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Orthorhombic crystal system

About: Orthorhombic crystal system is a research topic. Over the lifetime, 26421 publications have been published within this topic receiving 471993 citations. The topic is also known as: orthorhombic.


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Journal ArticleDOI
TL;DR: In this paper, a Mg-Y-Nd-based alloy (WE54) was characterised using transmission electron microscopy and the formation of three separate metastable phases, α platelets of an as yet unidentified phase, and the phases designated β′ and β1, preceding formation of the equilibrium phase β.

663 citations

Journal ArticleDOI
26 Feb 1988-Science
TL;DR: A new superconductor that displays onset behavior near 120 K has been identified as Bi2Sr3-xCaxCu2O8+y, with x ranging from about 0.4 to 0.9, and electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension.
Abstract: A new superconductor that displays onset behavior near 120 K has been identified as Bi2Sr3-xCaxCu2O8+y, with x ranging from about 0.4 to 0.9. Single crystal x-ray diffraction data were used to determine a pseudo-tetragonal structure based on an A-centered orthorhombic subcell with a = 5.399 A, b= 5.414A, and c = 30.904 A. The structure contains copper-oxygen sheets as in La2CuO4 and YBa2Cu3O7, but the copper-oxygen chains present in YBa2Cu3O7 do not occur in Bi2Sr3-xCaxCu2O8+y. The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca2+ and Sr2+ cations between the adjacent Cu-O sheets; Sr2+ cations are also found between the Cu-O and Bi-O sheets. Electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension. This superstructure is also observed by x-ray diffraction on single crystals, but twinning can make it appear that the superstructure is along both a and b axes. Flux exclusion begins in our samples at about 116 K and is very strong by 95 K. Electrical measurements on a single crystal of Bi2Sr3-xCaxCu2O8+y show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.

623 citations

Journal ArticleDOI
TL;DR: In this article, a quasi-topotactic intercalation mechanism was proposed, in which lithium is inserted into monoclinic binary MnP4 to form the cubic ternary Li7MnP4 phase.
Abstract: Lithium-ion rechargeable batteries are used as portable power sources for a wide variety of electronic devices, such as cellular phones, notebook computers, and camcorders. Intensive research efforts have been made over the past decade to increase the gravimetric and volumetric energy density of lithium ion batteries. At present, graphite (372 mAhg) is used as an anode material for lithium ion batteries, but higher capacity alternatives are being actively pursued. Among the many possible alternatives, a lot of work has been devoted to Sn-based oxide, Si-based composite, transition metal oxide, metal nitride and metal phosphide systems, due to their ability to react reversibly with large amounts of Li per formula unit. Although alloy-based systems have a higher energy density, they suffer from poor capacity retention, since a large volume change occurs during charge/discharge. Among these alternatives, a concept based on the quasi-topotactic intercalation mechanism was proposed, in which lithium is inserted into monoclinic binary MnP4 to form the cubic ternary Li7MnP4 phase. [10] Since then, Li insertion/extraction in transition metal phosphides has been investigated as a possible candidate for the anode material in lithium ion batteries. In these systems, commercial red P and transition metals were used to synthesize metal phosphides, but the energy density is reduced due to the heavy transition metals employed. If phosphorus were used for electrode materials, it would have a good energy density, but little is known about its electrochemical behavior, since commercial red P has an amorphous structure with a poor bulk conductivity and poor cyclability. Phosphorus, an element of the fifth group in the periodic table, has three main allotropes: white, red, and black. Among these modifications of allotropes, black phosphorus is thermodynamically the most stable, insoluble in most solvents, practically non-flammable, and chemically the least reactive form, and exists in three known crystalline modifications (orthorhombic, rhombohedral, and simple cubic), as well as in an amorphous form. Since orthorhombic black phosphorus was obtained from white phosphorus at 200 C and 1.2 GPa, many studies designed to synthesize black phosphorus have been reported. However, the basic concept of a high temperature and high pressure being required has not been changed, and black phosphorus still remains difficult to synthesize, and has the lowest commercial value of the three forms. Considering that orthorhombic black phosphorus exhibits a layer structure similar to that of graphite, which is currently used as an anode material for Li ion batteries, we developed a simple method of transforming commercially available amorphous red phosphorus into orthorhombic black phosphorus using a high energy mechanical milling (HEMM) technique at ambient temperature and pressure. It is known that the temperature during HEMM can rise above 200 C and the pressure generated can be of the order of 6 GPa. These conditions should be sufficient to transform red P into its high-pressure allotrope, the black phosphorus phase, at ambient temperature and pressure. Figure 1a shows the color photo image, XRD pattern, and TEM electron diffraction pattern showing a diffuse ring of red P, which confirms the amorphous nature of the red P. The sample prepared by HEMM corresponds to orthorhombic black P according to the XRD data and color photo image (Fig. 1b), and was also identified by high resolution TEM electron diffraction, and by its lattice spacing. Figure 2a and 2b show the voltage profiles of red P and black P, respectively. Their electrochemical behaviors are very different from each other. The discharge and charge capacities of red P are 1692 and 67 mAhg, respectively, and it cannot be used as an anode material since its charge capacity is negligible. Although black P shows an increased charge capacity of 1279 mAhg, the first cycle efficiency is only 57%. The electrochemical performance of Si as an anode material for Li ion batteries can be much improved using Si–carbon composites. Black P also has a low electronic conductivity inherited from its characteristic as a semiconductor. The electrochemical behaviors of the black P-carbon composite during the discharge/charge reaction with Li were excellent compared with the above two cases, as shown in Figure 2c. The first discharge and charge capacities are 2010 and 1814 mAhg, respectively, and the first cycle efficiency is about 90%, which is one of the highest reported. The good coulombic efficiency of the black P–carbon composite for the C O M M U N IC A IO N

619 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed an extension of Thomsen's anisotropy coefficients to orthorhombic models for seismic inversion and processing for anisotropic media.
Abstract: Although orthorhombic (or orthotropic) symmetry is believed to be common for fractured reservoirs, the difficulties in dealing with nine independent elastic constants have precluded this model from being used in seismology. A notation introduced in this work is designed to help make seismic inversion and processing for orthorhombic media more practical by simplifying the description of a wide range of seismic signatures. Taking advantage of the fact that the Christoffel equation has the same form in the symmetry planes of orthorhombic and transversely isotropic (TI) media, we can replace the stiffness coefficients by two vertical (P and S) velocities and seven dimensionless parameters that represent an extension of Thomsen's anisotropy coefficients to orthorhombic models. By design, this notation provides a uniform description of anisotropic media with both orthorhombic and TI symmetry. The dimensionless anisotropic parameters introduced here preserve all attractive features of Thomsen notation in treatin...

607 citations

Journal ArticleDOI
TL;DR: Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high-Tc phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate as mentioned in this paper.
Abstract: Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high-Tc phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate. The sharp powder X-ray diffraction pattern obtained from well-grown particles, 5~10 µm wide and 0.5 µm thick typically, was assigned to an orthorhombic cell with a=0.537 nm, b=2.682 nm, and c=3.726 nm. The electrical resistance dropped to zero at 107 K within the experimental limit of 10-6 Ω. A large diamagnetic response in the ac susceptibility due to the Meissner effect was seen below 120 K. The dominance of the high-Tc phase over the low-Tc phase was roughly estimated at 9/1 in volume.

579 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,010
20221,918
2021779
2020797
2019830
2018847