Disorder and Long‐Range Order in Non‐Stoichiometric Interstitial Compounds Transition Metal Carbides, Nitrides, and Oxides

Гусев, А. И.

doi:10.1002/pssb.2221630102

Cited by 142 publications

(208 citation statements)

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“…But, a disordered state is realized as the substance is subjected to normal cooling subsequent to high-temperature synthesis and most of the experimental work deals with the disordered phases. 11 Melting point of both V 2 N 1−x ᮀ x and VN 1−x ᮀ x are known to be well above 2000 K. Experimental formation enthalpy of VN 1−x ᮀ x is known for 1700 K. In the Monte Carlo simulations, we compute the formation enthalpy of the disordered phases at T = 2000 K. For ⑀-Fe 2 N-type V 2 N 1−x ᮀ x , our MC simulation used a 22ϫ 22ϫ 21 supercell with 60 984 V sites and 30 492 N sites making up a total of 91 476 sites. Onethird of the 30 492 N sites, i.e., 10 164, are active sites for sampling with ᮀ / N. For NaCl-type phase, a 22ϫ 22ϫ 22 supercell was used.…”

Section: B Cluster Expansion and Phase Stabilitymentioning

confidence: 99%

“…10 Properties of these nitrides are known to depend strongly on their chemistry and structural state. 11,12 The ground-state properties and phase stability of some of these phases have been studied in a previous work 13 via density functional theory ͑DFT͒ based electronic-structure totalenergy calculations. Based on the calculated formation enthalpies, it is shown that stoichiometric V 2 N is polymorphic in ⑀-Fe 2 N, -Fe 2 N, and Fe 2 C structures within a few meV.…”

Section: Introductionmentioning

confidence: 99%

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Cluster expansion Monte Carlo study of phase stability of vanadium nitrides

et al. 2010

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Phase stability of stable and metastable vanadium nitrides is studied using density functional theory ͑DFT͒ based total-energy calculations combined with cluster expansion Monte Carlo simulation and supercell methods. We have computed the formation enthalpy of the various stable and metastable vanadium nitride phases considering the available structural models and found that the formation enthalpies of the different phases decrease in the same order as they appear in the experimental aging sequence. DFT calculations are known to show stoichiometric V 2 N to be polymorphic in ⑀-Fe 2 N and -Fe 2 N structures within a few meV and VN to be more stable in WC͑B h ͒ phase than in the experimentally observed NaCl͑B1͒ structure. As these nitrides are known to be generally nonstoichiometric due to presence of nitrogen vacancies, we used cluster expansion and supercell methods for examining the effect of nitrogen vacancies on the phase stability. It is found that nitrogen vacancies, represented by ᮀ, stabilize ⑀-Fe 2 N phase of V 2 N 1−x ᮀ x and NaCl͑B1͒ phase of VN 1−x ᮀ x compared to -Fe 2 N and WC͑B h ͒ phases respectively, rendering the computed phase stability scenario to be in agreement with experiments. Analysis of supercell calculated electronic density of states ͑DOS͒ of VN 1−x ᮀ x with varying x, shows that the nitrogen vacancies increase the DOS at Fermi level in WC phase, whereas they decrease the DOS in NaCl phase. And this serves as the mechanism of enhancement of the stability of the NaCl phase. Monte Carlo simulations were used for computing the finite temperature formation enthalpies of these phases as a function of nitrogen-vacancy concentration and found close agreement for NaCl͑B1͒ phase of VN 1−x ᮀ x for which measured values are available.

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Section: B Cluster Expansion and Phase Stabilitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Cluster expansion Monte Carlo study of phase stability of vanadium nitrides

et al. 2010

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“…гр. Fm3m) карбидов NbC 0.77 , NbC 0.84 , NbC 0.93 и NbC 0.96 со структурой B1 были синтезированы высокотемператур-ным твердофазным вакуумным спеканием [7] авторами работы [13] по запатентованной методике [14]. Порошки содержат как крупные частицы размером до 4−6 µm, так и мелкие частицы размером 500 nm и менее.…”

Section: образцы и экспериментальные методыunclassified

“…В нестехиометрических карбидах MC y структурные вакансии содержатся только в углеродной (неметалли-ческой) подрешетке, но в нестехиометрических кубиче-ских монооксидах титана, ванадия и ниобия M x O z вакан-сии могут содержаться в кислородной и металлической подрешетках одновременно [7].…”

Section: влияние размера частиц на измеряемую плотность нанопорошковunclassified

“…гр. Fm3m) структурой B1 обладает широкой областью гомогенно-сти от NbC 0.72 до NbC 1.00 [7] и входит в группу сильно нестехиометрических соединений. В последние два года авторами настоящей работы выполнена серия исследова-ний микроструктуры наноразмерных порошков карбида ниобия [8][9][10][11][12] в зависимости от нестехиометрии, степени гомогенности, малого размера частиц, микродеформа-ций, анизотропии решеточных искажений.…”

Section: Introductionunclassified

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Плотность и размер частиц нанокристаллических порошков кубического карбида ниобия NbC-=SUB=-y-=/SUB=-

Курлов¹,

Гусев²

2017

Физика Твердого Тела

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Методом гелиевой пикнометрии измерена плотность крупнокристаллических (со средним размером частиц 3−5 мкм) и нанокристаллических порошков карбида ниобия NbCy (0.77 ≤ y ≤ 0.96) с разным средним размером частиц от 60 до 30 nm. Нанопорошки получены высокоэнергетическим размолом исходных крупнокристаллических порошков карбида ниобия. Размер частиц в порошках карбида ниобия оценен методами рентгеновской дифракции и Брунауэра−Эммета−Тейлора. Показано, что плотность нанопорошков, измеренная методом гелиевой пикнометрии, занижена по сравнению с истинной плотностью вследствие адсорбции гелия высокоразвитой поверхностью карбидных нанопорошков.

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Ordering of Substoichiometric δ-TiCx Phase in Ti–V–C Alloys

Buršı́k

Weatherly

1999

phys. stat. sol. (a)

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Several Ti–V–C alloys have been studied by transmission electron microscopy (TEM) after cooling from the melt, with special attention paid to ordering processes taking place in the highly substoichiometric (Ti,V)Cx phase. The effects of both short and long range ordering in the carbon sublattice are observed in selected area electron diffraction patterns. The Warren‐Cowley short range order parameters have been evaluated from the intensity distribution in reciprocal space. More complex models for the intensity distribution are then developed and the effects on the predicted short range order parameters are discussed.

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Disorder and Long‐Range Order in Non‐Stoichiometric Interstitial Compounds Transition Metal Carbides, Nitrides, and Oxides

Cited by 142 publications

References 54 publications

Cluster expansion Monte Carlo study of phase stability of vanadium nitrides

Cluster expansion Monte Carlo study of phase stability of vanadium nitrides

Плотность и размер частиц нанокристаллических порошков кубического карбида ниобия NbC-=SUB=-y-=/SUB=-

Ordering of Substoichiometric δ-TiCx Phase in Ti–V–C Alloys

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