Low- and high-temperature structures of neopentylglycol plastic crystal

1993 ◽  
Vol 8 (2) ◽  
pp. 109-117 ◽  
Author(s):  
Dhanesh Chandra ◽  
Cynthia S. Day ◽  
Charles S. Barrett
Keyword(s):  
High Temperature ◽  
Phase Structure ◽  
Binary Systems ◽  
Structural Parameters ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Space Group ◽  
Plastic Crystals ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

Plastic crystals, such as neopentylglycol, 2, 2-dimethyl-1,3-propanediol, that exhibit polymorphic behavior are emerging materials for thermal energy storage. The energy is stored isothermally in the γ phase, FCC, during solid-state phase transformations. This γ phase of NPG has been determined as an orientational disordered phase. The low temperature α phase structure, which is of great significance in the evaluation of lattice expansions and other parameters, was first determined in 1961. However, the reported unit cell dimensions and the intensities of the reflections led to erroneous indexing of the powder patterns in binary systems. The α phase structure is redetermined here as monoclinic, M= 104.15 amu, space group P21/n (an alternate setting of , space group No. 14), a = 5.979(1)Å, b= 10.876(2)Å, c=10.099(2)Å, β=99.78(1)°, V=647.2(2)Å3 at 20°(± 1)C, Dx= 1.069 g cm s−3 for Z=4. In this paper the redetermined structure of the α phase of NPG is presented in projections of the atomic positions, in tables, and in calculated powder pattern and these results are compared with those reported by others. The powder patterns obtained from the Bragg–Brentano diffractometer are compared with our calculated pattern from the single crystal data. The structural parameters of the high temperature phase of NPG as determined by a Guinier diffraction system are also reported.

Mode-crystallography analysis of the crystal structures and the low- and high-temperature phase transitions in Na0.5K0.5NbO3

2015 ◽  
Vol 48 (2) ◽  
pp. 318-333 ◽  
Author(s):  
B. Orayech ◽  
A. Faik ◽  
G. A. López ◽  
O. Fabelo ◽  
J. M. Igartua
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Crystal Structures ◽  
Degrees Of Freedom ◽  
High Temperature Phase ◽  
Structure Evolution ◽  
Internal Space ◽  
Temperature Phase ◽  
Conventional Solid State Reaction ◽  
Space Group

Na0.5K0.5NbO3has been synthesized by the conventional solid-state reaction process. The crystal structures and phase transitions, at low and high temperature, determined from the Rietveld refinements of X-ray and neutron powder diffraction data are reported. The structure evolution of Na0.5K0.5NbO3in the temperature range from 2 to 875 K shows the presence of three phase transitions. The first one, at ∼135 K, is discontinuous from the rhombohedralR3c(No. 161) space group to the room-temperature orthorhombicAmm2 (No. 38) space group; the second is discontinuous from the orthorhombic to the tetragonalP4mmspace group (No. 99) at ∼465 K, and the third is continuous from the tetragonal to the cubic Pm\overline{3}m space group (No. 221) at ∼700 K. The obtained phase-transition sequence isR3c→Amm2 →P4mm→Pm\overline{3}m. No previous studies at low temperature have been carried out on the material with composition Na0.5K0.5NbO3. In the course of the determination of the three experimentally found phases, a novel method of refinement is presented. This is a step forward in the use of the symmetry-adapted modes as degrees of freedom in the refinement process: the parameterization of a direction in the internal space of the, in this case, sole irreducible representation, GM4−, responsible for the symmetry breaking from the parent cubic space group to the polar distorted low-symmetry phases. Eventually, this procedure enables the calculation of the spontaneous polarization.

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.

scholarly journals On the high temperature phase transition in Ba(Zr0.20Ti0.80)O3 ceramic

2017 ◽  
Vol 07 (04) ◽  
pp. 1750025 ◽  
Author(s):  
K. P. Chandra ◽  
A. R. Kulkarni ◽  
K. Prasad
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Lattice Structure ◽  
High Temperature Phase ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Potential Candidate ◽  
Space Group ◽  
Structure Changes ◽  
Temperature Phase Transition

Temperature dependent X-ray diffraction (XRD) and dielectric properties of perovskite Ba(Zr[Formula: see text]Ti[Formula: see text]O3 ceramic prepared using a standard solid-state reaction process is presented. Along with phase transitions at low temperature, a new phase transition at high temperature (873[Formula: see text]C at 20[Formula: see text]Hz), diffusive in character has been found where the lattice structure changes from monoclinic (space group: [Formula: see text] to hexagonal (space group: [Formula: see text]). This result places present ceramic in the list of potential candidate for intended high temperature applications. The AC conductivity data followed hopping type charge conduction and supports jump relaxation model. The experimental value of [Formula: see text][Formula: see text]pC/N was found. The dependence of polarization and strain on electric field at room temperature suggested that lead-free Ba(Zr[Formula: see text]Ti[Formula: see text]O3 is a promising material for electrostrictive applications.

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

scholarly journals Zur Polymorphie von TbCI3/ Polymorphism of TbCl3

1988 ◽  
Vol 43 (8) ◽  
pp. 1023-1028 ◽  
Author(s):  
Harald Gunsilius ◽  
Horst Borrmann ◽  
Arndt Simon ◽  
Werner Urland
Keyword(s):  
High Temperature ◽  
Metastable State ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Space Group

Abstract3 different modifications of TbCl3 were synthesized. TbCl, (UCl3-type), probably in a metastable state, crystallizes in space group P63/m with a = 737.63(2) pm, c = 405.71(2) pm and Z - 2. TbCl3 (PuB3-type) crystallizes in space group Cmcm with a = 384.71(6) pm, b = 1177.37(7) pm. c = 851.77(4) pm and Z = 4. h-TbCl3, the high temperature phase being stable above 790 K. crystallizes in space group P42/mnm with a = 642.51(4) pm, c = 1177.14(18) pm and Z = 4.

Interplay between Anion Rotation and Cation Transport in the Plastic High-Temperature Phase of Sodium Ortho-Phosphate

1998 ◽  
Vol 527 ◽  
Author(s):  
K. Funke ◽  
D. Wilmer ◽  
R. D. Banhatti ◽  
M. Witschas ◽  
R. E. Lechner ◽  
...  
Keyword(s):  
High Temperature ◽  
High Temperature Phase ◽  
Dynamics Simulation ◽  
Temperature Phase ◽  
Present Contribution ◽  
Plastic Crystals ◽  
Quasielastic Neutron ◽  
Quasielastic Neutron Scattering ◽  
Ion Conducting ◽  
A Chain

ABSTRACTThe high-temperature phase of sodium ortho-phosphate, α-Na3PO4, belongs to the class of ion conducting plastic crystals, i.e., it is characterized by a dynamic rotational disorder of its poly-atomic anions and, at the same time, by a considerable translational mobility of its cations. During the past decade, the possibility, nature, and importance of a dynamic interplay between the two kinds of motion have been a subject of continued controversy. Proponents of a strong interplay coined the expression “paddle-wheel mechanism”. In our present contribution we report, for the first time, on the results of dynamic experiments probing the elementary steps of anionic and cationic motion individually. The techniques utilized in this study are coherent quasielastic neutron scattering and high-frequency conductivity spectroscopy, respectively. The data are complemented by an ab-initio molecular-dynamics simulation. Our results provide a view of the movement of anions and cations and of correlations between them. Strong dynamic coupling is detected between the octahedrally coordinated sodium ions and nearby oxygen ions. For translational sodium-ion transport, a chain mechanism appears to be operative.

Structural parameters: Analysis of results

2010 ◽  
Author(s):  
Jenny Pickworth Glusker ◽  
Kenneth N. Trueblood
Keyword(s):  
Crystal Structure ◽  
Structural Parameters ◽  
Three Dimensional ◽  
Molecular Geometry ◽  
Unit Cell ◽  
Space Group ◽  
Cell Dimensions ◽  
Information File ◽  
The Individual ◽  
Unit Cell Dimensions

The results of an X-ray structure analysis are coordinates of the individual, chemically identified atoms in each unit cell, the space group (which gives equivalent positions), and displacement parameters that may be interpreted as indicative of molecular motion and/or disorder. Such data obtained from crystal structure analyses may be incorporated into a CIF or mmCIF (Crystallographic Information File or Macromolecular Crystallographic Information File). These ensure that the results of crystal structure analyses are usefully archived. There are many checks that the crystallographer can make to ensure that the CIF or mmCIF file is correctly informative. For example, the automated validation program PLATON (Spek, 2003) checks that all data reported are up to the standards required for publication by the International Union of Crystallography. It does geometrical calculations on the structure, illustrates the results, finds if any symmetry has been missed, investigates any twinning, and checks if the structure has already been reported. We now review the ways in which these atomic parameters can be used to obtain a three-dimensional vision of the entire crystal structure. When molecules crystallize in an orthorhombic, tetragonal, or cubic unit cell it is reasonably easy to build a model using the unit-cell dimensions and fractional coordinates, because all the interaxial angles are 90◦. However, the situation is more complicated if the unit cell contains oblique axes and it is often simpler to convert the fractional crystal coordinates to orthogonal coordinates before calculating molecular geometry. The equations for doing this for bond lengths, interbond angles, and torsion angles are presented in Appendix 12. If the reader wishes to compute interatomic distances directly, this is also possible if one knows the cell dimensions (a, b, c, ∝ , β , γ ,), the fractional atomic coordinates (x, y, z for each atom), and the space group.

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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