Crystallization of amorphous boron by the calorimetric method

Machaladze, Tengiz; Samkharadze, Madona; Kakhidze, Nino; Махвиладзе, Array М.

doi:10.4236/ojic.2014.41003

Cited by 6 publications

(5 citation statements)

References 1 publication

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“…154) An old study by Decker and Kasper reported that, by heating α-R boron, a variety of unidentified phases appeared before obtaining β-R boron. 47) Similar results were reported by two recent studies, 153,155) showing that α-R boron is obtained at T < 1200 °C, while β-R boron by heating at T > 1600 °C. Between these temperatures, two unidentified phases were observed.…”

Section: Experimental Phase Diagramssupporting

confidence: 86%

“…The upper bound of α-R boron about T = 1200 °C agrees among different methods. 47,101,[151][152][153] Above T = 1200 °C, β-R boron is obtained. Runow observed a transition from α to β phase at an estimated temperature of 1370 °C.…”

Section: Experimental Phase Diagramsmentioning

confidence: 99%

“…Recent calorimetric measurements show that the reaction α → β at T t = 1600 °C is exothermic with the latent heat L = 64 meV=atom. 153,155) However, the second and third terms in Eq. ( 3) almost cancel this value of L, giving a small value of about 10 meV=atom for ΔH α,β .…”

Section: Experimental Phase Diagramsmentioning

confidence: 99%

“…It may be correct to say that α-R boron is a metastable phase at the transition temperature T t , by observing that the reaction α → β is an exothermic reaction. 153,155) However, it does not explain why α-R boron always precedes the growth of β-R boron below T t . For α-R boron, there may be special kinetics in the growth process, which is favorable for the low temperature growth.…”

Section: Experimental Phase Diagramsmentioning

confidence: 99%

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Phase diagram of boron crystals

Shirai

2017

Jpn. J. Appl. Phys.

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The current status of study on the phase diagram of boron is given from the theoretical viewpoint. Boron is the last elemental crystal whose phase diagram is missing. In the last decade, several new structures of boron allotropes were found, while some were disproven. Presently, even the number of allotropes of boron is uncertain. A simple reason for this is that there are many and complicated structures, and some are minimally different from the others. A theoretical study thus requires very high accuracy. The difficulty, however, is not merely a technical difficulty of computational scale. The physics involved is quite different from what is obtained by band theory, which is the most successful theory of solids. It is only recent that a fundamental problem of metal/insulator has been solved. We come to know that the interrelationships between nonstoichiometry, partially occupied sites, and the balance of intra/inter-icosahedral bonding, which were considered to be uncorrelated properties, inevitably determine the relative stability of various structures. The configuration of the defects in boron crystals is not capricious but there is some correlation among the defects. Many problems were solved on this ground, and contributed to the creation of the phase diagram. However, there are still many unsolved problems and some newly arose. In particular, for the tetragonal phase, sharp discrepancies are present in both experiment and theory. Thus, the problem of tetragonal phase is described in more detail. From the viewpoint of material research, the phase diagram provides the basis for searching new materials. State-of-the-art methods of structural prediction have stimulated researchers’ interest.

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Section: Experimental Phase Diagramssupporting

confidence: 86%

Section: Experimental Phase Diagramsmentioning

confidence: 99%

Section: Experimental Phase Diagramsmentioning

confidence: 99%

Section: Experimental Phase Diagramsmentioning

confidence: 99%

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Phase diagram of boron crystals

Shirai

2017

Jpn. J. Appl. Phys.

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“…The transition from amorphous boron to crystalline ¡-rhombohedral boron occurs above 1300°C. 22) It is thus considered that the reactivity among the YB 4 precursor, carbon and boron decreased when the mixture was kept at 1300°C due to the transition of amorphous boron to crystalline boron, and hence less YB 22 C 2 N was formed. Furthermore, the reaction rate is closely related to the surface area.…”

mentioning

confidence: 99%

Rapid synthesis of thermoelectric YB<sub>22</sub>C<sub>2</sub>N via spark plasma sintering with gas/solid reaction technology

Son

Sauerschnig

Berthebaud

et al. 2020

J. Ceram. Soc. Japan

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Dense YB 22 C 2 N samples were directly synthesized from powder mixtures via reactive spark plasma sintering. The gas/solid reaction step was applied to introduce nitrogen into the mixture during heating. The sample reactively sintered at 1700°C for 10 min after the gas/solid reaction step at 1200°C for 30 min consisted of YB 22 C 2 N with small amounts of secondary phases. The thermoelectric behavior shifted toward n-type behavior with increasing amount of YB 22 C 2 N phase. This newly developed synthesis technique could facilitate the rapid and cost-effective preparation of complex borocarbonitrides.

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