New ferromagnetic compound CaCo2 (C15) synthesized at high pressure

Tsvyashchenko, A. V.; Фомичева, Л.Н.; Magnitskaya, M. V.; Sidorov, V. A.; Kuznetsov, A. V.; Eremenko, D. V.; Trofimov, V. N.

doi:10.1134/1.567954

Cited by 16 publications

(15 citation statements)

References 31 publications

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“…A number of crystalline metastable phases, such as diamond, have the P,T-region of thermodynamic stability. Other metastable modifications like amorphous solids or fullerite C 60 have no stability region at any pressure and temperature. Some metastable substances like silicon clathrates seem to have conditional stability region at negative pressures.…”

Section: Obtain and Retainmentioning

confidence: 99%

“…The first examples of the systems with new compounds were the K-Ni, K-Ag, K-Pd systems [18]; however, the synthesis of these intermetallic compounds requires pressures of several tens of GPa. Another interesting example is the CaCo 2 compound, synthesized under a pressure of 5-7 GPa and possessing fascinating ferromagnetic characteristics such record Curie temperature for the substances of this class T c =528K (Co magnetic moment is 1.75 µB) at normal pressure [60]. …”

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High-pressure synthesized materials: treasures and hints

Бражкин

2007

High Pressure Research

108

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The present review covers the production of new materials under high pressures. A primary limitation on the use of pressures higher than 1 GPa is a small volume and mass of a produced material. Therefore, despite an extremely wide range of new high-pressure synthesized substances with unique properties, synthesis on an commercial scale is applied up to now only to obtain superhard materials, this real treasure of today's industry. At the same time, high-pressure experiments often give material scientists a hint at what new intriguing substances can exist in principle. This is true for new superhard, semiconducting, magnetic, superconducting and optical materials already synthesized under pressure, and as well as for a large number of hypothetic new polymers from low-Z elements. Many of new materials, including the above polymers, may exist in the metastable form at normal pressure at sufficiently high temperatures.Keywords: high pressure, materials synthesis, metastable phases 1 IntroductionThe synthesis of materials under high pressure is a vast area of physics, chemistry and engineering. Should you browse the Internet to search "high pressure synthesis", the web search engines, for example, Google, would respond with over 10 mln links, making it absolutely impossible to write any comprehensive review on this topic. For this same reason, neither it is possible to list all relevant references. The purpose of this paper is to present the author's personal view on the state of art and prospects of the production of new materials by using highpressure synthesis, and to complement already existing reviews, for example [1,2]. It should be noted that a number of publications, for example [2], discuss a comparatively narrow range of materials synthesized under pressure. Other publications, for example [1], also focus on anomalous properties of materials in a strongly compressed state, although most of materials with such properties cannot be retained at normal pressure, hence, they are not directly related to the subject under consideration. In addition, the behavior of materials in a strongly compressed state has also been extensively covered in scientific literature (for example, see [3]).For physicists, the history of a high-pressure research is first of all associated with P.W. Bridgman, a 1946 Nobel Prize Laureate "for the invention of an apparatus to produce extremely high pressures, and for the discoveries he made therewith in the field of high pressure physics". Nowadays high-pressure synthesis of new materials is primarily associated with a successful synthesis of superhard materials -diamond and cubic boron nitride -in the second half of the 20 th century. At the same time, the pressures 1 -10 3 MPa have been already in use for more than a century in chemistry for the industrial production of materials. What's more, the development of relevant engineering procedures has been more than once rewarded with a Nobel Prize in chemistry. In 1918, F. Haber won the Nobel Prize "for the synthesis of ammonia from its el...

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Section: Obtain and Retainmentioning

confidence: 99%

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High-pressure synthesized materials: treasures and hints

Бражкин

2007

High Pressure Research

108

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“…Phonon calculations for LiBe 4 , LiBe 2 and LiBe at 80 GPa reveal no imaginary frequencies, indicating these phases possess stable (local) minima. The most stable Li 3 Be phase has a soft mode, which leads to a unit cell doubling with a stabilization of less than 2 meV per atom.…”

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Emergent reduction of electronic state dimensionality in dense ordered Li-Be alloys

Feng

Hennig

Ashcroft

et al. 2008

Nature

124

109

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High pressure is known to influence electronic structure and crystal packing, and can in some cases even induce compound formation between elements that do not bond under ambient conditions [1][2][3] . Here we present a computational study showing that high pressure fundamentally alters the reactivity of the light elements lithium (Li) and beryllium (Be), which are the first of the metals in the condensed state and immiscible under normal conditions 4,5 . We identify four stoichiometric Li x Be 12x compounds that are stable over a range of pressures, and find that the electronic density of states of one of them displays a remarkable steplike feature near the bottom of the valence band and then remains almost constant with increasing energy. These characteristics are typical of a quasi-two-dimensional electronic structure, the emergence of which in a three-dimensional environment is rather unexpected. We attribute this observation to large size differences between the ionic cores of Li and Be: as the density increases, the Li cores start to overlap and thereby expel valence electrons into quasi-two-dimensional layers characterized by delocalized free-particle-like states in the vicinity of Be ions.Our extensive structural search exploring possible Be-Li compound formation under pressure uses two conceptually different approaches. In the first, we propose possible structures on the basis of established chemical/physical heuristics of alloy stability at 1 atmosphere (atm) and/or high pressure. Phenomenological 1-atm binary intermetallic structure maps 6 proved useful in this endeavour. In the second approach, initial structures are formed from randomly generated unit cells and atom positions, and subsequently optimized using density-functional theory (DFT) 7 , with the random search targeting unit cells with 15 or fewer atoms. This combined staticlattice structure search explores the stoichiometries most common in binary intermetallic compounds, including LiBe, LiBe

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“…When the R-site is replaced by Ti, the d-electron number increases and the Fermi level E F shifts toward a higher energy side far from main peak of DOS, resulting in a paramagnetic TiCo 2 [13]. On the other hand, E F shifts to lower energy side by replacing R by Ca, and E F is located at just on the main peak of DOS [13], stabilizing the ferromagnetic state in CaCo 2 [14]. For the systems substituted the R-site in CaCo 2 , ScCo 2 and TiCo 2 , a rigid band like concept is valid.…”

Section: Introductionmentioning

confidence: 91%