Structurally ferroelectric SrMgF4

2001 ◽  
Vol 58 (1) ◽  
pp. 34-37 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Crystal Structure ◽  
Curie Temperature ◽  
Spontaneous Polarization ◽  
Two Dimensional ◽  
Acta Cryst ◽  
Ferroelectric Switching

The crystal structure of 0.06% Ce-doped SrMgF4, strontium magnesium tetrafluoride, reported by Ishizawa et al. [(2001), Acta Cryst. C57, 784–786]  is shown to satisfy the structural criteria for ferroelectricity and to have a predicted Curie temperature T c ≃ l450 K. The estimated spontaneous polarization P s ≃ 11 × 10−2 C m−2 is consistent with classification as a two-dimensional ferroelectric in which minor Δx and major Δy, Δz atomic coordinate component displacements are required for ferroelectric switching.

scholarly journals Crystal structure of a trigonal polymorph of aquadioxidobis(pentane-2,4-dionato-κ2 O,O′)uranium(VI)

2022 ◽  
Vol 78 (1) ◽  
Author(s):  
Alejandro Hernandez ◽  
Indranil Chakraborty ◽  
Gabriela Ortega ◽  
Christopher J. Dares
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Water Molecule ◽  
Equatorial Plane ◽  
Title Compound ◽  
Uranium Atom ◽  
Intermolecular Hydrogen Bonding ◽  
Two Dimensional ◽  
Asymmetric Unit ◽  
Acta Cryst

The title compound, [UO2(acac)2(H2O)] consists of a uranyl(VI) unit ([O=U=O]2+) coordinated to two monoanionic acetylacetonate (acac, C5H7O2) ligands and one water molecule. The asymmetric unit includes a one-half of a uranium atom, one oxido ion, one-half of a water molecule and one acac ligand. The coordination about the uranium atom is distorted pentagonal–bipyramidal. The acac ligands and Ow atom comprise the equatorial plane, while the uranyl O atoms occupy the axial positions. Intermolecular hydrogen bonding between complexes results in the formation of two-dimensional hexagonal void channels along the c-axis direction with a diameter of 6.7 Å. The monoclinic (P21/c space group) polymorph was reported by Alcock & Flanders [(1987). Acta Cryst. C43, 1480–1483].

scholarly journals 2,2′-(Piperazine-1,4-diyl)diethanaminium dibenzoate

2012 ◽  
Vol 68 (8) ◽  
pp. o2389-o2389
Author(s):  
Ignacy Cukrowski ◽  
Adedapo S. Adeyinka ◽  
David C. Liles
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Intermolecular Interactions ◽  
Two Dimensional ◽  
Asymmetric Unit ◽  
Acta Cryst ◽  
Two Component ◽  
Anions And Cations ◽  
Benzoate Anion

The asymmetric unit of the title salt C8H22N42+·2C7H5O2−, comprises two independent pairs of half a 2,2′-(piperazine-1,4-diyl)diethanaminium dication plus a benzoate anion. The dications are symmetrical and lie across crystallographic centres of inversion. The crystal structure was refined as a two-component pseudo-merohedral twin using the twin law 001 0-10 100 [he domain fractions are 0.8645 (8) and 0.1355 (8)]. The anions and cations are linked by N—H...O hydrogen bonds and weak N—H...O intermolecular interactions to form infinite two-dimensional networks parallel to [101]. The conformation adopted by the cation in the crystal structure is very similar to that adopted by the same cation in the structures of the 2-hydroxybenzoate [Cukrowskiet al.(2012).Acta Cryst, E68, o2387], the nitrate and the tetrahydrogen pentaborate salts.

scholarly journals Crystal structure and Hirshfeld surface analysis of (E)-2-(5-bromo-2-hydroxybenzylidene)hydrazinecarbothioamide dimethyl sulfoxide monosolvate

2018 ◽  
Vol 74 (2) ◽  
pp. 119-123 ◽  
Author(s):  
Palaniyappan Sivajeyanthi ◽  
Muthaiah Jeevaraj ◽  
Bellarmin Edison ◽  
Kasthuri Balasubramani
Keyword(s):  
Crystal Structure ◽  
Schiff Base ◽  
Solid State ◽  
Hydrogen Bonds ◽  
Dimethyl Sulfoxide ◽  
Hirshfeld Surface ◽  
Two Dimensional ◽  
State Structure ◽  
Acta Cryst ◽  
The Mean

The molecule of the title Schiff base, C8H8BrN3OS·C2H6OS, which crystallizes as a dimethyl sulfoxide (DMSO) monosolvate, displays an E configuration with respect to the C=N bond, with a dihedral angle of 14.54 (11)° between the benzene ring and the mean plane of the N—N—C(N)=S unit. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming chains propagating along the b-axis direction. Within the chains there are R 2 3(11) ring motifs, which are reinforced by C—H...ODMSO hydrogen bonds enclosing secondary R 1 2(6) and R 2 3(9) loops. The chains are linked by O—Hhydroxyl...S hydrogen bonds, forming layers parallel to (011). Inversion-related layers are linked by short Br...Br interactions [3.5585 (5) Å], forming slabs parallel to (011). The intermolecular interactions have been investigated using Hirshfeld surface studies and two-dimensional fingerprint plots. The crystal structure of the unsolvated form of the title compound has been reported previously [Kargar et al. (2010). Acta Cryst. E66, o2999], and its solid-state structure is compared with that of the title solvated form.

scholarly journals Crystal structures of three functionalized chalcones: 4′-dimethylamino-3-nitrochalcone, 3-dimethylamino-3′-nitrochalcone and 3′-nitrochalcone

2020 ◽  
Vol 76 (10) ◽  
pp. 1599-1604
Author(s):  
Charlie L. Hall ◽  
Victoria Hamilton ◽  
Jason Potticary ◽  
Matthew E. Cremeens ◽  
Natalie E. Pridmore ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Crystal Structures ◽  
Functional Groups ◽  
Organic Molecules ◽  
Two Dimensional ◽  
Large Dataset ◽  
Acta Cryst ◽  
Small Organic Molecules ◽  
Hydrogen Bonding Interactions

The structure of three functionalized chalcones (1,3-diarylprop-2-en-1-ones), containing combinations of nitro and dimethylamino functional groups, are presented, namely, 1-[4-(dimethylamino)phenyl]-3-(3-nitrophenyl)prop-2-en-1-one, C17H16N2O3, Gp8m, 3-[3-(dimethylamino)phenyl]-1-(3-nitrophenyl)prop-2-en-1-one, C17H16N2O3, Hm7m and 1-(3-nitrophenyl)-3-phenylprop-2-en-1-one, C15H11NO3, Hm1-. Each of the molecules contains bonding motifs seen in previously solved crystal structures of functionalized chalcones, adding to the large dataset available for these small organic molecules. The structures of all three of the title compounds contain similar bonding motifs, resulting in two-dimensional planes of molecules formed via C—H...O hydrogen-bonding interactions involving the nitro- and ketone groups. The structure of Hm1- is very similar to the crystal structure of a previously solved isomer [Jing (2009). Acta Cryst. E65, o2510].

Prediction of ferroelectricity in recent Inorganic Crystal Structure Database entries under space group Pba2

1996 ◽  
Vol 52 (5) ◽  
pp. 806-809 ◽  
Author(s):  
S. C. Abrahams ◽  
K. Mirsky ◽  
R. M. Nielson
Keyword(s):  
Crystal Structure ◽  
Curie Temperature ◽  
Spontaneous Polarization ◽  
Ferroelectric Materials ◽  
Inorganic Crystal Structure Database ◽  
Space Group ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Atomic Coordinates ◽  
Crystal Structure Database

Three new entries in space group Pba2 in the 1995 edition of the Inorganic Crystal Structure Database have been examined in the light of previously developed criteria for the prediction of ferroelectricity. The structural prediction [Abrahams (1989). Acta Cryst. B45, 228–232] that seven of the 21 entries presented under this space group in the 1988 edition most likely corresponded to previously unrecognized ferroelectric materials is thereby updated. The atomic coordinates of [(NH2)2C(NHNH3)]ZrF6, among the new entries, are shown to satisfy the structural criteria; the maximum displacement along the polar axis required of any atom to undergo spontaneous polarization reversal is no larger than ~ 0.9 Å for a C or N atom and ~ 1.4 Å for a H atom, within the aminoguanidinium (2+) cation. By contrast, all atoms in the two independent ZrF6 anions are within 0.1 Å of an arrangement with zero spontaneous polarization. The characteristic force constant of the organic group is presently unknown, hence the Curie temperature for the crystal cannot be estimated. In the second new entry, the only atoms in the structure of the superconductor Ba0.6K0.4BiO23 at 403 K which depart significantly from a centrosymmetric arrangement are three of the four independent O atoms, one of which is at a site only 6% occupied. If these displacements are not artefacts, then this material is ferroelectric with an estimated Curie temperature in the range 410–740 K; a subsequent study, however, reported the structure in space group Pbam. The atomic coordinates of the final 1995 entry, (Cl3PNPCl3)(MoOCl4), do not differ significantly from centrosymmetry, in which case the material is not ferroelectic, apart from unequal occupancy of the Mo-atom sites. If the disorder model is correct and the two Mo sites are unequally occupied, then these sites cannot become equivalent and (Cl3PNPCl3)(MoOCl4) must remain polar without the possibility of becoming ferroelectric.

scholarly journals Ferromagnetism and giant magnetoresistance in zinc-blende FeAs monolayers embedded in semiconductor structures

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Le Duc Anh ◽  
Taiki Hayakawa ◽  
Yuji Nakagawa ◽  
Hikari Shinya ◽  
Tetsuya Fukushima ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Curie Temperature ◽  
First Principles ◽  
Giant Magnetoresistance ◽  
Two Dimensional ◽  
First Principles Calculations ◽  
Semiconductor Structures ◽  
Zinc Blende ◽  
Quantum Ground States

AbstractMaterial structures containing tetrahedral FeAs bonds, depending on their density and geometrical distribution, can host several competing quantum ground states ranging from superconductivity to ferromagnetism. Here we examine structures of quasi two-dimensional (2D) layers of tetrahedral Fe-As bonds embedded with a regular interval in a semiconductor InAs matrix, which resembles the crystal structure of Fe-based superconductors. Contrary to the case of Fe-based pnictides, these FeAs/InAs superlattices (SLs) exhibit ferromagnetism, whose Curie temperature (TC) increases rapidly with decreasing the InAs interval thickness tInAs (TC ∝ tInAs−3), and an extremely large magnetoresistance up to 500% that is tunable by a gate voltage. Our first principles calculations reveal the important role of disordered positions of Fe atoms in the establishment of ferromagnetism in these quasi-2D FeAs-based SLs. These unique features mark the FeAs/InAs SLs as promising structures for spintronic applications.

Cu(OH)2: a New Ferroelectric

1995 ◽  
Vol 28 (5) ◽  
pp. 594-598 ◽  
Author(s):  
S. C. Abrahams ◽  
J. Ravez ◽  
A. Simon ◽  
A. Reller ◽  
H. R. Oswald
Keyword(s):  
Crystal Structure ◽  
Heat Capacity ◽  
Ionic Conductivity ◽  
Curie Temperature ◽  
Room Temperature ◽  
Structural Transition ◽  
Wide Frequency Range ◽  
Dielectric Anomaly ◽  
Frequency Range ◽  
Acta Cryst

The crystal structure of Cu(OH)2, recently redetermined at room temperature by Oswald, Reller, Schmalle & Dubler [Acta Cryst. (1990), C46, 2279–2284], is shown to satisfy the structural criteria for ferroelectricity. The Cu2+ ion at 295 K is displaced 0.131 Å from the most likely paraelectric atomic arrangement, allowing the prediction to be made that the ferroelectric Curie temperature is Tc = 343 K. This prediction is in excellent agreement with an earlier report of a reversible structural transition at 325–335 K in Cu(OH)2. The presence of a λ-shaped anomaly in the heat capacity at about 335 K has been confirmed, and a dielectric anomaly is also observed at similar temperatures over a wide frequency range; the frequency dependence is dispersive, owing at least partly to ionic conductivity. The prediction is hence verified, and Cu(OH)2 is demonstrated experimentally to be a new ferroelectric.

scholarly journals Rational Design and Simulation of Two-Dimensional Perovskite Photonic Crystal Absorption Layers Enabling Improved Light Absorption Efficiency for Solar Cells

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2460
Author(s):  
Jian Zou ◽  
Mengnan Liu ◽  
Shuyu Tan ◽  
Zhijie Bi ◽  
Yong Wan ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Solar Cells ◽  
Photonic Crystal ◽  
Incident Light ◽  
Absorption Efficiency ◽  
Utilization Efficiency ◽  
Photonic Crystal Structure ◽  
Two Dimensional ◽  
Photoelectric Conversion ◽  
Absorption Layer

A two-dimensional perovskite photonic crystal structure of Methylamine lead iodide (CH3NH3PbI3, MAPbI3) is rationally designed as the absorption layer for solar cells. The photonic crystal (PC) structure possesses the distinct “slow light” and band gap effect, leading to the increased absorption efficiency of the absorption layer, and thus the increased photoelectric conversion efficiency of the battery. Simulation results indicate that the best absorption efficiency can be achieved when the scattering element of indium arsenide (InAs) cylinder is arranged in the absorption layer in the form of tetragonal lattice with the height of 0.6 μm, the diameter of 0.24 μm, and the lattice constant of 0.4 μm. In the wide wavelength range of 400–1200 nm, the absorption efficiency can be reached up to 82.5%, which is 70.1% higher than that of the absorption layer without the photonic crystal structure. In addition, the absorption layer with photonic crystal structure has good adaptability to the incident light angle, presenting the stable absorption efficiency of 80% in the wide incident range of 0–80°. The results demonstrate that the absorption layer with photonic crystal structure can realize the wide spectrum, wide angle, and high absorption of incident light, resulting in the increased utilization efficiency of solar energy.

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