Propagation of light in Rb2ZnCl4-type crystals with incommensurate modulation

1986 ◽  
Vol 36 (10) ◽  
pp. 1192-1202 ◽  
Author(s):  
J. Fousek ◽  
J. Kroupa
Keyword(s):  
Propagation Of Light ◽  
Incommensurate Modulation

Incommensurate modulated phases of the NbxTa1-xTe4 charge density wave system

1992 ◽  
Vol 50 (1) ◽  
pp. 58-59
Author(s):  
S. Ritchie ◽  
J. C. Bennett ◽  
A. Prodan ◽  
F.W. Boswell ◽  
J.M. Corbett
Keyword(s):  
Charge Density ◽  
Charge Density Wave ◽  
Direct Evidence ◽  
Density Wave ◽  
Wave System ◽  
Modulated Phases ◽  
Metal Atoms ◽  
Incommensurate Modulation ◽  
End Members ◽  
Modulation Wave Vector

A continuous sequence of compounds having composition NbxTa1-xTe4; 0 ≤ x ≤ 1 have been studied by electron diffraction and microscopy. Previous studies have shown that the end members of the series, TaTε4 and NbTε4 possess a quasi-one-dimensional character and exhibit charge density wave (CDW) distortions. In these compounds, the subcell structure is tetragonal with axes (a × a × c) and consists of the metal atoms (Nb or Ta) centered within an extended antiprismatic cage of Te atoms. At room temperature, TaTε4 has a commensurate modulation structure with a 2a × 2a × 3c unit cell. In NbTε4, an incommensurate modulation with × ∼ 16c axes is observed. Preliminary studies of the mixed compounds NbxTα1-xTε4 showed a discontinuous jump of the modulation wave vector commensurate to incommensurate when the Nb dopant concentration x, exceeded x ≃ 0.3, In this paper, the nature of the compositional dependence of is studied in greater detail and evidence is presented for a stepwise variation of . This constitutes the first direct evidence for a Devil's staircase in CDW materials.

scholarly journals The Optical Properties of Leaf Structural Elements and Their Contribution to Photosynthetic Performance and Photoprotection

Plants ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1455
Author(s):  
George Karabourniotis ◽  
Georgios Liakopoulos ◽  
Panagiota Bresta ◽  
Dimosthenis Nikolopoulos
Keyword(s):  
Glandular Trichomes ◽  
Spectral Band ◽  
Co2 Assimilation ◽  
Photosynthetic Performance ◽  
Structural Elements ◽  
Internal Layers ◽  
Water Losses ◽  
Light Gradient ◽  
Propagation Of Light ◽  
Light Capture

Leaves have evolved to effectively harvest light, and, in parallel, to balance photosynthetic CO2 assimilation with water losses. At times, leaves must operate under light limiting conditions while at other instances (temporally distant or even within seconds), the same leaves must modulate light capture to avoid photoinhibition and achieve a uniform internal light gradient. The light-harvesting capacity and the photosynthetic performance of a given leaf are both determined by the organization and the properties of its structural elements, with some of these having evolved as adaptations to stressful environments. In this respect, the present review focuses on the optical roles of particular leaf structural elements (the light capture module) while integrating their involvement in other important functional modules. Superficial leaf tissues (epidermis including cuticle) and structures (epidermal appendages such as trichomes) play a crucial role against light interception. The epidermis, together with the cuticle, behaves as a reflector, as a selective UV filter and, in some cases, each epidermal cell acts as a lens focusing light to the interior. Non glandular trichomes reflect a considerable part of the solar radiation and absorb mainly in the UV spectral band. Mesophyll photosynthetic tissues and biominerals are involved in the efficient propagation of light within the mesophyll. Bundle sheath extensions and sclereids transfer light to internal layers of the mesophyll, particularly important in thick and compact leaves or in leaves with a flutter habit. All of the aforementioned structural elements have been typically optimized during evolution for multiple functions, thus offering adaptive advantages in challenging environments. Hence, each particular leaf design incorporates suitable optical traits advantageously and cost-effectively with the other fundamental functions of the leaf.

Crystallographic Features of Electronic States in the Highly-Correlated Electronic System Sr1-xSmxMnO3 around x = 0.50

2016 ◽  
Vol 879 ◽  
pp. 2158-2163 ◽  
Author(s):  
Misato Yamagata ◽  
Yasuhide Inoue ◽  
Yasumasa Koyama
Keyword(s):  
Electronic States ◽  
Electronic System ◽  
Electron System ◽  
Correlated Electron ◽  
Antiferromagnetic Ordering ◽  
Incommensurate Modulation ◽  
Charge Modulations ◽  
Highly Correlated ◽  
Correlated Electron System ◽  
Coexistence State

The highly-correlated electron system Sr1-xSmxMnO3 (SSMO) with the simple-perovskite structure has been found to exhibit fascinating electronic states accompanying antiferromagnetic and ferromagnetic orderings. It was, in particular, reported that the electronic state for 0.46 ≤ x ≤ 0.54 was characterized by the coexistence state consisting of the A-type antiferromagnetic and ferromagnetic states. However, the features of the coexistence state in this Sm-content range have not been understood yet. We have thus investigated the crystallographic features of prepared SSMO samples with 0.46 ≤ x ≤ 0.55, mainly by transmission electron microscopy. As a result, all prepared SSMO samples were first confirmed to have the orthorhombic-Pnma structure at 300 K. When the temperature was lowered from 300 K, in the case of x=0.47, the disordered-Pnma state was found to be transformed into an orbital-modulated (OM) state accompanying an incommensurate modulation. The notable feature of the OM state is that the state becomes unstable with increasing Sm contents at 100 K. In other words, the OM state was never changed into the CE-type state with the orbital and charge modulations. In addition, no orbital-ordered state for the A-type antiferromagnetic ordering was also found for 0.46 ≤ x ≤ 0.55.

scholarly journals Incommensurately Modulated Crystal Structure and Photoluminescence Properties of Eu2O3- and P2O5-Doped Ca2SiO4 Phosphor

Materials ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 58
Author(s):  
Hiromi Nakano ◽  
Shota Ando ◽  
Konatsu Kamimoto ◽  
Yuya Hiramatsu ◽  
Yuichi Michiue ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Light Emission ◽  
Red Light ◽  
Basic Unit ◽  
Β Phase ◽  
Stacking Order ◽  
Cell Dimensions ◽  
Incommensurate Modulation ◽  
Unit Cell Dimensions ◽  
Identical Chemical Composition

We prepared four types of Eu2O3- and P2O5-doped Ca2SiO4 phosphors with different phase compositions but identical chemical composition, the chemical formula of which was (Ca1.950Eu3+0.013☐0.037)(Si0.940P0.060)O4 (☐ denotes vacancies in Ca sites). One of the phosphors was composed exclusively of the incommensurate (IC) phase with superspace group Pnma(0β0)00s and basic unit-cell dimensions of a = 0.68004(2) nm, b = 0.54481(2) nm, and c = 0.93956(3) nm (Z = 4). The crystal structure was made up of four types of β-Ca2SiO4-related layers with an interlayer. The incommensurate modulation with wavelength of 4.110 × b was induced by the long-range stacking order of these layers. When increasing the relative amount of the IC-phase with respect to the coexisting β-phase, the red light emission intensity, under excitation at 394 nm, steadily decreased to reach the minimum, at which the specimen was composed exclusively of the IC-phase. The coordination environments of Eu3+ ion in the crystal structures of β- and IC-phases might be closely related to the photoluminescence intensities of the phosphors.

Modeling the propagation of light in photonic crystal fibers

2004 ◽  
Vol 189 (1-2) ◽  
pp. 100-106 ◽  
Author(s):  
J. Arriaga ◽  
J.C. Knight ◽  
P.St.J. Russell
Keyword(s):  
Photonic Crystal ◽  
Photonic Crystal Fibers ◽  
Propagation Of Light ◽  
Crystal Fibers

Incommensurate modulation of calcium barium niobate (CBN28 and Ce:CBN28)

2012 ◽  
Vol 68 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Heribert A. Graetsch ◽  
Chandra Shekhar Pandey ◽  
Jürgen Schreuer ◽  
Manfred Burianek ◽  
Manfred Mühlberg
Keyword(s):  
Crystal Structures ◽  
Tungsten Bronze ◽  
Atomic Displacement ◽  
Type Structure ◽  
Formula Unit ◽  
Tetragonal Tungsten Bronze ◽  
First Order ◽  
Oxygen Coordination ◽  
Incommensurate Modulation ◽  
Atomic Displacement Parameters

The incommensurately modulated crystal structures of Ca0.28Ba0.72Nb2O6 (CBN28) and Ce0.02Ca0.25Ba0.72Nb2O6 (Ce:CBN28) were refined in the supercentred setting X4bm(AA0,−AA0) of the 3 + 2-dimensional superspace group P4bm(aa½,−aa½). Both compounds are isostructural with a tetragonal tungsten bronze-type structure. The modulation of CBN28 consists of a wavy distribution of Ba and Ca atoms as well as vacancies on the incompletely occupied Me2 site with 15-fold oxygen coordination. The occupational modulation is coupled with a modulation of the atomic displacement parameters and a very weak modulation of the positional parameters of Me2. The surrounding O atoms show strong displacive modulations with amplitudes up to ca 0.2 Å owing to the cooperative tilting of the rigid NbO6 octahedra. The Me1 site with 12-fold coordination and Nb atoms are hardly affected by the modulations. Only first-order satellites were observed and the modulations are described by first-order harmonics. In Ce:CBN28 cerium appears to be located on both the Me2 and Me1 sites. Wavevectors and structural modulations are only weakly modified upon substitutional incorporation of 0.02 cerium per formula unit of calcium.

scholarly journals VI. Experiments on the production and propagation of light from the phosphorus in vacuo , made before the Royal Society by Mr. Fra. Hauksbee

1705 ◽  
Vol 24 (296) ◽  
pp. 1865-1866
Keyword(s):  
Royal Society ◽  
Propagation Of Light ◽  
Dark Room

Experiment I. In pursuance to the Commands of his Honourable Society, Having a dark Room provided, the first Experiment was by drawing some Lines on a piece of blue Paper with the Phosphorus , which became immediately Luminous in the open Air, having a continual undulating Motion. This being plac'd under a Receiver, after some few Exclusions, the Undulation ceas'd, but the Luminous Quality appeared to be in a great measure increas'd; the Receiver being farther exaulted, it became manifestly brighter; and so continu'd, till on the Admission of Air (which was gradually done) the Light sensibly diminishing all the while. But upon the Repetition of the Experiment, it was the Opinion of those Gentlemen then present, that it did not appear altogether so brisk or so vivid as at first.

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