Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

1990 ◽  
Vol 48 (4) ◽  
pp. 172-173
Author(s):  
Naoki Yamamoto ◽  
Makoto Kikuchi ◽  
Tooru Atake ◽  
Akihiro Hamano ◽  
Yasutoshi Saito
Keyword(s):  
Phase Transition ◽  
Electron Microscope Study ◽  
Room Temperature ◽  
Hexagonal Lattice ◽  
Ferroelectric Materials ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Periodic Arrays ◽  
Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

Powder Diffraction Data of Polymorphic Phases of Dicesium Cadmium Tetraiodide Cs2CdI4

1986 ◽  
Vol 1 (2) ◽  
pp. 35-36 ◽  
Author(s):  
V. Touchard ◽  
M. Louër ◽  
D. Louër
Keyword(s):  
Phase Transition ◽  
Thermal Analysis ◽  
Room Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Powder Diffraction Data ◽  
X Ray Diffraction ◽  
Indexing Methods ◽  
X Ray ◽  
Two Phases

Introduction: Phase transition has been recently observed in Cs2CdI4 (Touchard, Louër, Auffrédic & Louër, 1986). Thermal analysis has shown that the transformation occurs at 122°C. By quenching, the high temperature phase (β) can be stabilized at room temperature. In the present work we report the X-ray diffraction powder data, at room temperature, for the two phases α- and β-Cs2CdI4. Both phases have been indexed automatically by using powder indexing methods.

scholarly journals Studies of Structure and Phase Transition in [C(NH2)3]HgBr3 and [C(NH2)3]HgI3 by Means of Halogen NQR, 1H NMR, and Single Crystal X-Ray Diffraction

2000 ◽  
Vol 55 (1-2) ◽  
pp. 230-236 ◽  
Author(s):  
Hiromitsu Terao ◽  
Masao Hashimoto ◽  
Shinichi Hashimoto ◽  
Yoshihiro Furukawa
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
H Nmr ◽  
Trigonal Bipyramidal ◽  
Second Order Phase Transition

(TThe crystal structure of [C(NH2)3]HgBr3 was determined at room temperature: monoclinic, space group C2/c, Z = 4, a = 775.0(2), b = 1564.6(2), c = 772.7(2) pm, β = 109.12(2)°. In the crystal, almost planar HgBr3- ions are connected via Hg ··· Br bonds, resulting in single chains of trigonal bipyramidal HgBr5 units which run along the c direction. [C(NH2)3]HgI3 was found to be isomorphous with the bromide at room temperature. The temperature dependence of the halogen NQR frequencies (77 < 77K < ca. 380) and the DTA measurements evidenced no phase transition for the bromide, but a second-order phase transition at (251 ± 1) K (Tc1) and a first-order one at (210 ± 1) K for the iodide. The transitions at Tc2are accompanied with strong supercooling and significant superheating. The room temperature phase (RTP) and the intermediate temperature phase (ITP) of the iodide are characterized by two 127I(m=1/2↔3/2) NQR lines which are assigned to the terminal and the bridging I atoms, respectively. There exist three lines in the lowest temperature phase (LTP), indicating that the resonance line of the bridging atom splits into two. The signal intensities of the 127I(m =1/2↔3/2) NQR lines in the LTP decrease with decreasing temperature resulting in no detection below ca. 100 K. The 127I(m=1/2↔3/2) NQR frequency vs. temperature curves are continuous at Tcl, but they are unusual in the LTP. The T1vs. Tcurves of 1H NMR for the bromide and iodide are explainable by the reorientational motions of the cations about their pseudo three-fold axes. The estimated activation energies of the motions are 35.0 kJ/mol for the bromide, and 24.1, 30.1, and 23.0 kJ/mol for the RTP, FTP, and LTP of the iodide, respectively

scholarly journals High-temperature phase transition of SrRuO3and SrHfO5: X-ray diffraction and PAC spectroscopy

1996 ◽  
Vol 52 (a1) ◽  
pp. C364-C364
Author(s):  
J. A. Guevara ◽  
S. L. Cuffini ◽  
Y. P. Mascarenhas ◽  
P. de la Presa ◽  
A. Ayala ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Pac Spectroscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Phase Transition

Rotational Polymorphism of Methyl-Substituted Ammonium Perchlorates

1965 ◽  
Vol 9 ◽  
pp. 170-189 ◽  
Author(s):  
M. Stammler ◽  
R. Bruenner ◽  
W. Schmidt ◽  
D. Orcutt
Keyword(s):  
Phase Transition ◽  
Ammonium Perchlorate ◽  
Room Temperature ◽  
Decomposition Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Analysis Techniques ◽  
Cell Dimensions ◽  
Thermal Analysis Techniques ◽  
Space Requirements

AbstractThe thermal transformations which take place in solid methyl-substituted ammonium perchlorates have been studied using high-temperature X-ray diffraction and differential thermal analysis techniques. In the temperature range from 20°C to their decomposition temperature (above 300°C), ammonium perchlorate and tetramethyl ammonium perchlorate undergo only one enantiomorphic phase transition, namely at 240 and 340°C (with decomposition), respectively. This I—II transition is ascribed to the beginning of the free rotation of the ClO4− ions. The rotation of the cations, however, begins below room temperature. If the symmetry of the cation is lowered by having both methyl groups and hydrogens arranged around the nitrogen (as in monomethyl, dimethyl, and trimethyl ammonium perchlorates), there is an additional enantiomorphic phase transition. This I—II transformation is ascribed to the rotation of the cations which have, in the partially substituted ions, two sets of non-equivalent symmetry axes (different moments of inertia). The temperatures of transformation are discussed in terms of the space requirements for rotation. Symmetries and cell dimensions of some modifications were determined.

The structures and phase transitions in 4-aminopyridinium tetraaquabis(sulfato)iron(III), (C5H7N2)[FeIII(H2O)4(SO4)2]

2019 ◽  
Vol 75 (6) ◽  
pp. 1144-1151
Author(s):  
Tamara J. Bednarchuk ◽  
Wolfgang Hornfeck ◽  
Vasyl Kinzhybalo ◽  
Zhengyang Zhou ◽  
Michal Dušek ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Single Crystal ◽  
Room Temperature ◽  
Variable Temperature ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Hybrid Compound ◽  
Space Group ◽  
X Ray

The organic–inorganic hybrid compound 4-aminopyridinium tetraaquabis(sulfato)iron(III), (C5H7N2)[FeIII(H2O)4(SO4)2] (4apFeS), was obtained by slow evaporation of the solvent at room temperature and characterized by single-crystal X-ray diffraction in the temperature range from 290 to 80 K. Differential scanning calorimetry revealed that the title compound undergoes a sequence of three reversible phase transitions, which has been verified by variable-temperature X-ray diffraction analysis during cooling–heating cycles over the temperature ranges 290–100–290 K. In the room-temperature phase (I), space group C2/c, oxygen atoms from the closest Fe-atom environment (octahedral) were disordered over two equivalent positions around a twofold axis. Two intermediate phases (II), (III) were solved and refined as incommensurately modulated structures, employing the superspace formalism applied to single-crystal X-ray diffraction data. Both structures can be described in the (3+1)-dimensional monoclinic X2/c(α,0,γ)0s superspace group (where X is ½, ½, 0, ½) with modulation wavevectors q = (0.2943, 0, 0.5640) and q = (0.3366, 0, 0.5544) for phases (II) and (III), respectively. The completely ordered low-temperature phase (IV) was refined with the twinning model in the triclinic P{\overline 1} space group, revealing the existence of two domains. The dynamics of the disordered anionic substructure in the 4apFeS crystal seems to play an essential role in the phase transition mechanisms. The discrete organic moieties were found to be fully ordered even at room temperature.

Differences and similarities among hypoxanthinium nitrate hydrate structures

2019 ◽  
Vol 75 (8) ◽  
pp. 1036-1044 ◽  
Author(s):  
Małgorzata Katarzyna Cabaj ◽  
Roman Gajda ◽  
Anna Hoser ◽  
Anna Makal ◽  
Paulina Maria Dominiak
Keyword(s):  
Room Temperature ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Acta Cryst ◽  
X Ray ◽  
Nitrate Hydrate ◽  
Different Temperatures ◽  
Lower Temperature ◽  
Low Temperature Phase ◽  
Nitrate Anions

Crystals of hypoxanthinium (6-oxo-1H,7H-purin-9-ium) nitrate hydrates were investigated by means of X-ray diffraction at different temperatures. The data for hypoxanthinium nitrate monohydrate (C5H5N4O+·NO3 −·H2O, Hx1) were collected at 20, 105 and 285 K. The room-temperature phase was reported previously [Schmalle et al. (1990). Acta Cryst. C46, 340–342] and the low-temperature phase has not been investigated yet. The structure underwent a phase transition, which resulted in a change of space group from Pmnb to P21/n at lower temperature and subsequently in nonmerohedral twinning. The structure of hypoxanthinium dinitrate trihydrate (H3O+·C5H5N4O+·2NO3 −·2H2O, Hx2) was determined at 20 and 100 K, and also has not been reported previously. The Hx2 structure consists of two types of layers: the `hypoxanthinium nitrate monohydrate' layers (HX) observed in Hx1 and layers of Zundel complex H3O+·H2O interacting with nitrate anions (OX). The crystal can be considered as a solid solution of two salts, i.e. hypoxanthinium nitrate monohydrate, C5H5N4O+·NO3 −·H2O, and oxonium nitrate monohydrate, H3O+(H2O)·NO3 −.

On the tetragonality of the room-temperature ferroelectric phase of barium titanate, BaTiO3

2009 ◽  
Vol 42 (3) ◽  
pp. 480-484 ◽  
Author(s):  
Dean S. Keeble ◽  
Pamela A. Thomas
Keyword(s):  
Barium Titanate ◽  
Diffraction Pattern ◽  
Room Temperature ◽  
Ferroelectric Material ◽  
Tetragonal Symmetry ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Group Assignment ◽  
Growth Method

The room-temperature phase of the important ferroelectric material barium titanate, BaTiO3, was re-investigated by single-crystal X-ray diffraction on a sample grown by the top-seeded solution growth method, with the intention of demonstrating once again that the structure has tetragonal symmetry consistent with the space-group assignmentP4mmand thus resolving recent controversy in the scientific community and literature [Yoshimura, Kojima, Tokunaga, Tozaki & Koganezawa (2006).Phys. Lett. A,353, 250–254; Yoshimura, Morioka, Kojima, Tokunaga, Koganezawa & Tozaki (2007).Phys. Lett. A,367, 394–401]. To this end, the X-ray diffraction pattern of a small (341 µm3) sample of top-seeded solution-grown BaTiO3was measured using an Oxford Diffraction Gemini CCD diffractometer employing Mo Kα radiation and an extended 120 mm sample-to-detector distance. More than 104individual diffraction maxima observed out to a maximum resolution of 0.4 Å were indexed on two tetragonal lattices. These were identical to within the standard deviations on the lattice parameters and were related to each other by a single rotation of 119.7° about the [11\overline1] direction of the first tetragonal lattice (the major twin component), although the actual twinning operation that explains the observed diffraction pattern both qualitatively and quantitatively is shown to be conventional 90° twinning by them[101] operation. Importantly, it is not necessary to invoke either monoclinic symmetry or a coexistence of tetragonal and monoclinic phases to explain the observed diffraction data.

Structure and phase transition of the Se-rich variety of antimonpearceite, [(Ag,Cu)6(Sb,As)2(S,Se)7][Ag9Cu(S,Se)2Se2]

2006 ◽  
Vol 62 (5) ◽  
pp. 768-774 ◽  
Author(s):  
Michel Evain ◽  
Luca Bindi ◽  
Silvio Menchetti
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Atomic Displacement ◽  
X Ray Diffraction ◽  
X Ray ◽  
Dimensional Diffusion ◽  
Ionic Conducting ◽  
Local Arrangement ◽  
Diffusion Paths ◽  
Linear Coordination

The crystal structure of a Se-rich antimonpearceite has been solved and refined by means of X-ray diffraction data collected at temperatures above (room temperature) and below (120 K) an ionic conductivity-induced phase transition. Both structure arrangements consist of the stacking of [(Ag,Cu)6(Sb,As)2(S,Se)7]2− A (A′) and [Ag9Cu(S,Se)2Se2]2+ B (B′) module layers in which Sb forms isolated SbS3 pyramids typically occurring in sulfosalts; copper links two S atoms in a linear coordination, and silver occupies sites with coordination ranging from quasi-linear to almost tetrahedral. In the ionic-conducting form, at room temperature, the silver d 10 ions are found in the B (B′) module layer along two-dimensional diffusion paths and their electron densities described by means of a combination of a Gram–Charlier development of the atomic displacement factors and a split-atom model. The structure resembles that of pearceite, except for the presence of both specific (Se) and mixed (S, Se) sites. In the low-temperature `ordered' phase at 120 K the silver d 10 ions of the B (B′) module layer are located in well defined sites with mixed S—Se coordination ranging from quasi-linear to almost tetrahedral. The structure is then similar to that of 222-pearceite but with major differences, specifically its cell metric, symmetry and local arrangement in the B (B′) module layer.

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