Phase transitions in ferroelectric 4-aminopyridinium tetrachloroantimonate(III) – revisited

2018 ◽  
Vol 74 (2) ◽  
pp. 217-225 ◽  
Author(s):  
Anna Gągor
Keyword(s):  
Crystal Structure ◽  
Ferroelectric Phase ◽  
Phase Iii ◽  
Polar Phase ◽  
X Ray Diffraction ◽  
Modulated Phases ◽  
Intermediate Phases ◽  
Modulated Phase ◽  
Lock In ◽  
Modulation Vector

New X-ray diffraction studies on the crystal structure of ferroelectric [4-NH2C5H4NH][SbCl4] indicate that in the broad temperature range from 240 to 304 K covering the three intermediate phases, the crystal structure is modulated. Phase II is incommensurately modulated with modulation vectorq= βb*, β varying from 0.60 to 0.66 and monoclinicC2/c(0β0)s0 superspace group. Ferroelectric phase III is commensurate withq= 2\over 3b*andCc(0β0)0 symmetry. Polar phase IV is incommensurately modulated with β varying from 0.66 to 0.70 andCc(0β0)0 superspace group. In all phases only first-order satellites are observed along theb*direction. Two types of periodic deformation are present in the structure of modulated phases. The 4-aminopyridinium cations are subjected to occupation modulation whereas [SbCl4]−nchains are displacively modulated. The paraelectric–ferroelectric phase transition is an example of the incommensurate–commensurate transition of the lock-in type. A new mechanism for this transformation is proposed.

Structures and phase transitions in a new ferroelectric – pyridinium chlorochromate – studied by X-ray diffraction, DSC and dielectric methods

2012 ◽  
Vol 68 (2) ◽  
pp. 128-136 ◽  
Author(s):  
Hanna Małuszyńska ◽  
Piotr Czarnecki ◽  
Anna Czarnecka ◽  
Zdzisław Pająk
Keyword(s):  
Phase Transitions ◽  
Pyridinium Salt ◽  
Diffraction Method ◽  
Phase Iii ◽  
Pyridinium Chlorochromate ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Intermediate Phases ◽  
Ferroelectric Hysteresis

Pyridinium chlorochromate, [C5H5NH]+[ClCrO3]− (hereafter referred to as PyClCrO3), was studied by X-ray diffraction, differential scanning calorimetry (DSC) and dielectric methods. Studies reveal three reversible phase transitions at 346, 316 and 170 K with the following phase sequence: R\bar 3m (I) → R3m (II) → Cm (III) → Cc (IV), c′ = 2c. PyClCrO3 is the first pyridinium salt in which all four phases have been successfully characterized by a single-crystal X-ray diffraction method. Structural results together with dielectric and calorimetric studies allow the classification of the two intermediate phases (II) and (III) as ferroelectric with the Curie point at 346 K, and the lowest phase (IV) as most probably ferroelectric. The ferroelectric hysteresis loop was observed only in phase (III). The high ionic conductivity hindered its observation in phase (II).

scholarly journals Structural Study of Ferroelectric Phase Transition of Sn-doped SrTiO3

2014 ◽  
Vol 70 (a1) ◽  
pp. C61-C61 ◽  
Author(s):  
Hirofumi Kasatani ◽  
Shoichiro Suzuki ◽  
Akira Ando ◽  
Eisuke Magome ◽  
Chikako Moriyoshi ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Local Structure ◽  
Ferroelectric Phase Transition ◽  
Nearest Neighbor ◽  
Ferroelectric Phase ◽  
Rietveld Analysis ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray

Recently, ferroelectricity was discovered in Sn-doped SrTiO3 (abbreviated by SSTO), in which Sr-atom was substituted by a few percent Sn-atom[1]. The ferroelctricity of SSTO was confirmed by means of the appearance of the dielectric anomaly, that reached several thousands and the clear D-E hysteresis loop in low temperature phase. In order to clarify the mechanism of ferroelectric phase transition of SSTO from the viewpoint of the crystal structure, we investigated the average crystal structure and the local structure around the substitutional Sn-atom of SSTO10 (10% Sn concentration, ferroelectric phase transition temperature 180K) by means of synchrotron-radiation powder X-ray diffraction and transmission XAFS spectrum of Sn:K-edge, respectively. From the results of MEM/Rietveld analysis of powder X-ray diffraction data, it was obtained that crystal structure of paraelectric phase of SSTO10 was cubic perovskite structure with the disorder state of Sn-atom. In ferroelectric phase, the crystal system was tetragonal, which was similar in structure to tetragonal ferroelectric structure of BaTiO3, and Sn-atom was order state. XAFS study revealed that the valence of Sn-ion was +2 charge and the local structure of Sn-atom was seemed as being the self-insistent state of SnO crystal structure. However, strangely, the coordination number of the nearest neighbor atom, that is O-atom, was 2 instead of 4. This is a mystery result and we have been analyzing. We have considered that the ferroelectricity of SSTO is induced by the distortion around the subsitituional Sn-atom. At the meeting, we are planning to discuss the precise crystal structure and the mechanism of the ferroelectric phase transition of SSTO.

Formation of U-type hexaferrites

2004 ◽  
Vol 19 (8) ◽  
pp. 2462-2470 ◽  
Author(s):  
Darja Lisjak ◽  
Darko Makovec ◽  
Miha Drofenik
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Stacking Faults ◽  
High Energy ◽  
Structural Defects ◽  
X Ray Diffraction ◽  
X Ray ◽  
Calcination Temperatures ◽  
Intermediate Phases ◽  
Transmission Electron

The formation of U-type hexaferrites with the composition Ba4B2Fe36O60 (B = Co, Ni, Zn) was studied. Samples were characterized by means of x-ray diffraction, electron microscopy (with energy-dispersive spectroscopy), and thermogravimetric and thermomagnetic analyses. U-hexaferrites are formed from the intermediate phases M-hexaferrite (BaFe12O19) and Y-hexaferrite (Ba2B2Fe12O22), which at the same time represent units in the U-hexaferrites’ crystal structure. The preparation of monophase U-hexaferrites was made possible by combining high-energy milling or chemical coprecipitation with a calcination at 1250–1300 °C. Structural defects, such as stacking faults, were observed in monophase samples with a high-resolution transmission electron microscope. The observed defects can be regarded as seeds for the formation of other hexaferrite phases after prolonged calcination times or higher calcination temperatures.

scholarly journals The crystal structure of Rb2Ti2O5

2017 ◽  
Vol 73 (6) ◽  
pp. 1142-1150 ◽  
Author(s):  
Rémi Federicci ◽  
Benoit Baptiste ◽  
Fabio Finocchi ◽  
Florin Popa ◽  
Luc Brohan ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Structural Transition ◽  
Ferroelectric Phase ◽  
Density Functional Theory Calculations ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Transmission Electron ◽  
The Stability

Recent results have demonstrated an exceptionally high permittivity in the range 200–330 K in crystalline titanium oxide Rb2Ti2O5. In this article, the possibility of a structural transition giving rise to ferroelectricity is carefully inspected. In particular, X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy are performed. The crystal structure is shown to remain invariant and centrosymmetric at all temperatures between 90 K and 450 K. The stability of the C2/m structure is confirmed by density functional theory calculations. These important findings allow the existence of a conventional ferroelectric phase transition to be ruled out as a possible mechanism for the colossal permittivity and polarization observed in this material.

scholarly journals Structure of methane and ethane at high pressure

2014 ◽  
Vol 70 (a1) ◽  
pp. C757-C757 ◽  
Author(s):  
Alexander Goncharov ◽  
Elissaios Stavrou ◽  
Sergey Lobanov ◽  
Artem Oganov ◽  
Valery Roisen ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Relative Stability ◽  
Room Temperature ◽  
High Pressures ◽  
Equations Of State ◽  
Theoretical Calculations ◽  
Chemical Reactivity ◽  
Phase Iii ◽  
X Ray Diffraction ◽  
Theoretical Predictions

Methane is one of the most abundant hydrocarbon molecules in the universe and is expected to be a significant part of the icy giant planets (Uranus and Neptune) and their satellites. Ethane is one of the most predictable products of chemical reactivity of methane at extreme pressures and temperatures. In spite of numerous experimental and theoretical studies, the structure and relative stability of these materials even at room temperature remains controversial. We have performed a combined experimental and theoretical study of both methane and ethane up at high pressures up to 120 GPa at 300 K using x-ray diffraction and Raman spectroscopy and the ab-initio evolutionary algorithm, respectively. In the case of methane we have successfully solved the structure of phase B by determining the space group and the positional parameters of carbon atoms, and by completing these results for the hydrogen positions using the theoretical calculations. The general structural behavior under pressure and the relation between phase B and phases A and pre-B will be also discussed. For ethane we have determined the crystallization point, for room temperature, at 1.7 GPa and also the low pressure crystal structure (Phase A). This crystal structure is orientationally disordered (plastic phase) and deviates from the known crystal structures for ethane at low temperatures. Moreover, a pressure induced phase transition has been indentified, for the first time, at 18 GPa to a monoclinic phase III, the structure of which is solved based on a good agreement of the experimental results and theoretical predictions. We have determined the equations of state of methane and ethane, which provides a solid basis for the discussion of their relative stability at high pressures.

Crystal Structure of Pyridinium Periodate

1998 ◽  
Vol 53 (11) ◽  
pp. 1323-1325 ◽  
Author(s):  
Grzegorz Dutkiewicz ◽  
Zdzisław Pająk
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Ferroelectric Phase ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Pyridinium Cations

The crystal structure of the room-temperature ferroelectric phase of pyridinium periodate [C6H5NH]+[IO4]- has been determined by X-ray diffraction as orthorhombic, space group Cmc2i with a = 8.347(2), b = 7.270(2), c = 12.732(3) Å and Z = 4. It was refined to R1 =0.0281 wR2 = 0.0762 for 389 absorption-corrected reflections. The structure comprises isolated IO4 tetrahedra linked together by disordered pyridinium cations involved in a network of bifurcated hydrogen bonds. The average I-O distance is found to be 1.75(1) Å.

Crystal Structure of Trimethylammonium Tetrafluoroborate in Three Solid Phases

2000 ◽  
Vol 55 (9-10) ◽  
pp. 765-768 ◽  
Author(s):  
Hiroyuki Ishida ◽  
Setsuo Kashino ◽  
Ryuichi Ikeda
Keyword(s):  
Crystal Structure ◽  
Phase Iii ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cscl Type ◽  
Lattice Space ◽  
Plastic Phase ◽  
Solid Phases ◽  
Phase Phase

Abstract The crystal structure of (CH3)3 NHBF 4 was studied in three solid phases by X-ray diffraction techniques. The structures of the ionic plastic phase (Phase I) stable above 453 K and Phase II between 384 and 453 K are CsCl-type cubic (a = 5.772(4) Å) and tetragonal (a = 9.815(5) and c = 6.895(5) Å), respectively. The room temperature phase (Phase III) forms a monoclinic lattice (space group P21/m, a = 5.7017(8), b = 8.5724(9), c = 7.444(1) Å, and ß = 102.76(1)°). BF4− ions in this phase were shown to be disordered in four orientations.

Modulated corrugations in the crystal structure of the superconductor CaAlSi

2006 ◽  
Vol 62 (5) ◽  
pp. 710-718 ◽  
Author(s):  
Karine M. Sparta ◽  
Ralf Müller ◽  
Michael Merz ◽  
Georg Roth ◽  
Peter Adelmann ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Thermal History ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Modulated Structure ◽  
X Ray ◽  
Modulated Phases ◽  
Modulated Structures ◽  
History Of

We report the crystal structure analyses of CaAlSi from single-crystal and powder X-ray diffraction and the existence of two commensurately modulated phases, a sixfold and a fivefold modulated structure. This polymorphism seems to be correlated to the thermal history of the sample. We describe both modulated structures using a three-dimensional and a (3 + 1)-dimensional formalism.

Electron Microscopy/Diffraction Study of the Ternary Mn-Er-S System

1990 ◽  
Vol 48 (1) ◽  
pp. 76-77
Author(s):  
A. R. Landa Canovas ◽  
L.C. Otero Diaz ◽  
T. White ◽  
B.G. Hyde
Keyword(s):  
Electron Microscopy ◽  
Gas Flow ◽  
Graphite Crucible ◽  
Nominal Composition ◽  
X Ray Diffraction ◽  
Alumina Crucible ◽  
X Ray ◽  
Intermediate Phases ◽  
Twin Band ◽  
Ar Gas

X-Ray diffraction revealed two intermediate phases in the system MnS+Er2S3,:MnEr2S4= MnS.Er2S3, and MnEr4S7= MnS.2Er2S3. Their structures may be described as NaCl type, chemically twinned at the unit cell level, and isostructural with CaTi2O4, and Y5S7 respectively; i.e. {l13} NaCl twin band widths are (4,4) and (4,3).The present study was to search for structurally-related (twinned B.) structures and or possible disorder, using the more sensitive and appropiate technigue of electron microscopy/diffraction.A sample with nominal composition MnEr2S4 was made by heating Mn3O4 and Er2O3 in a graphite crucible and a 5% H2S in Ar gas flow at 1500°C for 4 hours. A small amount of this material was thenannealed, in an alumina crucible, contained in sealed evacuated silica tube, for 24 days at 1100°C. Both samples were studied by X-ray powder diffraction, and in JEOL 2000 FX and 4000 EX microscopes.

Crystal structure of an inclusion complex between chiral monoaza-15-crown-5 and S(–)-1-phenyl-ethyl ammonium percholorate

2003 ◽  
Vol 218 (5) ◽  
Author(s):  
Süheyla Özbey ◽  
F. B. Kaynak ◽  
M. Toğrul ◽  
N. Demirel ◽  
H. Hoşgören
Keyword(s):  
Crystal Structure ◽  
Inclusion Complex ◽  
Single Crystal ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
New Type

AbstractA new type of inclusion complex, S(–)-1 phenyl ethyl ammonium percholorate complex of R-(–)-2-ethyl - N - benzyl - 4, 7, 10, 13 - tetraoxa -1- azacyclopentadecane, has been prepared and studied by NMR, IR and single crystal X-ray diffraction techniques. The compound crystallizes in space group

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