scholarly journals Pressure Prediction of Electronic, Anisotropic Elastic, Optical, and Thermal Properties of Quaternary (M2/3Ti1/3)3AlC2(M = Cr, Mo, and Ti)

2016 ◽  
Vol 2016 ◽  
pp. 1-18 ◽  
Author(s):  
Liang Sun ◽  
Yimin Gao ◽  
Yangzhen Liu ◽  
Guoliang Wang ◽  
Yiran Wang ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Ambient Pressure ◽  
Relative Volume ◽  
Ultraviolet Region ◽  
Total Density ◽  
Covalent Bonds ◽  
Optical Functions ◽  
Anisotropic Elastic ◽  
The One ◽  
Total Density Of States

The electronic, mechanical, anisotropic elastic, optical, and thermal properties of quaternary (M2/3Ti1/3)3AlC2(M = Cr, Mo, and Ti) under different pressure are systematically investigated by first-principles calculations. The bonding characteristics of these compounds are the mixture of metallic and covalent bonds. With an increase of pressure, the heights of total density of states (TDOS) for these compounds decrease at Fermi level. The highest volume compressibility among three compounds is Mo2TiAlC2for its smallest relative volume decline. The relative bond lengths are decreasing when the pressure increases. The bulk and shear modulus of the one doped with Cr or Mo are larger than those of Ti3AlC2with pressure increasing. With an increase of pressure, the anisotropy of these compounds also increases. Moreover, Mo2TiAlC2has the biggest anisotropy among the three compounds. The results of optical functions indicate that the reflectivity of the three compounds is high in visible-ultraviolet region up to ~10.5 eV under ambient pressure and increasing constantly when under pressure. Mo2TiAlC2has the highest loss function. The calculated sound velocity and Debye temperature show that they all increase with pressure.CVof the three compounds is also calculated.

Sr3Al2Ge4, Ca10Al6Ge9 und Ca20Al6Ge13. Neue Aluminium-Germanide / Sr3Al2Ge4, Ca10Al6Ge9 and Ca20Al6Ge13. New Aluminium Germanides

2007 ◽  
Vol 62 (8) ◽  
pp. 1071-1082 ◽  
Author(s):  
Marco Wendorff ◽  
Caroline Röhr
Keyword(s):  
Small Deviation ◽  
Multiple Bond ◽  
Ternary Systems ◽  
Monoclinic Space Group ◽  
Band Structure Calculation ◽  
Total Density ◽  
Space Group ◽  
The One ◽  
Total Density Of States ◽  
Bond Character

In the ternary systems Ca-Al-Ge and Sr-Al-Ge three germanides with new structure types have been synthesized from stoichiometric ratios of the elements. Their crystal structures were determined using single crystal X-ray data. In the structure of Sr3Al2Ge4 (monoclinic, space group C2/m, a = 1267.6(4), b = 416.2(2), c = 887.4(3) pm, β = 110.37(2)°, Z = 2, R1 = 0.0354) Al-Ge sheets with Al in tetrahedral (i. e. Al−) and Ge in threefold ψ-tetrahedral (i. e. Ge−) coordination against Ge are present. Thus, the compound can be classified as an electron precise Zintl phase. This finding is verified by the result of a band structure calculation (within the FP-LAPW approach), that shows a distinct minimum of the total density of states at the Fermi level. The structure of Ca10Al6Ge9 (trigonal, space group R3̅m, a = 1398.45(14), c = 2107.4(3) pm, Z = 6, R1 = 0.0613) contains complicated sheets of trigonal planar building units [AlGe3] and [AlGe4] tetrahedra. The compound Ca20[Al3Ge6]2[Ge] (hexagonal, space group P63/m, a = 1600.9(2), c = 458.48(7) pm, Z = 1, R1 = 0.0282) shows two planar trimers of [AlGe3] triangles of formula [Al3Ge6] besides isolated Ge atoms (i. e. Ge4−). The overall electron count of the latter compounds, that contain trigonal planar coordinated Al atoms and considerable multiple bond character of the Al-Ge bonds, shows a very small deviation from the Zintl concept, comparable to the one observed in other aluminium-germanides like SrAlGe.

scholarly journals Theoretical Prediction of CHn Crystal Structures under High Pressures

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1499
Author(s):  
Tao Yang ◽  
Jinjia Liu ◽  
Xiaotong Liu ◽  
Xiulei Liu ◽  
Ning Li
Keyword(s):  
Evolutionary Algorithms ◽  
High Pressures ◽  
Ambient Pressure ◽  
Total Density ◽  
Potential Candidate ◽  
Elevated Pressures ◽  
Graphene Synthesis ◽  
Pressure Region ◽  
Total Density Of States ◽  
High Pressure Region

CHn is the precursor unit for graphene synthesis. We have theoretically predicated a series of CHn structures with n = 1, 2, 4, 6, 8, 10, and 12 at elevated pressures (ambient pressure, 50, 100, 200, 300, 350, and 400 GPa) using evolutionary algorithms. The predicted CH and CH2 structures are graphane-type and polyethylene over the whole considered pressure range, respectively. The molecular crystalline methane is predicted for the stoichiometry of CH4. The combination of methane and H2 for CH6, CH8, CH10, and CH12 up to 300 GPa are obtained. At 400 GPa, the mixture of polymer and H2 for CH6, CH10, and CH12 comes into play. From the computed enthalpy, higher pressure and more hydrogen concentration contributed to the decomposition (to carbon and H2) of CHn systems. The total density of states for these CHn structures show that only the CH12 phase is metallic above 300 GPa. The rotational properties are traced in H2 and the CHn structures. The CH4 rotation is more sensitive to the pressure. The H2 units are nearly freely rotational. Other structures of CHn, including fcc-type and experimentally known structures, are not competitive with the structures predicted by evolutionary algorithms under high pressure region. Our results suggest that the CHn (n > 4) system is a potential candidate for hydrogen storage where H2 could be released by controlling the pressure.

scholarly journals Pressure effect of the mechanical, electronics and thermodynamic properties of Mg–B compounds A first-principles investigations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
GuoWei Zhang ◽  
Chao Xu ◽  
MingJie Wang ◽  
Ying Dong ◽  
FengEr Sun ◽  
...  
Keyword(s):  
Thermodynamic Properties ◽  
First Principles ◽  
Boron Content ◽  
Structural Parameters ◽  
Debye Model ◽  
Total Density ◽  
First Principle ◽  
Volume Deformation ◽  
Temperature And Pressure ◽  
Total Density Of States

AbstractFirst principle calculations were performed to investigate the structural, mechanical, electronic properties, and thermodynamic properties of three binary Mg–B compounds under pressure, by using the first principle method. The results implied that the structural parameters and the mechanical properties of the Mg–B compounds without pressure are well matched with the obtainable theoretically simulated values and experimental data. The obtained pressure–volume and energy–volume revealed that the three Mg–B compounds were mechanically stable, and the volume variation decreases with an increase in the boron content. The shear and volume deformation resistance indicated that the elastic constant Cij and bulk modulus B increased when the pressure increased up to 40 GPa, and that MgB7 had the strongest capacity to resist shear and volume deformation at zero pressure, which indicated the highest hardness. Meanwhile, MgB4 exhibited a ductility transformation behaviour at 30 GPa, and MgB2 and MgB7 displayed a brittle nature under all the considered pressure conditions. The anisotropy of the three Mg–B compounds under pressure were arranged as follows: MgB4 > MgB2 > MgB7. Moreover, the total density of states varied slightly and decreased with an increase in the pressure. The Debye temperature ΘD of the Mg–B compounds gradually increased with an increase in the pressure and the boron content. The temperature and pressure dependence of the heat capacity and the thermal expansion coefficient α were both obtained on the basis of Debye model under increased pressure from 0 to 40 GPa and increased temperatures. This paper brings a convenient understanding of the magnesium–boron alloys.

scholarly journals Experimental and computational study on roles of WOx promoting strong metal support promoter interaction in Pt catalysts during glycerol hydrogenolysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tinnakorn Saelee ◽  
Poonnapa Limsoonthakul ◽  
Phakaorn Aphichoksiri ◽  
Meena Rittiruam ◽  
Mongkol Lerdpongsiripaisarn ◽  
...  
Keyword(s):  
Density Of States ◽  
Design Guidelines ◽  
Total Density ◽  
High Electron ◽  
Metal Support Interaction ◽  
Metal Support ◽  
Glycerol Hydrogenolysis ◽  
The Stability ◽  
Total Density Of States ◽  
Promoter Interaction

AbstractBiodiesel is of high interest due to increased demand for energy with the concern regarding more sustainable production processes. However, an inevitable by-product is glycerol. Hence, the conversion of this by-product to higher-value chemicals, especially 1,3-propanediol (1,3-PDO) via glycerol hydrogenolysis reaction, is one of the most effective pathways towards a profitable process. In general, this process is catalyzed by a highly active Pt-based catalyst supported on γ-Al2O3. However, its low 1,3-PDO selectivity and stability due to surface deactivation of such catalysts remained. This led to the surface modification by WOx to improve both the selectivity by means of the increased Brønsted acidity and the stability in terms of Pt leaching-resistance. Hence, we applied experimental and density functional theory (DFT)-based techniques to study the fundamentals of how WOx modified the catalytic performance in the Pt/γ-Al2O3 catalyst and provided design guidelines. The effects of WOx promoter on improved activity were due to the shifting of the total density of states towards the antibonding region evident by the total density of states (TDOS) profile. On the improved 1,3-PDO selectivity, the main reason was the increasing number of Brønsted acid sites due to the added WOx promoter. Interestingly, the stability improvement was due to the strong metal-support interaction (SMSI) that occurred in the catalyst, like typical high leaching-resistant catalysts. Also, the observed strong metal-support-promoter interaction (SMSPI) is an additional effect preventing leaching. The SMSPI stemmed from additional bonding between the WOx species and the Pt active site, which significantly strengthened Pt adsorption to support and a high electron transfer from both Pt and Al2O3 to WOx promoter. This suggested that the promising promoter for our reaction performed in the liquid phase would improve the stability if SMSI occurred, where the special case of the WOx promoter would even highly improve the stability through SMSPI. Nevertheless, various promoters that can promote SMSPI need investigations.

scholarly journals THE PHONON SPECTRUM OF THE OCTAGONAL TILING

1993 ◽  
Vol 07 (06n07) ◽  
pp. 1505-1525 ◽  
Author(s):  
J. LOS ◽  
T. JANSSEN ◽  
F. GÄHLER
Keyword(s):  
Specific Heat ◽  
Density Of States ◽  
Phonon Spectrum ◽  
Low Frequency ◽  
Debye Model ◽  
Square Lattice ◽  
Total Density ◽  
Unit Cells ◽  
Linear Behaviour ◽  
Total Density Of States

A study of the phonon spectrum of the octagonal tiling is presented, by calculating and analysing the properties of the spectrum of perfect and randomized commensurate approximants with unit cells containing up to 8119 vertices. The total density of states, obtained by numerical integration over the Brillouin zone, exhibits much structure, and in the low frequency range of the spectrum there is deviation from the normal linear behaviour in the form of pseudogaps. For randomized approximants these pseudogaps disappear and the density of states is globally smoothened. It turns out that the widths of the gaps in the dispersion vanish in the low frequency limit. Therefore the scaling behaviour of the lowest branches tends to the behaviour of an absolutely continuous spectrum, which is not the case at higher frequencies. As an application, the vibrational specific heat of the different tiling models is calculated and compared to the specific heat of a square lattice and of a Debye model.

scholarly journals Numerical and Experimental Investigations of Coupling Effects in Anisotropic Elastic Rotors

1999 ◽  
Vol 5 (4) ◽  
pp. 263-271 ◽  
Author(s):  
Horst Irretier ◽  
Georges Jacquet-Richardet ◽  
Frank Reuter
Keyword(s):  
Coupling Effect ◽  
Experimental Results ◽  
Mode Shapes ◽  
Experimental Investigations ◽  
Coupling Effects ◽  
Symmetry Approach ◽  
Anisotropic Elastic ◽  
Elastic Modes ◽  
Bending Modes ◽  
The One

It is known that in elastic disc-shaft systems in particular, the one-nodal-diameter mode of the discs can be highly coupled with the bending modes of the shaft. Consequently, when the system rotates, the elastic modes of the flexible discs are coupled with the gyroscopic modes of the flexible shaft equipped with rigid discs. In the paper this coupling effect is investigated numerically and experimentally.A numerical model, based on a finite element cyclic symmetry approach, is presented. This model has been developed for studying the wheel-shaft coupling effects on the global behavior of turbomachinery rotors. In order to better illustrate the phenomenon involved and to validate the model, the method is applied here to a thin tuned and detuned circular disc mounted on an elastic shaft. Related frequency and mode shapes of the rotating assembly are discussed. Additional experimental results, based on an experimental modal analysis technique for rotating structures, are presented. Both numerical and experimental results are compared.

Tailoring thermal properties of ambient pressure dried MTMS/TEOS co-precursor aerogels

2016 ◽  
Vol 171 ◽  
pp. 91-94 ◽  
Author(s):  
Zhi Li ◽  
Xudong Cheng ◽  
Song He ◽  
Xiaojing Shi ◽  
Hui Yang ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Ambient Pressure

scholarly journals Preparation of a Novel Epoxy/SiO2 Hybrid Coating

2005 ◽  
Vol 14 (1) ◽  
pp. 096369350501400 ◽  
Author(s):  
C. H. Zhang ◽  
Y. P. Bai ◽  
L. X. Liu ◽  
Z. Q. Zhang ◽  
Q. Y. Li
Keyword(s):  
Thermal Properties ◽  
Epoxy Resin ◽  
Sol Gel ◽  
Covalent Bond ◽  
Decomposition Temperature ◽  
Hybrid Coating ◽  
Epoxy Coating ◽  
Covalent Bonds ◽  
Surface Image ◽  
Gel Technique

In this paper, epoxy/SiO2 hybrid coating was successfully prepared through sol-gel technique, the structure and thermal properties of epoxy/SiO2hybrid coating were investigated. First, γ-isocyanatopropyltriethoxysilane “(KBE-9007)” was used to modify the epoxy resin so that the ethoxysilane could be grafted on the epoxy resin. Nano-SiO2 precursor was synthesized by tetraethoxysilane(TEOS) through sol-gel technique. Then the modified epoxy resin and the nano-SiO2 precursor were mixed for 4 hours to let the macromolecules of epoxy resin graft on the surface of nano-SiO2, and modified nano-SiO2 precursor was obtained. At last, epoxy/SiO2 hybrid coating was produced by using the modified nano-SiO2 precursor. The graft reaction was confirmed by the analyses of FT-IR. The analyses of XPS indicated that there are lots of SiO2 particles and Si-C covalent bonds on the surface of epoxy/SiO2 hybrid coating, they also suggested that most TEOS had changed into SiO2 particles and Si-C covalent bond had been formed between epoxy resin and SiO2. The analyses of SEM fracture surface image of epoxy/SiO2 hybrid coating showed that SiO2 particles dispersed in epoxy matrix homogeneously and the size of the particles was between 50nm and 100 nm. Thermoanalysis Instrument was employed to detect the thermal properties of epoxy coating and epoxy/SiO2 hybrid coating, the results indicated that the thermal decomposition temperature of epoxy/SiO2 hybrid coating is 21.7 °C higher than that of epoxy coating, the thermal properties of the epoxy/SiO2 hybrid coating were improved because of the introduction of nano-SiO2.

scholarly journals Ab-initio study of the orthorhombic ndmno3 perovskite

2014 ◽  
Vol 70 (a1) ◽  
pp. C1806-C1806
Author(s):  
Samir Bentata ◽  
Bouabdellah Bouadjemi ◽  
Tayeb Lantri ◽  
Wissem Benstaali
Keyword(s):  
Density Functional ◽  
Electronic Band Structure ◽  
Total Density ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Functional Theory ◽  
Half Metallic ◽  
Generalized Gradient Approximation ◽  
Ferromagnetic Ground State ◽  
Total Density Of States

We investigate the structural, electronic and magnetic properties of the orthorhombic Perovskite oxyde NdMnO3 through density-functional-theory (DFT) calculations using both generalized gradient approximation GGA+U, where U is on-site Coulomb interaction correction. The electronic band structure, the partial and total density of states (DOS) and the magnetic moment are determined. The results show a half-metallic ferromagnetic ground state for the orthorhombic NdMnO3.

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