH4)2TeBr6 having space group P4/mnc(D4h6) with a = 7.501, c = 10.765 Å.

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

X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites

2001 ◽  
Vol 57 (3) ◽  
pp. 221-230 ◽  
Author(s):  
A. Guelylah ◽  
G. Madariaga ◽  
V. Petricek ◽  
T. Breczewski ◽  
M. I. Aroyo ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Mode Analysis ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
New Type ◽  
Low Temperature Phase

The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100–300 K. Using DSC measurements, a phase transition has been detected at 213 K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690 (8), b = 20.136 (2), c = 10.0329 (4) Å, γ = 90.01 (1)°]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds.

Substitutions in Hg-cuprate superconductors

1994 ◽  
Vol 9 (11) ◽  
pp. 2809-2813 ◽  
Author(s):  
V. Kirtikar ◽  
K.K. Singh ◽  
D.E. Morris
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
Magnetization Curve ◽  
Cuprate Superconductors ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lattice Constants ◽  
Superconducting Compounds ◽  
Low Temperature Phase

Several substitutions have been attempted in the Hg layer of the Hg 1212 and 1223 cuprate superconductors. A new series of (Hg,Bi)1212 superconducting compounds has been synthesized. The highest Tc of the series (92 K) is found for the composition (Hg0.67Bi0.33)Sr2(Y0.5Ca0.5)Cu2O7−δ, with lattice constants a = 3.811 Å and c = 12.002 Å. X-ray diffraction and SEM with EDX analysis confirm that Hg is indeed incorporated in the structure. High-pressure oxygenation at 250 bar and 400 °C changes the magnetization curve, adding a second transition at ∼42 K; the 92 K transition remains unchanged. High-pressure oxygenation of Pb-substituted composition of the 1223 system, (Hg0.67Pb0.33)Ba2Ca2Cu3O8 also leads to the formation of low temperature phase with Tc = 67 K. The low Tc phase is associated with the incorporation of extra oxygen, possibly in the Hg layer.

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.

Neutron diffraction study of the orthorhombic low-temperature phase of N2D7I and X-ray investigations of the tetragonal and orthorhombic phases of N2H7I

1993 ◽  
Vol 203 (2) ◽  
Author(s):  
H. J. Berthold ◽  
E. Vonholdt ◽  
R. Wartchow ◽  
T. Vogt
Keyword(s):  
Low Temperature ◽  
Neutron Diffraction ◽  
Diffraction Study ◽  
Tetragonal Phase ◽  
Orthorhombic Phase ◽  
Neutron Diffraction Study ◽  
Temperature Phase ◽  
X Ray ◽  
Low Temperature Phase

AbstractNThe structure of the orthorhombic phase of NThe orthorhombic phase of NThe orthorhombic phase of NThe structure of the tetragonal phase observed only with N

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