High-pressure-induced structural changes in molecular crystals preserving the space group symmetry: anisotropic distortion/isosymmetric polymorphism

2003 ◽  
Vol 6 (4) ◽  
pp. 235-254 ◽  
Author(s):  
Elena V. Boldyreva
Keyword(s):  
High Pressure ◽  
Structural Changes ◽  
Molecular Crystals ◽  
Group Symmetry ◽  
Space Group Symmetry ◽  
Space Group

scholarly journals Optical properties of GaAs 2D Archimedean photonic lattice tiling with the p4g symmetry

2008 ◽  
Vol 40 (2) ◽  
pp. 167-173 ◽  
Author(s):  
Dj. Jovanovic ◽  
R. Gajic ◽  
K. Hingerl
Keyword(s):  
Optical Properties ◽  
Photonic Crystal ◽  
Photonic Crystals ◽  
Negative Refraction ◽  
Group Symmetry ◽  
Electromagnetic Propagation ◽  
Space Group Symmetry ◽  
Space Group ◽  
Left Handedness ◽  
Archimedean Lattice

In this paper we present our investigation of 2D Archimedean lattice photonic crystals with p4g space group symmetry. The structures are made of GaAs both as air holes and dielectric rods in air. In order to analyze the photonic crystal optical properties we performed calculations of the band structures, equi-frequency contours and electromagnetic propagation through the basic structures and waveguides. In addition, we investigated negative refraction and left-handedness in the p4g photonic crystal.

scholarly journals Symmetrical Analysis Phonon Modes of Crystal -Ag8SnSe6

2015 ◽  
Vol 16 (2) ◽  
pp. 257-260
Author(s):  
І.V. Semkiv ◽  
А.І. Kashuba ◽  
H.A. Ilchuk ◽  
M.V. Chekaylo
Keyword(s):  
Raman Spectra ◽  
Infrared Spectra ◽  
Room Temperature ◽  
Group Symmetry ◽  
Phonon Modes ◽  
Orthorhombic System ◽  
Space Group Symmetry ◽  
Space Group ◽  
Phonon Spectra

Symmetrical analysis of the phonon spectra of  lowtemperature b¢-phase of crystal Ag8SnSe6 carried out. At the room temperature argyrodite Ag8SnSe6 belong to orthorhombic system with space group symmetry Pmn21. Classification of the main phonon modes of crystal carried out. Clarified selection rules for Raman spectra and infrared spectra.

Electron Diffraction Study of α-AlMnSi Crystals Along Non-Crystallographic Zone Axes

1998 ◽  
Vol 12 (22) ◽  
pp. 2279-2303 ◽  
Author(s):  
G. L. Song ◽  
L. A. Bursill
Keyword(s):  
Electron Diffraction ◽  
Significant Proportion ◽  
Group Symmetry ◽  
Structural Basis ◽  
Quasicrystalline Phase ◽  
Thickness Variation ◽  
Crystal Thickness ◽  
Space Group Symmetry ◽  
Space Group ◽  
Diffraction Patterns

The structure of crystalline α-AlMnSi is examined by electron diffraction. Six distinct zone axes are examined, including both normal crystallographic and non-crystallographic zone axes, allowing the space group symmetry of α-AlMnSi to be studied. A method for indexing the non-crystallographic zone axis diffraction patterns, which involve reflections from several nearby crystallographic zone axes, is described and applied to electron diffraction patterns of the quasi-5-fold, 3-fold and 2-fold axes of the icosahedral building units of cubic α-AlMnSi. These are compared with electron diffraction patterns from the corresponding 5-fold, 3-fold and 2-fold axes of the quasicrystalline phase i-AlMnSi, from which we may make some conclusions concerning the occupancies of the icosahedral units in i-AlMnSi. Electron diffraction patterns characteristic of [Formula: see text] were obtained for thicker specimens. However, for thin specimens, as used for HRTEM imaging, the electron diffraction patterns were characteristic of [Formula: see text] space group symmetry. This unusual behaviour arises because the structural basis for the [Formula: see text] to [Formula: see text] phase transition is a weak effect, involving changes in occupancy of the icosahedral structural elements located at the corners (double-MacKay icosahedra) and body-centers (MacKay icosahedra) of the cubic unit cell. The effects of changing the occupancies of the outer shells of the MI and DMI structural units on the diffraction intensities of the weak reflections were examined. Thus, calculation of the dynamical diffraction amplitudes shows that in fact the weak reflections characteristic of [Formula: see text] only develop sufficient intensity if two conditions are satisfied: namely (1) the crystal thickness exceeds approx. 50 nm and (2) if a significant proportion of [Formula: see text] occupancies are included in the structural model. By fitting the observed thickness variation of the diffraction intensities we propose a new set of occupancies for α-AlMnSi, which is consistent with the electron, X-ray and neutron diffraction data.

The Space Group Symmetry of PSN, PST and PSNT Ferroelectric Relaxors in the Superparaelectric Phase

2004 ◽  
Vol 298 (1) ◽  
pp. 235-241 ◽  
Author(s):  
Adam Pietraszko ◽  
Bożena Hilczer ◽  
Claude Caranoni
Keyword(s):  
Group Symmetry ◽  
Space Group Symmetry ◽  
Space Group ◽  
Ferroelectric Relaxors

Space-group symmetry for the perovskite Ca0.3Sr0.7TiO3

2005 ◽  
Vol 17 (44) ◽  
pp. L459-L465 ◽  
Author(s):  
C J Howard ◽  
R L Withers ◽  
Z Zhang ◽  
K Osaka ◽  
K Kato ◽  
...  
Keyword(s):  
Group Symmetry ◽  
Space Group Symmetry ◽  
Space Group
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