Tetragonal metal

Tetragonal metal

The Jahn—Teller effect JT effect or JTE is an important mechanism of spontaneous symmetry breaking in molecular and solid-state systems which has far-reaching consequences in different fields, and is responsible for a variety of phenomena in spectroscopystereochemistrycrystal chemistrymolecular and solid-state physicsand materials science.

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The effect is named for Hermann Arthur Jahn and Edward Tellerwho first reported studies about it in The Jahn—Teller effectsometimes also referred to as Jahn—Teller distortiondescribes the geometrical distortion of molecules and ions that result from certain electron configurations. The Jahn—Teller theorem essentially states that any non-linear molecule with a spatially degenerate electronic ground state will undergo a geometrical distortion that removes that degeneracy, because the distortion lowers the overall energy of the species.

For a description of another type of geometrical distortion that occurs in crystals with substitutional impurities see article off-center ions. The Jahn—Teller effect is most often encountered in octahedral complexes of the transition metals. Such complexes distort along one of the molecular fourfold axes always labelled the z axiswhich has the effect of removing the orbital and electronic degeneracies and lowering the overall energy.

The distortion normally takes the form of elongating the bonds to the ligands lying along the z axis, but occasionally occurs as a shortening of these bonds instead the Jahn—Teller theorem does not predict the direction of the distortion, only the presence of an unstable geometry.

tetragonal metal

When such an elongation occurs, the effect is to lower the electrostatic repulsion between the electron-pair on the Lewis basic ligand and any electrons in orbitals with a z component, thus lowering the energy of the complex. The inversion centre is preserved after the distortion. In octahedral complexes, the Jahn—Teller effect is most pronounced when an odd number of electrons occupy the e g orbitals.

This situation arises in complexes with the configurations d 9low-spin d 7 or high-spin d 4 complexes, all of which have doubly degenerate ground states. In such compounds the e g orbitals involved in the degeneracy point directly at the ligands, so distortion can result in a large energetic stabilisation.

tetragonal metal

Strictly speaking, the effect also occurs when there is a degeneracy due to the electrons in the t 2g orbitals i. In such cases, however, the effect is much less noticeable, because there is a much smaller lowering of repulsion on taking ligands further away from the t 2g orbitals, which do not point directly at the ligands see the table below.

The same is true in tetrahedral complexes e. It is readily apparent in the structures of many copper II complexes. The underlying cause of the Jahn—Teller effect is the presence of molecular orbitals that are both degenerate and open shell i. This situation is not unique to coordination complexes and can be encountered in other areas of chemistry. In organic chemistry the phenomenon of antiaromaticity has the same cause and also often sees molecules distorting; as in the case of cyclobutadiene [5] and cyclooctatetraene COT.

Spin-degeneracy was an exception in the original treatment and was later treated separately.

Jahn–Teller effect

The formal mathematical proof of the Jahn—Teller theorem rests heavily on symmetry arguments, more specifically the theory of molecular point groups. The argument of Jahn and Teller assumes no details about the electronic structure of the system. Jahn and Teller made no statement about the strength of the effect, which may be so small that it is immeasurable.Tetragonal systemone of the structural categories to which crystalline solids can be assigned.

Crystals in this system are referred to three mutually perpendicular axestwo of which are equal in length. If the atoms or atom groups in the solid are represented by points and the points are connected, the resulting lattice will consist of an orderly stacking of blocks, or unit cells.

The elements boron and tin can crystallize in tetragonal form, as can some minerals such as zircon. Tetragonal system. Article Media. Info Print Cite. Submit Feedback. Thank you for your feedback. Tetragonal system crystallography. See Article History. Learn More in these related Britannica articles:. The orthorhombic and tetragonal systems also contain three mutually perpendicular axes; in the former system all the axes are of different lengths aband cand in the latter system two axes are of equal length a 1 and a 2 while the third vertical axis is either longer….

Chemical formulas and crystal-system data for a few of the feldspathoids are given in the Table. Optically uniaxial crystals tetragonal, hexagonal, and rhombohedral [or trigonal] systemswhich exhibit double refraction and yield two refractive indices for light of each colour, one parallel to the optical axis and one perpendicular to the optical axis;…. History at your fingertips. Sign up here to see what happened On This Dayevery day in your inbox!

Email address. By signing up, you agree to our Privacy Notice. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. More About.For elements that are solid at standard temperature and pressure the table gives the crystalline structure of the most thermodynamically stable form s in those conditions. In all other cases the structure given is for the element at its melting point. Data is presented only for the first elements as well as the th hydrogen through flerovium and oganessonand predictions are given for elements that have never been produced in bulk astatinefranciumand elements — and Among the undiscovered elements, predictions are only available for ununennium and unbinilium eka-francium and eka-radiumwhich are predicted to crystallise in body-centered cubic structures like their lighter congeners.

Many metals adopt close packed structures i. A simple model for both of these is to assume that the metal atoms are spherical and are packed together in the most efficient way close packing or closest packing.

In closest packing every atom has 12 equidistant nearest neighbours, and therefore a coordination number of If the close packed structures are considered as being built of layers of spheres then the difference between hexagonal close packing and face-centred cubic is how each layer is positioned relative to others.

Whilst there are many ways that can be envisaged for a regular buildup of layers:. For the four known actinides dhcp lattices the corresponding number vary between 1. This is not a close packed structure. From Wikipedia, the free encyclopedia. Crystal structure of elements in the periodic table. BCC : body-centered cubic. FCC : face-centered cubic cubic close packed. HCP : hexagonal close packed. DHCP : double hexagonal close packed.

ORTH : orthorhombic. TETR : tetragonal. RHO : rhombohedral. HEX : hexagonal. SC : simple cubic. DC : diamond cubic.

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MON : monoclinic. Chemistry of the Elements 2nd ed. Archived from the original on Retrieved Periodic table. Alternatives Janet's left step table. Lists of metalloids by source Dividing line. Reactive nonmetals Noble gases. Crystal structure Electron configuration Electronegativity Goldschmidt classification Term symbol. Element discoveries Mendeleev's predictions Naming etymology controversies for places for people in East Asia.

Book Category. Categories : Periodic table. Hidden categories: CS1 maint: archived copy as title. Namespaces Article Talk. Views Read Edit View history. Languages Add links.Continue to access RSC content when you are not at your institution. Follow our step-by-step guide. Two-dimensional 2D metal shrouded crystals, a new kind of conceptional material, have attracted remarkable attention due to their unique properties.

Here, we propose a novel class of 2D metal shrouded materials, tetragonal transition-metal phosphides TM 2 Pswhich show peculiar features of coexistence of in-plane TM—P covalent bonds and TM—TM interlayer metallic bonds.

From a combination of high throughput searching and first-principles calculations, Fe 2 P, Co 2 P, Ni 2 P, Ru 2 P, and Pd 2 P monolayer sheets stand out because they simultaneously have high thermal, dynamical, and mechanical stability. All these five TM 2 P materials are metals, especially Pd 2 P, which can be a promising catalyst for the hydrogen evolution reaction with a very low overpotential.

Even in the large strain range, the strengthened interlayer TM—TM metallic bonds dominate the deformation behavior, and the corresponding metallicity of 2D TM 2 Ps is well preserved.

Due to the competition between the d—d direct exchange and d—p—d superexchange interactions, Fe 2 P behaves as an antiferromagnetic material with a T N of 23 K, while Co 2 P is a ferromagnetic material with a T C of K.

Our results not only enrich the database of 2D metal shrouded crystals, but also provide novel 2D materials as promising candidates for multifunctional applications in nanoelectronics, spintronics and electrocatalysis. If you are not the author of this article and you wish to reproduce material from it in a third party non-RSC publication you must formally request permission using Copyright Clearance Center.

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Tetragonal system

Access to RSC content. You do not have JavaScript enabled. Please enable JavaScript to access the full features of the site or access our non-JavaScript page.Tantalum is a chemical element with the symbol Ta and atomic number Previously known as tantaliumit is named after Tantalusa villain from Greek mythology.

It is part of the refractory metals group, which are widely used as minor components in alloys. The chemical inertness of tantalum makes it a valuable substance for laboratory equipment, and as a substitute for platinum. Its main use today is in tantalum capacitors in electronic equipment such as mobile phonesDVD playersvideo game systems and computers.

Tantalum, always together with the chemically similar niobiumoccurs in the mineral groups tantalitecolumbite and coltan a mix of columbite and tantalite, though not recognised as a separate mineral species. Tantalum was discovered in Sweden in by Anders Ekebergin two mineral samples — one from Sweden and the other from Finland.

He concluded that the two oxides, despite their difference in measured density, were identical and kept the name tantalum. This conclusion was disputed in by the German chemist Heinrich Rosewho argued that there were two additional elements in the tantalite sample, and he named them after the children of Tantalus : niobium from Niobethe goddess of tearsand pelopium from Pelops.

tetragonal metal

The differences between tantalum and niobium were demonstrated unequivocally in by Christian Wilhelm Blomstrand[13] and Henri Etienne Sainte-Claire Devilleas well as by Louis J. Troostwho determined the empirical formulas of some of their compounds in These discoveries did not stop scientists from publishing articles about the so-called ilmenium until Wires made with metallic tantalum were used for light bulb filaments until tungsten replaced it in widespread use.

The name tantalum was derived from the name of the mythological Tantalusthe father of Niobe in Greek mythology. In the story, he had been punished after death by being condemned to stand knee-deep in water with perfect fruit growing above his head, both of which eternally tantalized him. If he bent to drink the water, it drained below the level he could reach, and if he reached for the fruit, the branches moved out of his grasp.

For decades, the commercial technology for separating tantalum from niobium involved the fractional crystallization of potassium heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, a process that was discovered by Jean Charles Galissard de Marignac in This method has been supplanted by solvent extraction from fluoride-containing solutions of tantalum. Tantalum is dark blue-gray[21] dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity.

It can be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulfur trioxideas well as with a solution of potassium hydroxide. Tantalum exists in two crystalline phases, alpha and beta. Bulk tantalum is almost entirely alpha phase, and the beta phase usually exists as thin films [22] obtained by magnetron sputteringchemical vapor deposition or electrochemical deposition from an eutectic molten salt solution.

Natural tantalum consists of two isotopes : m Ta 0. However, radioactivity of this nuclear isomer has never been observed, and only a lower limit on its half-life of 2. It is also the rarest primordial isotope in the Universe, taking into account the elemental abundance of tantalum and isotopic abundance of m Ta in the natural mixture of isotopes and again excluding radiogenic and cosmogenic short-lived nuclides.

Tantalum has been examined theoretically as a " salting " material for nuclear weapons cobalt is the better-known hypothetical salting material. An external shell of Ta would be irradiated by the intensive high-energy neutron flux from a hypothetical exploding nuclear weapon. This would transmute the tantalum into the radioactive isotope Ta, which has a half-life of Such "salted" weapons have never been built or tested, as far as is publicly known, and certainly never used as weapons.

Tantalum can be used as a target material for accelerated proton beams for the production of various short-lived isotopes including 8 Li, 80 Rb, and Yb. Most commonly encountered are oxides of Ta Vwhich includes all minerals. The chemical properties of Ta and Nb are very similar. Like niobium, tantalum is barely soluble in dilute solutions of hydrochloricsulfuricnitric and phosphoric acids due to the precipitation of hydrous Ta V oxide.

Tantalum pentoxide Ta 2 O 5 is the most important compound from the perspective of applications.Using optimized structural analysis, it is shown that the ground state of these all- d -metal Heusler alloys does not fully meet the site-preference rule for classic full-Heusler alloys. All the Mn-rich type alloys tend to form the L2 1 structure, where the two Mn atoms prefer to occupy the A 0, 0, 0 and C 0. The Mn-rich Heusler alloys have strong cubic resistance; however, all the Mn-poor alloys prefer to have a tetragonal state instead of a cubic phase through tetragonal transformations.

The origin of the tetragonal state and the competition between the cubic and tetragonal phases in Mn-poor alloys are discussed in detail. Furthermore, the lack of virtual frequency in the phonon spectra confirms the stability of the tetragonal states of these Mn-poor all- d -metal Heusler alloys.

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This work provides relevant experimental guidance in the search for possible martensitic Heusler alloys in all- d -metal materials with less Mn and new spintronic and magnetic intelligent materials among all- d -metal Heusler alloys. Keywords: all- d -metal Heusler alloys ; tetragonal deformation ; computational modelling ; density functional theory.

Heusler alloys have been a research hotspot for more than years, gaining the attention of researchers due to their excellent properties and wide range of applications. High Curie temperatures T Ctunable electronic structure, suitable lattice constants for semiconductors and various magnetic properties Manna et al.

However, some new Heusler alloys have emerged, adding novel theoretical and experimental findings to Heusler's research. Recently, Wei et al. Wei et al. Based on this experimental work Wei et al. We must note, however, that research on this aspect is very rare. Recently, some interesting work brought to our attention by Tan et al. Therefore, searching for new magnetic all- d -metal Heusler alloys and investigating their site occupation is necessary.

Examining recent studies of Heusler alloys, researchers emphasized the cubic state over the tetragonal phase, which limits progress in finding better tetragonal Heusler alloys. However, tetragonal phases are more likely to demonstrate large perpendicular magnetic anisotropy than the cubic state — the key to spin-transfer torque devices Balke et al.

Additionally, tetragonal states have large magneto-crystalline anisotropy Salazar et al. To better apply Heusler alloys to actual fields, it is also important to study their tetragonal state and the competition between cubic and tetragonal states.

Our goals were to further strengthen the study of all- d -metal Heusler alloys and investigate their magnetic properties, electronic structures and site preference via first principles. We provide an in-depth discussion of their tetragonal transformations to find a stable tetragonal phase in the search for better applications in spintronics.

We also explain and prove the stability of the tetragonal phases with the help of density of states DOS and phonon spectra. To describe the interaction between electron-exchange-related energy and the nucleus and valence electrons, the Perdew—Burke—Ernzerhof function of the generalized gradient approximation Perdew et al.

The site-preference rule Luo et al. When the X atoms carry the most valence electrons, X tends to occupy the A 0, 0, 0 and C 0. The Z atoms, having the least valence electrons, tend to be located at the D site 0. The full-Heusler alloys consist of both transition-metal elements and main-group elements; however, the situation is not the same as in all- d -metal Heusler alloys.

All- d -metal Heusler alloys are composed entirely of transition-metal elements without main-group atoms, so they do not necessarily conform to the site-preference rule.

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The desired properties depend strongly on a highly ordered structure. Another situation is the L2 1 type. However, when the total energy difference between XA and L2 1 phases is quite small, the two states may co-exist. X atoms tend toward the A and C sites, and Mn prefers the B sites. However, in our calculations, the Mn-rich alloys fully disobey the site-preference rule, and some Mn-poor types meet the rule whereas others do not, suggesting that the site-preference rule does not apply to all of the all- d -metal Heusler alloys.

Finally, we come to study the magnetic properties of these alloys in the cubic phase; the total magnetic moments of these all- d -metal Heusler alloys are shown in Table 1.These metrics are regularly updated to reflect usage leading up to the last few days.

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Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online.

Clicking on the donut icon will load a page at altmetric. Find more information on the Altmetric Attention Score and how the score is calculated. Each compound adopts a different antiferromagnetic AFM ordering of local moments associated with the 3d metal sites, but every one involves a doubled crystallographic c -axis. Effective exchange parameters obtained from SPRKKR calculations indicate that both direct and indirect exchange couplings play essential roles in understanding the different magnetic orderings observed.

Interestingly, the magnetic structures of Fe 2 As and Mn 2 As show tetragonal symmetry, but a magnetostrictive tetragonal-to-orthorhombic distortion could occur in Cr 2 As through AFM Cr1—Cr2 coupling between symmetry inequivalent Cr atoms along the a -axis, but FM coupling along the b -axis.

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tetragonal metal

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