Thermodynamic and kinetic aspects of decomposition of MgB2 in vacuum: Implications for optimization of synthesis conditions

Brutti, Sergio; Balducci, G.; Gigli, G.; Ciccioli, A.; Manfrinetti, P.; Palenzona, A.

doi:10.1016/j.jcrysgro.2005.12.105

Cited by 26 publications

(15 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Among these compounds, magnesium diboride is a very promising material due to its relatively high Curie temperature (∼40 K), simple structure, low anisotropy and high coherence lengths. [1,2] In addition to MgB 2 , characterized by a honeycomb structure very similar to graphite, [3,4] other thermodynamically stable borides, MgB x (with x = 4, 7, 12 and 20), have also been observed previously. [5,6] Owing to a high value of coherence length, during the synthesis of MgB 2 , it is possible to obtain excellent superconductors in a wide range of compound's crystallinity and with not very pronounced dependence on the grains' size.…”

Section: Introductionmentioning

confidence: 62%

Chemical composition of magnesium boride films obtained by CVD

Crociani

Carta

Kačiulis

et al. 2008

Surface & Interface Analysis

View full text Add to dashboard Cite

The films of magnesium boride were grown on Si(100) substrate by chemical vapor deposition, starting from the synthesis of the single-source precursor Mg(BH 4 ) 2 . The deposition time was varied to study its influence on the film composition. The chemical composition of produced samples was investigated by the XPS technique. The depth profiling of MgB x films was carried out by using Ar ion sputtering combined with cyclic XPS measurements. The contributions of different chemical species (boride and oxides) in the depth profiles were separated by peak-fitting analysis of photoelectron B 1s and Auger Mg KLL spectra. In order to determine the correct parameters of peak fitting, the reference samples of MgB 2 and MgO were studied as well. The produced samples were composed of MgB x film covered by an overlayer of magnesium and boron oxides, whose thickness was increasing with deposition time. The surface of the films was enriched with magnesium, while the volume was characterized by the B : Mg ratio exceeding 2. XPS results confirmed that the bulk decomposition of Mg(BH 4 ) 2 precursor was successful; therefore, some other phenomenon, such as Mg segregation, was responsible for the formation of MgB x films with x > 2. In addition, a prolonged deposition time resulted in a thicker surface overlayer of Mg and B oxides, but it did not change the stoichiometry of the boride film.

show abstract

Section: Introductionmentioning

confidence: 62%

Chemical composition of magnesium boride films obtained by CVD

Crociani

Carta

Kačiulis

et al. 2008

Surface & Interface Analysis

View full text Add to dashboard Cite

show abstract

“…We chose MgB 2 , a well-known compound with unexpected superconducting capabilities, [21][22][23] as its Mg partial pressure had been examined in detail and amounts to not more than 10 À3 mbar at 800 8C. [24][25][26][27] In principle, the following reactions to produce MgCl 2 The subtraction of Equation (2) from Equation (1) yields the relevant components for the equilibrium presented in Equation (3). Finally, supported by several experiments on the thermal stability of MgB 2 [24][25][26]30] as well as by quantum-chemical calculations on MgCl and Mg 2 Cl 2 , the temperature-dependent partial pressure curves of MgCl 2 , MgCl, and Mg 2 Cl 2 are obtained ( Figure 1).…”

Section: Ch]mentioning

confidence: 99%

MgCl and Mg₂Cl₂: From Theoretical and Thermodynamic Considerations to Spectroscopy and Chemistry of Species with MgMg Bonds

2008

View full text Add to dashboard Cite

Recently, compounds containing metal-metal bonds between main-group elements have attracted interest to a surprising extent. [1][2][3][4][5] In spite of the latest structural results for two crystalline Mg 2 R 2 compounds (R1 = [ArNC(NiPr 2 )NAr] À ; R2 = [{ArNCMe} 2 CH] À ; Ar= 2,6-diisopropylphenyl, iPr = isopropyl) [2] and in spite of a number of theoretical contributions on molecules with MgÀMg bonds, [10][11][12] several important questions still remain to be answered, for example, concerning the unexpected disproportionation stability of the abovementioned Mg I compounds. Herein, we present the following results: 1) On the basis of quantum-chemical-assisted thermodynamic calculations, a feasible synthesis of radical monomeric Mg I halides at temperatures near 900 8C is presented.2) The nature of the MgÀMg bond is investigated by spectroscopic examination of MgCl and its linear dimer Mg 2 Cl 2 in solid inert-gas matrixes; the MgÀMg dissociation energy is obtained. 3) By comparing the thermodynamics of Mg 2 Cl 2 (1), Mg 2 Cp 2 (2, Cp = cyclopentadienyl), and a model compound Mg 2 R* 2 (3, R* = C(NH 2 )(NCH 3 ) 2 ) analogous to crystalline Mg 2 (R1) 2 , the enormous disproportionation stability of the latter compound is explained. For further investigations, for example in the field of metal-rich Mg n R m clusters (n > m), the synthesis of reactive starting materials like MgCl is absolutely necessary. Initial results on the synthesis of MgCl are reported.After the first evidence for stable alkaline earth

show abstract

“…In air, the MgB 2 starts to decompose into MgB 4 at temperatures higher than 850°–950°C 7 . Several groups 8,9 studied the vaporization under a vacuum of MgB 2 , indicating that the decomposition temperature of MgB 2 decreases with decreasing vacuum conditions.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Phase Transformation Between MgB₂ and MgB₄

Yan

Guo

Liu

et al. 2007

Journal of the American Ceramic Society

View full text Add to dashboard Cite

Using X‐ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), we have investigated the reaction between MgB4 and Mg in its solid, liquid, and gas physical states. The XRD results indicate that the reaction of MgB4+Mg=2MgB2 always occurs independently of the different states of Mg. DSC measurements show that the solid–solid reaction MgB4(s)+Mg(s)=2MgB2(s), the Mg melting Mg(s)→Mg(l), and the Mg volatilization occur in turn with increasing temperature for mixed (MgB4+Mg) powder with a nominal stoichiometry of MgB2. SEM observations indicate that the resulting synthesized MgB2 samples, obtained from the MgB4+Mg mixtures, have a denser microstructure than those obtained directly from Mg+B mixtures. On the basis of XRD, DSC, and SEM results, a kinetic model for the reaction between MgB4 and Mg is proposed.

show abstract

Thermodynamic and kinetic aspects of decomposition of MgB2 in vacuum: Implications for optimization of synthesis conditions

Cited by 26 publications

References 21 publications

Chemical composition of magnesium boride films obtained by CVD

Chemical composition of magnesium boride films obtained by CVD

MgCl and Mg₂Cl₂: From Theoretical and Thermodynamic Considerations to Spectroscopy and Chemistry of Species with MgMg Bonds

Experimental Study on Phase Transformation Between MgB₂ and MgB₄

Contact Info

Product

Resources

About

Thermodynamic and kinetic aspects of decomposition of MgB2 in vacuum: Implications for optimization of synthesis conditions

Cited by 26 publications

References 21 publications

Chemical composition of magnesium boride films obtained by CVD

Chemical composition of magnesium boride films obtained by CVD

MgCl and Mg2Cl2: From Theoretical and Thermodynamic Considerations to Spectroscopy and Chemistry of Species with MgMg Bonds

Experimental Study on Phase Transformation Between MgB2 and MgB4

Contact Info

Product

Resources

About

MgCl and Mg₂Cl₂: From Theoretical and Thermodynamic Considerations to Spectroscopy and Chemistry of Species with MgMg Bonds

Experimental Study on Phase Transformation Between MgB₂ and MgB₄