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Monoclinic crystal system

About: Monoclinic crystal system is a research topic. Over the lifetime, 27019 publications have been published within this topic receiving 442766 citations. The topic is also known as: monoclinic.


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TL;DR: In this paper, highly crystalline monoclinic and tetragonal BiVO4 photocatalysts were obtained by the reaction of layered potassium vanadate powder (KV3O8 and K3V5O14) with Bi(NO3)3 for 3 days in aqueous media at room temperature.
Abstract: BiVO4 photocatalysts for O2 evolution, which work under visible light irradiation, were prepared by an aqueous process. The BiVO4 photocatalysts were obtained by the reaction of layered potassium vanadate powder (KV3O8 and K3V5O14) with Bi(NO3)3 for 3 days in aqueous media at room temperature. Highly crystalline monoclinic and tetragonal BiVO4 were selectively synthesized by changing the ratio of vanadium to bismuth in the starting materials. X-ray diffraction and scanning electron microscopy measurements showed that the monoclinic BiVO4 was formed via a tetragonal BiVO4 intermediate. Tetragonal BiVO4 with a 2.9 eV band gap mainly possessed an ultraviolet absorption band while monoclinic BiVO4 with a 2.4 eV band gap had a characteristic visible light absorption band in addition to the UV band. The UV bands observed in the tetragonal and monoclinic BiVO4 were assigned to the band transition from O2p to V3d whereas the visible light absorption was due to the transition from a valence band formed by Bi6s or ...

1,761 citations

Journal ArticleDOI
TL;DR: Analysis of the hydration process by solid-state NMR has clearly indicated that the trapped water molecules interact with the carboxylate groups through hydrogen bonds, but do not affect the hydroxyl species bridging the aluminum atoms.
Abstract: Aluminum 1,4-benzenedicarboxylate Al(OH)[O2CC6H4CO2]⋅ [HO2CC6H4CO2H]0.70 or MIL-53 as (Al) has been hydrothermally synthesized by heating a mixture of aluminum nitrate, 1,4-benzenedicarboxylic acid, and water, for three days at 220 °C. Its 3 D framework is built up of infinite trans chains of corner-sharing AlO4(OH)2 octahedra. The chains are interconnected by the 1,4-benzenedicarboxylate groups, creating 1 D rhombic-shaped tunnels. Disordered 1,4-benzenedicarboxylic acid molecules are trapped inside these tunnels. Their evacuation upon heating, between 275 and 420 °C, leads to a nanoporous open-framework (MIL-53 ht (Al) or Al(OH)[O2CC6H4CO2]) with empty pores of diameter 8.5 A. This solid exhibits a Langmuir surface area of 1590(1) m2 g−1 together with a remarkable thermal stability, since it starts to decompose only at 500 °C. At room temperature, the solid reversibly absorbs water in its tunnels, causing a very large breathing effect and shrinkage of the pores. Analysis of the hydration process by solid-state NMR (1H, 13C, 27Al) has clearly indicated that the trapped water molecules interact with the carboxylate groups through hydrogen bonds, but do not affect the hydroxyl species bridging the aluminum atoms. The hydrogen bonds between water and the oxygen atoms of the framework are responsible for the contraction of the rhombic channels. The structures of the three forms have been determined by means of powder X-ray diffraction analysis. Crystal data for MIL-53 as (Al) are as follows: orthorhombic system, Pnma (no. 62), a = 17.129(2), b = 6.628(1), c = 12.182(1) A; for MIL-53 ht (Al), orthorhombic system, Imma (no. 74), a = 6.608(1), b = 16.675(3), c = 12.813(2) A; for MIL-53 lt (Al), monoclinic system, Cc (no. 9), a = 19.513(2), b = 7.612(1), c = 6.576(1) A, β = 104.24(1)°.

1,737 citations

Journal ArticleDOI
TL;DR: In this paper, first principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c.
Abstract: First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c. Our calculation indicates that the P2(1)/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414 A. These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P2(1)/c. The calculated bulk modulus of 373 GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357 GPa within 4.3% and of 402 GPa within 7.8%, but smaller than the experimental value of 428 GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2. For IrN3, cubic skutterudite structure (Im-3) was assumed.

1,646 citations

Journal ArticleDOI
TL;DR: TREOR as discussed by the authors is an indexing program based on trial-and-error methods that contains separate routines for cubic, tetragonal, hexagonal, orthorhombic, monoclinic and triclinic symmetries.
Abstract: An indexing program, TREOR, mainly based on trial-and-error methods is described. The program contains separate routines for cubic, tetragonal, hexagonal, orthorhombic, monoclinic and triclinic symmetries. Ten years usage has been analysed to improve the original program. For monoclinic indexing a specific short-axis test has been developed. The over-all success rate of the program has been found to be better than 90%, and considerably more for orthorhombic and higher symmetries.

1,645 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that crystalline phases with ferroelectric behavior can be formed in thin thin films of SiO2 doped hafnium oxide, which is suitable for field effect transistors and capacitors due to its excellent compatibility to silicon technology.
Abstract: We report that crystalline phases with ferroelectric behavior can be formed in thin films of SiO2 doped hafnium oxide. Films with a thickness of 10 nm and with less than 4 mol. % of SiO2 crystallize in a monoclinic/tetragonal phase mixture. We observed that the formation of the monoclinic phase is inhibited if crystallization occurs under mechanical encapsulation and an orthorhombic phase is obtained. This phase shows a distinct piezoelectric response, while polarization measurements exhibit a remanent polarization above 10 μC/cm2 at a coercive field of 1 MV/cm, suggesting that this phase is ferroelectric. Ferroelectric hafnium oxide is ideally suited for ferroelectric field effect transistors and capacitors due to its excellent compatibility to silicon technology.

1,631 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,016
20222,128
2021730
2020774
2019812
2018870