scholarly journals Reply to comment on Couzi et al . (2018): a phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds

2019 ◽  
Vol 6 (8) ◽  
pp. 190518 ◽  
Author(s):  
Kirsten Christensen ◽  
P. Andrew Williams ◽  
Rhian Patterson ◽  
Benjamin A. Palmer ◽  
Michel Couzi ◽  
...  
Keyword(s):  
Phase Ii ◽  
Phenomenological Model ◽  
Inclusion Compounds ◽  
Phase Iii ◽  
X Ray Diffraction ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Full Support ◽  
Link Type ◽  
Urea Inclusion

In a recent paper (Couzi et al. 2018 R. Soc. open sci. 5 , 180058. ( doi:10.1098/rsos.180058 )), we proposed a new phenomenological model to account for the I↔II↔“III” phase sequence in incommensurate n -alkane/urea inclusion compounds, which represents an alternative interpretation to that proposed in work of Toudic et al. In a Comment (Toudic et al. 2019 R. Soc. open sci. 6 , 182073. ( doi:10.1098/rsos.182073 )), Toudic et al. have questioned our assignment of the superspace group of phase II of n -nonadecane/urea, which they have previously assigned, based on a (3 + 2)-dimensional superspace, as C222 1 (00 γ )(10 δ ). In this Reply, we present new results from a comprehensive synchrotron single-crystal X-ray diffraction study of n -nonadecane/urea, involving measurements as a detailed function of temperature across the I↔II↔“III” phase transition sequence. Our results demonstrate conclusively that “main reflections” ( h, k, l , 0) with h+k odd are observed in phase II of n -nonadecane/urea (including temperatures in phase II that are just below the transition from phase I to phase II), in full support of our assignment of the (3+1)-dimensional superspace group P2 1 2 1 2 1 (00 γ ) to phase II. As our phenomenological model is based on phase II and phase “III” of this incommensurate material having the same (3+1)-dimensional superspace group P2 1 2 1 2 1 (00 γ ), it follows that the new X-ray diffraction results are in full support of our phenomenological model.

Structural properties of the guest species in diacyl peroxide/urea inclusion compounds: an X-ray diffraction investigation

1990 ◽  
Vol 431 (1882) ◽  
pp. 245-269 ◽  
Keyword(s):  
Single Crystal ◽  
Structural Properties ◽  
Inclusion Compounds ◽  
X Ray Diffraction ◽  
Channel Axis ◽  
Guest Molecules ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Diacyl Peroxide ◽  
Urea Inclusion

In this paper we report single crystal X-ray diffraction studies of urea inclusion compounds containing diacyl peroxides (dioctanoyl peroxide (OP), diundecanoyl peroxide (UP), lauroyl peroxide (LP)) as the guest component. In these inclusion compounds, the host (urea) molecules crystallize in a hexagonal structure that contains linear, parallel, non-intersecting channels (tunnels). The guest (diacyl peroxide) molecules are closely packed inside these channels with a periodic repeat distance that is incommensurate with the period of the host structure along the channel axis. Furthermore, there is pronounced inhomogeneity within the guest structure: within each single crystal, there are regions in which the guest molecules are three-dimensionally ordered, and other regions in which they are only one-dimensionally ordered (along the channel axis). Although it has not proven possible to ‘determine’ the guest structures in the conventional sense, substantial information concerning their average periodicities and their orientational relationships with respect to the host has been deduced from single crystal X-ray diffraction photographs recorded at room temperature. For OP/urea, UP/urea and LP/urea, the guest structure in the three-dimensionally ordered regions is monoclinic, and six types of domain of this monoclinic structure can be identified within each single crystal. The relative packing of diacyl peroxide molecules is the same in each domain, and the different domains are related by 60° rotation about the channel axis. For each of these inclusion compounds, the offset between the ‘heights’ of the guest molecules in adjacent channels is the same ( ca . 4.6 Å (4.6 x 10 -10 m)) within experimental error, suggesting that the relative interchannel packing of the guest molecules is controlled by a property of the diacyl peroxide group. In addition to revealing these novel structural properties, the work discussed in this paper has more general relevance concerning the measurement and interpretation of single crystal X-ray diffraction patterns that are based on more than one three-dimensionally periodic reciprocal lattice. Seven separate reciprocal lattices are required to rationalize the complete X-ray diffraction pattern from each diacyl peroxide/urea crystal studied here.

scholarly journals A phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds

2018 ◽  
Vol 5 (6) ◽  
pp. 180058 ◽  
Author(s):  
Michel Couzi ◽  
François Guillaume ◽  
Kenneth D. M. Harris
Keyword(s):  
Structural Properties ◽  
Phenomenological Model ◽  
Inclusion Compounds ◽  
Structural Phase ◽  
Temperature Phase ◽  
Coupling Mechanism ◽  
Repeat Distance ◽  
Guest Molecules ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion

n -Alkane/urea inclusion compounds are crystalline materials in which n -alkane ‘guest’ molecules are located within parallel one-dimensional ‘host’ tunnels formed by a helical hydrogen-bonded arrangement of urea molecules. The periodic repeat distance of the guest molecules along the host tunnels is incommensurate with the periodic repeat distance of the host substructure. The structural properties of the high-temperature phase of these materials (phase I), which exist at ambient temperature, are described by a (3 + 1)-dimensional superspace. Recent publications have suggested that, in the prototypical incommensurate composite systems, n -nonadecane/urea and n -hexadecane/urea, two low-temperature phases II and ‘III’ exist and that one or both of these phases are described by a (3 + 2)-dimensional superspace. We present a phenomenological model based on symmetry considerations and developed in the frame of a pseudo-spin–phonon coupling mechanism, which accounts for the mechanisms responsible for the I ↔ II ↔ ‘III’ phase sequence. With reference to published experimental data, we demonstrate that, in all phases of these incommensurate materials, the structural properties are described by (3 + 1)-dimensional superspace groups. Around the temperature of the II ↔ ‘III’ transition, the macroscopic properties of the material are not actually associated with a phase transition, but instead represent a ‘crossover’ between two regimes involving different couplings between relevant order parameters.

scholarly journals Orientational disorder and phase transitions in crystals of (NH4)2NbOF5

2008 ◽  
Vol 64 (5) ◽  
pp. 527-533 ◽  
Author(s):  
Anatoly A. Udovenko ◽  
Natalia M. Laptash
Keyword(s):  
Phase Transitions ◽  
Phase Ii ◽  
Central Atom ◽  
Crystal Form ◽  
Partial Ordering ◽  
Phase Iii ◽  
X Ray Diffraction ◽  
Dynamic Nature ◽  
Two Phase ◽  
X Ray

Ammonium oxopentafluoroniobate, (NH4)2NbOF5, was synthesized in a single-crystal form and the structures of its different phases were determined by X-ray diffraction at three temperatures: phase (I) at 297 K, phase (II) at 233 K and phase (III) at 198 K. The distorted [NbOF5]2− octahedra are of similar geometry in all three structures, with the central atom shifted towards the O atom. The structure of (I) is disordered, with three spatial orientations of the [NbOF5]2− octahedron related by a jump rotation around the pseudo-threefold local axis such that the disorder observed is of a dynamic nature. As the temperature decreases, the compound undergoes two phase transitions. The first is accompanied by full anionic ordering and partial ordering of the ammonium groups (phase II). The structure of (III) is completely ordered. The F and O atoms in the structures investigated were identified via the Nb—X (X = O and F) distances. The crystals of all three phases are twinned.

scholarly journals High-Pressure Behaviors of Ag2S Nanosheets: An in Situ High-Pressure X-Ray Diffraction Research

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1640
Author(s):  
Ran Liu ◽  
Bo Liu ◽  
Quan-Jun Li ◽  
Bing-Bing Liu
Keyword(s):  
High Pressure ◽  
Phase I ◽  
Phase Ii ◽  
Structural Phase ◽  
Phase Iii ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Phase ◽  
Ag2s Nanoparticles

An in situ high-pressure X-ray diffraction study was performed on Ag2S nanosheets, with an average lateral size of 29 nm and a relatively thin thickness. Based on the experimental data, we demonstrated that under high pressure, the samples experienced two different high-pressure structural phase transitions up to 29.4 GPa: from monoclinic P21/n structure (phase I, α-Ag2S) to orthorhombic P212121 structure (phase II) at 8.9 GPa and then to monoclinic P21/n structure (phase III) at 12.4 GPa. The critical phase transition pressures for phase II and phase III are approximately 2–3 GPa higher than that of 30 nm Ag2S nanoparticles and bulk materials. Additionally, phase III was stable up to the highest pressure of 29.4 GPa. Bulk moduli of Ag2S nanosheets were obtained as 73(6) GPa for phase I and 141(4) GPa for phase III, which indicate that the samples are more difficult to compress than their bulk counterparts and some other reported Ag2S nanoparticles. Further analysis suggested that the nanosize effect arising from the smaller thickness of Ag2S nanosheets restricts the relative position slip of the interlayer atoms during the compression, which leads to the enhancing of phase stabilities and the elevating of bulk moduli.

Diffuse and satellite scattering in urea inclusion compounds with various alkane molecules

1996 ◽  
Vol 211 (4) ◽  
Author(s):  
Th. Weber ◽  
H. Boysen ◽  
M. Honal ◽  
F. Frey ◽  
R. B. Neder
Keyword(s):  
Inclusion Compounds ◽  
Diffuse Scattering ◽  
Room Temperature ◽  
Guest Molecules ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion

AbstractX-ray diffuse scattering phenomena and satellite reflections in urea inclusion compounds with guest molecules of varying lengths (tridecane, tetradecane, pentadecane, heptadecane and a mixture of pentadecane and hexadecane) were investigated between room temperature and 30 K. It was found that diffuse

Definitive Structural Characterization of the Conventional Low-Temperature Host Structure in Urea Inclusion Compounds

1997 ◽  
Vol 53 (5) ◽  
pp. 822-830 ◽  
Author(s):  
L. Yeo ◽  
K. D. M. Harris
Keyword(s):  
Low Temperature ◽  
Inclusion Compounds ◽  
Temperature Phase ◽  
Temperature Structure ◽  
Tunnel Structure ◽  
X Ray Diffraction ◽  
Guest Molecules ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion ◽  
Low Temperature Phase

Structural properties of the 1,10-dibromodecane/urea and 1,12-dibromododecane/urea inclusion compounds have been determined by single-crystal X-ray diffraction for both the high- and low-temperature phases. In the high-temperature phase both inclusion compounds have the conventional hexagonal urea tunnel structure, with substantial orientational disorder of the guest molecules. In the low-temperature phase the urea tunnel structure distorts to an orthorhombic structure, based on a distorted form of the orthohexaganol cell of the high-temperature structure and with the loss of the C centre. Within this tunnel structure there is evidence that the guest molecules have a narrow distribution of orientations (with respect to rotation about the tunnel axis) and the preferred orientation of the guest molecules correlates well with the observed distortion of the host tunnel. This represents the first accurate and reliable report of the conventional low-temperature structure of urea inclusion compounds. Previous powder X-ray diffraction studies have confirmed that the host structure in the low-temperature phase of 1,10-dibromodecane/urea is the same as that in the low-temperature phase of the alkane/urea inclusion compounds.

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