Conformational transformation coupled with the order–disorder phase transition in 2-methyl-1,3-cyclohexanedione crystals

2000 ◽  
Vol 56 (5) ◽  
pp. 872-881 ◽  
Author(s):  
Andrzej Katrusiak
Keyword(s):  
Phase Transition ◽  
Chair Conformation ◽  
Continuous Phase ◽  
Conformational Transformation ◽  
X Ray Diffraction ◽  
Ring Conformation ◽  
X Ray ◽  
Disorder Phase Transition ◽  
Methylene Groups ◽  
Large Amplitude Vibrations

The half-chair conformation of the dynamically disordered molecular ring of 2-methyl-1,3-cyclohexanedione, C_7H_{10}O_2, transforms to a sofa below T_c = 244 K, when the crystal undergoes a continuous phase transition induced by the onset of halting large-amplitude vibrations of methylene groups C(4)H_2 and C(5)H_2. The temperature dependence of the crystal structure has been investigated by X-ray diffraction. The Ibam symmetry of the crystal reduces below T_c to space group Pccn. The mechanism of the phase transition and of the conversion of the ring conformation is discussed.

X-ray Diffraction Study of Order–Disorder Phase Transition in CuMPt6 (M=3d Elements) Alloys

2009 ◽  
Vol 78 (1) ◽  
pp. 014601 ◽  
Author(s):  
Ejaz Ahmed ◽  
Miwako Takahashi ◽  
Hiroshi Iwasaki ◽  
Ken-ichi Ohshima
Keyword(s):  
Phase Transition ◽  
Diffraction Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Disorder Phase Transition ◽  
3D Elements

scholarly journals Order–disorder phase transition of the subsurface cation vacancy reconstruction on Fe3O4(001)

2020 ◽  
Vol 22 (16) ◽  
pp. 8336-8343 ◽  
Author(s):  
Björn Arndt ◽  
Barbara A. J. Lechner ◽  
Alexander Bourgund ◽  
Elin Grånäs ◽  
Marcus Creutzburg ◽  
...  
Keyword(s):  
Phase Transition ◽  
Scanning Tunneling Microscopy ◽  
Surface Defect ◽  
Cation Vacancy ◽  
Scanning Tunneling ◽  
X Ray Diffraction ◽  
Tunneling Microscopy ◽  
X Ray ◽  
Disorder Phase Transition

Magnetite surface defect dynamics followed by fast scanning tunneling microscopy and surface X-ray diffraction.

The phase transitions and crystal structures of Ba3 RM 2O7.5 complex oxides (R = rare-earth elements, M = Al, Ga)

1999 ◽  
Vol 55 (5) ◽  
pp. 828-839 ◽  
Author(s):  
A. M. Abakumov ◽  
R. V. Shpanchenko ◽  
O. I. Lebedev ◽  
G. Van Tendeloo ◽  
S. Amelinckx ◽  
...  
Keyword(s):  
Phase Transition ◽  
Rare Earth ◽  
High Temperature ◽  
Rare Earth Elements ◽  
Complex Oxides ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Disorder Phase Transition

The structures of α-Ba3 RAl2O7.5 and β-Ba3 RM 2O7.5 complex oxides (R = rare-earth elements, M = Al, Ga) have been studied by a combination of X-ray diffraction, electron diffraction (ED) and high-resolution electron microscopy (HREM). The α and β forms have cell parameters related to the perovskite subcell: a = 2a per, b = a per(2)1/2, c = 3a per(2)1/2, however, the α form has an orthorhombic unit cell whereas the β form adopts monoclinic symmetry. The crystal structure of monoclinic Ba3ErGa2O7.5 was refined from X-ray powder data (space group P2/c, a = 7.93617 (9), b = 5.96390 (7), c = 18.4416 (2) Å, β = 91.325 (1)°, R I = 0.023, R P = 0.053), the structure of the α form (space group Cmc21) was deduced from ED and HREM data. The important feature of the α and β structures is the presence of slabs containing strings of vertex-sharing tetrahedral Al2O7 pairs. Two almost equivalent oxygen positions within the strings can be occupied either in an ordered manner leading to the low-temperature β phase or randomly resulting in the high-temperature α structure. The critical temperature of this order–disorder phase transition was determined by high-temperature X-ray diffraction and by differential thermal analysis (DTA). In situ ED and HREM observations of the second-order phase transition confirmed the symmetry changes and revealed numerous defects (twins and antiphase boundaries) formed during the phase transformation.

NQR View of Solid Phases of NOCl

1998 ◽  
Vol 53 (6-7) ◽  
pp. 537-541 ◽  
Author(s):  
J. Pirnat ◽  
Z. Trontelj ◽  
H. Borrmann
Keyword(s):  
Phase Transition ◽  
Temperature Phase ◽  
Measured Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Disorder Phase Transition ◽  
Upper Limit ◽  
Temperature Phase Transition ◽  
Solid Phases ◽  
Low Temperature Phase

Abstract Chlorine NQR studies of solid nitrosyl chloride NOC1 between 110 and 212 K are reported. In the temperature dependence an order-disorder phase transition near 145 K, found by X-ray diffraction, is confirmed. Unusual hysteretic NQR signal behaviour indirectly proves also the low temperature phase transition below 100 K. In the measured temperature region fast relaxing mechanisms are present. The upper limit of the expected 14N NQR frequency is estimated using the Townes-Dailey approach.

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.

Crystal structure determination of the conformation of two bicyclo[3.3.1]nonan-ones

1985 ◽  
Vol 63 (6) ◽  
pp. 1166-1169 ◽  
Author(s):  
John F. Richardson ◽  
Ted S. Sorensen
Keyword(s):  
Crystal Structure ◽  
Direct Methods ◽  
Chair Conformation ◽  
Molecular Structures ◽  
Boat Conformation ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Final Agreement

The molecular structures of exo-7-methylbicyclo[3.3.1]nonan-3-one, 3, and the endo-7-methyl isomer, 4, have been determined using X-ray-diffraction techniques. Compound 3 crystallizes in the space group [Formula: see text] with a = 15.115(1), c = 7.677(2) Å, and Z = 8 while 4 crystallizes in the space group P21 with a = 6.446(1), b = 7.831(1), c = 8.414(2) Å, β = 94.42(2)°, and Z = 2. The structures were solved by direct methods and refined to final agreement factors of R = 0.041 and R = 0.034 for 3 and 4 respectively. Compound 3 exists in a chair–chair conformation and there is no significant flattening of the chair rings. However, in 4, the non-ketone ring is forced into a boat conformation. These results are significant in interpreting what conformations may be present in the related sp2-hybridized carbocations.

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