Redetermination of the structure and dielectric properties of bis(thiourea) pyridinium iodide – a new ferroelectric inclusion compound

The crystal structure of bis(thiourea) pyridinium iodide (T2PyI) was previously determined at 295 and 110 K [Prout, Heyes, Dobson, McDaid, Maris, Mueller & Seaman (2000). Chem. Mater. 12, 3561–3569] and the two phases were described in the space groups Cmcm and P21 cn, respectively. Because differential scanning calorimetry revealed two phase transitions, at 161 and 141 K, a redetermination of the structure of T2pyI at 295, 155 and 110 K has been undertaken, and the following sequence of space groups obtained: Cmcm (I) → C2cm (II) → P21 cn (III). The high- (I) and low-temperature (III) phases confirmed the results reported in the previous study. In the new intermediate phase II, the mirror plane perpendicular to the x axis vanishes and the crystal structure loses the centre of symmetry. In phases I and II the pyridinium cations are strongly dynamically disordered, while in the low-temperature phase III the cations are well ordered. In all three phases the thiourea–iodine hydrogen-bonded sublattice is very well ordered. Dielectric measurements show that the intermediate and low-temperature phases are ferroelectric and that 161 K is the Curie point of a new ferroelectric crystal.

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Interrelation between Molecular Motions and Phase Transitions in Monomethylammonium Perchlorate. A Study by DSC, Proton, and Deuteron NMR

Zeitschrift für Naturforschung A ◽

10.1515/zna-1985-0611 ◽

1985 ◽

Vol 40 (6) ◽

pp. 602-610 ◽

Cited By ~ 19

Author(s):

S. Jurga ◽

H. W. Spiess

Keyword(s):

Low Temperature ◽

Hydrogen Bonds ◽

Phase Ii ◽

Intermediate Phase ◽

Relaxation Times ◽

Spin Lattice Relaxation ◽

Phase Iii ◽

Temperature Phase ◽

Molecular Motions ◽

Scanning Calorimetry

Differential scanning calorimetry, the temperature dependence of proton and deuteron lineshapes and spin-lattice relaxation times are reported for the isotopic species CH3NH3ClO4, CD3NH3ClO4 and CH3ND3ClO4 of monomethylammonium Perchlorate. The data confirmed the existence of three different phase modifications in monomethylammonium Perchlorate and its selectively deuterated analogues. In addition they were used to identify the molecular motions occurring in the respective phases and to determine their activation parameters. In the low temperature phase III, stable below 320 K. the CH3 and NH3 groups reorient about their threefold symmetry axes C3 with different frequencies. In the low-temperature range of this phase the deuteron quadrupole coupling constant indicates N - H ... O hydrogen bonds between the monomethylammonium and the Perchlorate ions. In the intermediate phase II, between 320 K and 451 K for CH3NH3ClO4 and CD3NH3ClO4 and 320 K and 437 K for CH3ND3ClO4 , the methylammonium ions reorient about an axis inclined at an angle of 18 degrees to the C3 axis. The analysis of the entropy changes, associated with the III- II transitions indicates that the ClO4− ions have a large motional freedom in phase II, presumably because of breaking or weakening of N - H . . . O hydrogen bonds. In phase I the monomethylammonium ions undergo isotropic motion along with translational diffusion between different sites of the primitive cubic unit cell.

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Structural phase transition and hydrogen ordering of TlH2PO4 at low temperature

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768106018222 ◽

2006 ◽

Vol 62 (5) ◽

pp. 719-728 ◽

Cited By ~ 16

Author(s):

I. H. Oh ◽

M. Merz ◽

S. Mattauch ◽

G. Heger

Keyword(s):

Crystal Structure ◽

Phase Transition ◽

Low Temperature ◽

Structural Phase ◽

Crystal Structure Analysis ◽

Temperature Phase ◽

Structure Model ◽

Triclinic Space Group ◽

Space Groups ◽

Low Temperature Phase

The crystal structure of TlH2PO4 (TDP) has been studied at low temperature. The lattice parameters were derived from high-resolution X-ray powder diffraction in the temperature range between 8 and 300 K. A detailed crystal structure analysis of the antiferroelectric low-temperature phase TDP-III has been performed based on neutron diffraction data measured at 210 K on a twinned crystal consisting of two domain states. The structure model in the triclinic space group P\bar 1 is characterized by a complete ordering of all the H atoms in the asymmetric O—H...O hydrogen bonds. The phase transition from the ferroelastic TDP-II to the antiferroelectric TDP-III phase at 229.5 ± 0.5 K is only slightly of first order and shows no detectable hysteresis effects. Its mechanism is driven by the hydrogen ordering between the partially ordered TDP-II state and the completely ordered TDP-III state. The polymorphism of TDP and the fully deuterated TlD2PO4 (DTDP) is presented in the form of group–subgroup relations between the different space groups.

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Low-temperature structure of V6O13

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768103023437 ◽

2003 ◽

Vol 59 (6) ◽

pp. 747-752 ◽

Cited By ~ 26

Author(s):

Jonas Höwing ◽

Torbjörn Gustafsson ◽

John O. Thomas

Keyword(s):

Low Temperature ◽

Mirror Plane ◽

Temperature Phase ◽

Temperature Structure ◽

X Ray Diffraction ◽

Scanning Calorimetry ◽

Acta Cryst ◽

Lithium Polymer Batteries ◽

Space Group ◽

Dsc Measurements

The structure of the transition metal oxide V6O13, a potential cathode material in lithium-polymer batteries, has been studied at 95 K using single-crystal X-ray diffraction (XRD). A phase transition has been determined by differential scanning calorimetry (DSC) measurements to occur at 153 K, with a heat of transition of −1.98 kJ mol−1. In this low-temperature phase, the V and O atoms move by up to 0.21 Å out of the mirror plane they occupy in the room-temperature structure. It is concluded that the earlier reported space group P21/a [Kawada et al. (1978). Acta Cryst. B34, 1037–1039] is incorrect and that a more appropriate choice of space group is Pc.

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FIRST PRINCIPLE MODELING OF THE LITHIUM IMIDE CRYSTAL STRUCTURE IN A LOW-TEMPERATURE PHASE

Журнал структурной химии ◽

10.26902/jsc_id61804 ◽

2020 ◽

Vol 61 (10) ◽

Keyword(s):

Crystal Structure ◽

Low Temperature ◽

Temperature Phase ◽

First Principle ◽

Lithium Imide ◽

Low Temperature Phase

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Crystal chemistry of transition metal diarsenates M 2As2O7 (M = Mn, Co, Ni, Zn): variants of the thortveitite structure

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768110040802 ◽

2010 ◽

Vol 66 (6) ◽

pp. 603-614 ◽

Cited By ~ 12

Author(s):

Matthias Weil ◽

Berthold Stöger

Keyword(s):

Crystal Structure ◽

Low Temperature ◽

Transition Metal ◽

Basic Structure ◽

Structure Type ◽

Ambient Conditions ◽

Modulated Structure ◽

Triclinic Crystal System ◽

Space Groups ◽

Unit Cells

The structures of the 3d divalent transition-metal diarsenates M 2As2O7 (M = Mn, Co, Ni, Zn) can be considered as variants of the monoclinic (C2/m) thortveitite [Sc2Si2O7] structure type with a ≃ 6.7, b ≃ 8.5, c ≃ 4.7 Å, α ≃ 90, β ≃ 102, γ ≃ 90° and Z = 2. Co2As2O7 and Ni2As2O7 are dimorphic. Their high-temperature (β) polymorphs adopt the thortveitite aristotype structure in C2/m, whereas their low-temperature (α) polymorphs are hettotypes and crystallize with larger unit cells in the triclinic crystal system in space groups P\bar 1 and P1, respectively. Mn2As2O7 undergoes no phase transition and likewise adopts the thortveitite structure type in C2/m. Zn2As2O7 has an incommensurately modulated crystal structure [C2/m(α,0,γ)0s] with q = [0.3190 (1), 0, 0.3717 (1)] at ambient conditions and transforms reversibly to a commensurately modulated structure with Z = 12 (I2/c) below 273 K. The Zn phase resembles the structures and phase transitions of Cr2P2O7. Besides descriptions of the low-temperature Co2As2O7, Ni2As2O7 and Zn2As2O7 structures as five-, three- and sixfold superstructures of the thortveitite-type basic structure, the superspace approach can also be applied to descriptions of all the commensurate structures. In addition to the ternary M 2As2O7 phases, the quaternary phase (Ni,Co)2As2O7 was prepared and structurally characterized. In contrast to the previously published crystal structure of the mineral petewilliamsite, which has the same idealized formula and has been described as a 15-fold superstructure of the thortveitite-type basic structure in space group C2, synthetic (Ni,Co)2As2O7 can be considered as a solid solution adopting the α-Ni2As2O7 structure type. Differences of the two structure models for (Ni,Co)2As2O7 are discussed.

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