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1.
Yong Pan 《International journal of quantum chemistry》2019,119(15):e25943
Cr-Al binary compounds are regarded as the potential high-temperature structural materials. However, the structure and important properties of Cr-Al compounds are not completely unclear. Here, we report on the influence of Cr concentration on the structural, mechanical, and thermodynamic properties of Cr-Al compounds by using the first-principles calculations. Four novel Cr-Al compounds, Cr3Al8 with monoclinic structure (C2/m), Cr3Al5 with hexagonal structure (P63mc), Cr2Al3 with tetragonal structure (I4/mmm), and Cr3Al with cubic structure (Pm-3 m), are predicted. The calculated elastic modulus of Cr-Al compounds gradually increases with increasing Cr concentration. Compared to other Cr-Al compounds, our predicted Cr3Al with cubic structure exhibits a strong deformation resistance and high hardness due to symmetrical Cr Al bonds. However, the Debye temperature of Cr7Al3 is larger than that of other Cr-Al compounds. The calculated phonon density of state shows that the high-temperature thermodynamic properties of Cr-Al compounds are attributed to the vibration of Al atom and Cr Al bond. 相似文献
2.
Cheng‐Ho Chen Chih‐Chun Teng Shun‐Fua Su Wen‐Chang Wu Chien‐Hsin Yang 《Journal of Polymer Science.Polymer Physics》2006,44(2):451-460
A Haake torque rheometer equipped with an internal mixer has been used to study the influence of microscale calcium carbonate (micro‐CaCO3) and nanoscale calcium carbonate (nano‐CaCO3) on the fusion, thermal, and mechanical characteristics of rigid poly(vinyl chloride) (PVC)/micro‐CaCO3 and PVC/nano‐CaCO3 composites, respectively. The fusion characteristics discussed in this article include the fusion time, fusion temperature, fusion torque, and fusion percolation threshold (FPT). The fusion time, fusion temperature, and FPT of rigid PVC/calcium carbonate (CaCO3) composites increase with an increase in the addition of micro‐CaCO3 or nano‐CaCO3. In contrast, the fusion torque of rigid PVC/CaCO3 composites decreases with an increase in the addition of micro‐CaCO3 or nano‐CaCO3. The results of thermal analysis show that the first thermal degradation onset temperature (Tonset) of rigid PVC/micro‐CaCO3 is 7.5 °C lower than that of PVC. Meanwhile, the glass‐transition temperature (Tg) of rigid PVC/micro‐CaCO3 is similar to that of PVC. However, Tonset and Tg of PVC/nano‐CaCO3 composites can be increased by up to 30 and 4.4%, respectively, via blending with 10 phr nano‐CaCO3. Mechanical testing results for PVC/micro‐CaCO3 composites with the addition of 5–15 phr micro‐CaCO3 and PVC/nano‐CaCO3 composites with the addition of 5–20 phr nano‐CaCO3 are better than those of PVC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 451–460, 2006 相似文献
3.
Although ZrB12 is a promising advanced material because of the boron cuboctahedron cages, the hardness of ZrB12 remains controversy. Here, we apply first-principles calculations to study the influence of transition metals (4d- and 5d-) on the hardness and thermodynamic properties of ZrB12. The calculated hardness of ZrB12 is 32.9 GPa, which is in good agreement with the previous theoretical result. Importantly, the calculated hardness of Re-doped ZrB12 is up to 40.0 GPa, which is a potential superhard material. The essential reason is that the alloying element of Re enhances the localized hybridization of B B and Zr B atoms, and then forms the strong B B covalent bond and Zr B bond. The result is well demonstrated by the chemical bonding and lattice parameter. Here, our work shows that the alloying elements of Nb, Mo, and Re enhance the thermodynamic properties of ZrB12. The Debye temperature of Re-doped ZrB12 is 1225.2 K, which is larger than that of the parent ZrB12 (1213.5 K). 相似文献
4.
The B2-type cubic Zr-based compounds are attractive advanced high-temperature materials because of the strong and symmetrical bonds. However, the mechanical and thermodynamic properties of the B2-type cubic Zr-based compounds are not well understood. Here, we use the first-principles calculations to investigate the structural, elastic modulus, ductility, and thermodynamic properties of TMZr (TM = Ru, Mo, Rh, Os, and Re) compounds. Two novel TMZr compounds, MoZr and ReZr, are first predicted by using the phonon dispersion and formation enthalpy, respectively. The results show that the B2-type TMZr compounds not only exhibit high elastic modulus but also show better ductility due to the symmetrical TM-Zr metallic bonds. In particular, the calculated elastic modulus of OsZr is larger than that of the other four TMZr compounds, indicating that the OsZr shows the strongest deformation resistance in five TMZr compounds. The calculated Θ D of RuZr is 328 K, which is larger than that of the other four TMZr compounds. The calculated phonon density of state shows that the high-temperature thermodynamic properties of TMZr derive from the vibration of Zr atom. Therefore, our work predicts that the B2-type OsZr is an attractive high-temperature structural material. 相似文献
5.
Yong Pan 《International journal of quantum chemistry》2020,120(22):e26401
Although CrSi2 silicide is an attractive advanced functional material, the improvement of electronic and optical properties is still a challenge for its applications. Here, we apply the first-principles calculations to investigate the influence of transition metals (TMs) on the electronic and optical properties of C40 CrSi2 silicide. Five possible TMs, Ti, V, Pd, Ag, and Pt, are considered in detail. The calculated results show that the additive metals Ti, V, Pd, and Pt are thermodynamically stable in C40 CrSi2 because the calculated impurity formation energy of TM-doped C40 CrSi2 is lower than zero. In particular, the V dopant is more thermodynamically stable than that of the other TMs. The calculated electronic structure shows that the band gap of C40 CrSi2 is 0.391 eV, which is in good agreement with the other results. In particular, the additive TMs improve the electronic properties of C40 CrSi2 due to the role of the d-state of TMs. Naturally, the additive TMs result in band migration (Cr-3d state and Si-3p state) from the valence band to the conduction band. Interestingly, the additive TMs lead to a red shift for optical adsorption of C40 CrSi2 silicide. 相似文献
6.
Kan Luo Xian-Hu Zha Yuhong Zhou Qing Huang Shenghu Zhou Shiyu Du 《International journal of quantum chemistry》2020,120(24):e26409
MXenes have attracted intensive attention in chemistry and material science for their special structures and properties. In order to understand the basic physical properties of the M3C2/M3C2T2 (MSc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W; TF, O, OH) MXenes, first-principles calculations are carried out to investigate the structural, vibrational, and mechanical properties in this work. Both the metal atoms and surface groups can significantly influence the configurations or mechanical behaviors of the MXenes. The dehydrogenation tendency is calculated to evaluate the possible forms of the M3C2(OH)2 toward M3C2O2. The work functions of MXenes functionalized by different groups are compared, and the lower work functions for the OH functionalized ones, which can be as low as 1.358 eV for the Sc3C2(OH)2, suggest potential good performance in electron emission. In addition, the stability, mechanical properties, and the Raman and infrared (IR) activity modes of the MXenes are reported. Generally, functionalized MXenes would present smaller lattice parameters, lower free energies, and stronger mechanical strength compared to their counterparts. The data obtained may provide important theoretical ground for the investigations of the applications of MXenes. 相似文献
7.
We apply the first-principles approach to study the structural stability, Vickers hardness, and elastic modulus of ReB12 and RuB12. In particular, we further investigate the influence of high pressure on the structural stability and mechanical properties of ReB12 and RuB12. The calculated results show that ReB12 and RuB12 are thermodynamic stability under high pressure. Here, ReB12 is more thermodynamic stability than that of the RuB12. The calculated Vickers hardness of ReB12 and RuB12 is 16.25 and 16.55 GPa, respectively. It is found that the calculated elastic constants and elastic modulus of ReB12 and RuB12 increase with increasing pressure. In particular, the calculated elastic constants and elastic modulus of ReB12 are larger than that of the RuB12. The calculated electronic structure shows that the high hardness and elastic modulus of ReB12 and RuB12 are attributed to the 3D network B-B covalent bonds. 相似文献
8.
为了探索AlN在光电器件中的潜在应用,采用第一性原理计算了不同Lu掺杂浓度(以原子分数x表示)的AlN(Al1-xLuxN)的电子结构和光学性质。研究结果表明,Al1-xLuxN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al1-xLuxN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al1-xLuxN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al1-xLuxN的光电导率在低能区随能量的增加而急剧增加。 相似文献
9.
为了探索 AlN在光电器件中的潜在应用,采用第一性原理计算了不同 Lu掺杂浓度(以原子分数 x表示)的 AlN(Al1-xLuxN)的电子结构和光学性质。研究结果表明,Al1-xLuxN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al1-xLuxN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al1-xLuxN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al1-xLuxN的光电导率在低能区随能量的增加而急剧增加。 相似文献
10.
PBS/nano-CaCO3 composites with various nano-CaCO3 weight fractions were prepared by melt blending. The thermal behavior, dynamic mechanical properties and rheological properties of the composites were investigated. DSC measurements revealed that the nano-CaCO3 particles had little influence on the crystallization and melting behavior of PBS. Thermogravimetric analysis showed that the introduction of nano-CaCO3 tended to improve the thermal stability of PBS. Dynamic mechanical analysis showed that the G′ and G″ of the PBS/nano-CaCO3 composites were improved significantly when the nano-CaCO3 content was not more than 3wt%, while the G′ and G″ were mainly decided by the PBS matrix when the nano-CaCO3 content exceeded 3wt%. Rheological results showed that G′ < G″ over the frequency range, illustrating the viscous behavior of the samples. The η* of all the samples remained almost constant when the frequency was not more than 0.25 rad/s, which showed the characteristic of a Newtonian fluid. A strong shear thinning effect was observed for all the samples when the frequency exceeded 0.25 rad/s. Furthermore, the microstructure and the relaxation mechanism of the PBS/nano-CaCO3 composites mainly depended on the PBS matrix. 相似文献
11.
A theoretical study of structural, electronic and optical properties of Ag2S is presented using the full potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the modified Becke Johnson (MBJ) potential coupled with Local Density Approximation (LDA) was used for the exchange-correlation potential calculation. Ground state properties are determined for the bulk material in monoclinic phase. Band structure reveals that this compound is a direct energy band gap semiconductor. MBJLDA results for the band gap of this compound are much better than those obtained using LDA, Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and Engel–Vosko's GGA (EV-GGA). A very good agreement is observed between MBJLDA band gap and corresponding experimental values as compared to other calculations. Optical constants including the dielectric function, refractive index, extinction coefficient, electron energy loss function, reflectivity and absorption coefficient are obtained and discussed. 相似文献
12.
The structural and mechanical properties of alkali hydrides (LiH, NaH, KH, RbH, and CsH) were investigated via first-principles calculations which cover the optimized structural parameters. The density functional theory in combination with the generalized gradient approximation (GGA) were used in this study. From the present study, one could note that alkali hydrides are brittle materials and mechanically stable. It was found that stiffness and shear resistance are greater in LiH than in other hydrides. It is more brittle in nature, and comparatively harder than the other materials under study; it also presents a high degree of anisotropy. The results were then investigated and analyzed with principal component analysis (PCA), which is one of the most common techniques in multivariate analysis, was used to explore the correlations among material properties of alkali hydrides and to study their trends. The alkali hydrides obtained by the first-principles calculations were also compared with the alkaline-earth metal hydrides (BeH2, MgH2, CaH2, SrH2, and BaH2) and discussed in this work. 相似文献
13.
Summary Thermal and dynamic mechanical properties of carbon dioxide and propylene oxide alternative copolymer, poly(propylene carbonate)
(PPC), and the end-capped PPC with maleic anhydride were investigated by means of TG and DMA. A master curve of the storage
modulus vs. frequency can be deduced from the isochronal curves. Physical parameters of both plain and MA end-capped PPC were discussed.
The results showed that for maleic anhydride (MA) end-capping PPC, an improvement of its thermal stability and mechanical
properties accompanied with some modifications of the viscoelastic behavior were obtained. 相似文献
14.
Anchoring calcium carbonate on graphene oxide reinforced with anticorrosive properties of composite epoxy coatings
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Haihui Di Zongxue Yu Yu Ma Yang Pan Heng Shi Liang Lv Fei Li Chun Wang Ting Long Yi He 《先进技术聚合物》2016,27(7):915-921
Calcium carbonate nanoparticles (nano‐CaCO3) anchored graphene oxide (GO) sheet nanohybrids (GO‐CaCO3) are fabricated, and their structure can be measured by scanning electron microscope, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction and Fourier‐transform infrared spectroscopy analysis. Afterwards, composite epoxy coatings, filled with GO and GO‐CaCO3 nanohybrids, are prepared via a curing process. The dispersion and anticorrosive properties of composite epoxy coatings are investigated. The results reveal that GO‐CaCO3 nanohybrids achieve a homogeneous dispersion as well as reinforce corrosion resistance of epoxy coatings. Furthermore, the anticorrosive mechanisms are tentatively proposed for the GO‐CaCO3/epoxy coatings. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
15.
Diyou Jiang Shuying Zhong Wenbo Xiao Desheng Liu Musheng Wu Sanqiu Liu 《International journal of quantum chemistry》2020,120(13):e26231
The structural, mechanical, electronic, and thermodynamic properties of pure W metal under different pressures have been investigated using the first-principles method. Our calculated structural parameters are in good agreement with experimental and previous theoretical results. The obtained elastic constants show that pure W metal is mechanically stable. Elastic properties such as the bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (ν), Cauchy pressure (C′), and anisotropy coefficients (A) are calculated by the Voigt-Reuss-Hill method. The results show that the pressure can improve the strength of pure tungsten and has little effect on the ductility. In addition, the total density of states as a function of pressure is analyzed. Thermodynamic properties such as the Debye temperature, phonon dispersion spectrum, free energy, entropy, enthalpy, and heat capacity are also discussed. 相似文献
16.
<正>The effect ofαphase nucleating agent(NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol(DMDBS) on crystallization and physical properties of polypropylene/calcium carbonate(PP/CaCO_3) composites has been comparatively investigated.Compared with binary PP/CaCO_3 composites,in which CaCO_3 exhibits weak heterogeneous nucleation, inconspicuous reinforcement and toughening effects for PP,the introduction of a few amounts of DMDBS induces a great increase of the degree of crystallinity.Largely improved tensile properties,fracture toughness at relatively higher temperature and heat deformation temperature(HDT) are observed for DMDBS nucleated PP/CaCO_3 composites. 相似文献
17.
Karagiannis EE Kefalidis CE Petrakopoulou I Tsipis CA 《Journal of computational chemistry》2011,32(7):1241-1261
The structural, electronic, bonding, magnetic, and optical properties of bimetallic [Cu(n)Ru(m)](+/0/-) (n + m ≤ 3; n, m = 0-3) clusters were computed in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) using the full-range PBE0 nonlocal hybrid GGA functional combined with the Def2-QZVPP basis sets. Several low-lying states have been investigated and the stability of the ground state spinomers was estimated with respect to all possible fragmentation schemes. Molecular orbital and population analysis schemes along with computed electronic parameters illustrated the details of the bonding mechanisms in the [Cu(n Ru(m)](+/0/-) clusters. The TD-DFT computed UV-visible absorption spectra of the bimetallic clusters have been fully analyzed and assignments of all principal electronic transitions were made and interpreted in terms of contribution from specific molecular orbital excitations. 相似文献
18.
Structures of transition metal nitrides (TMNs) were optimized using the plane-wave pseudopotential method based on density functional theory. Energy as a function of volume curves were calculated to predict the phase transition pressures. Density of states (DOS), charge density difference, and charge transfers were calculated. The elastic constant (C11) and modulus (G) as a function of pressure were computed. Results showed that TMNs in the WC structure was most stable at normal pressure. All TMNs exhibited metallic, covalent and ionic property. Metallic character increased and covalent property reduced with increasing atomic number of TM atom. The elastic constant (C11) and modulus (G) increased linearly with increasing pressure due to stronger hybridization, bonding and covalent property. Thus, mechanical property enhanced under external pressure. 相似文献
19.
Ternary chalcogenides with direct band gaps are remarkable for being used in many optoelectronic applications. We investigated for structural, electronic, optical, and transport characteristics of new Ba2CdCh3 (Ch = S, Se, Te) semiconductors using the full-potential linearized augmented plane wave (FP-LAPW) approach. The band structures of these compounds confirm a direct type of band gap. The phonon dispersion plots along with the predicted negative formation energies suggest these compounds to be thermodynamically stable. Additionally, important optical characteristics were computed and thoroughly explained. The different ELF spectra were calculated in which strong peak correlate precisely with plasma resonance. Moreover, we also explored the thermodynamic characteristics of the ternary systems by employing the quasi-harmonic Debye model. These compounds were also suitable for thermoelectric applications based on the detailed discussion of the computed significant thermoelectric properties. In general, the advancement of various and promising semiconducting devices and their applications will be supported by the present study. 相似文献
20.
The electronic and optical natures of silica-coated semiconductor nanocrystals (Cd(2)Te(2)@(SiO(2))(24)) have been investigated by density functional theory (DFT) and time-dependent DFT calculations. The calculated results of Cd(2)Te(2)@(SiO(2))(24) have revealed that the structural synergy effect between the Cd(2)Te(2) quantum dots (QDs) and the silica coating shell plays a dominant role in the photoelectric properties. The binding of embedded Cd(2)Te(2) to the outer silica coating shell leads to the distortion of the silica nanocage, indicating strong coupling between the QDs and silica shell. The optical features of Cd(2)Te(2) clusters and Cd(2)Te(2)@(SiO(2))(24) complexes were evaluated using the time-dependent DFT method. It is determined that the maximal absorption peak of isolated Cd(2)Te(2) in a UV-Vis absorption spectrum appears at 584 nm, which shifts to 534 nm when the Cd(2)Te(2) QDs were encapsulated by silica, in close agreement with the experimental evidence. The excited process has a direct electronic transition character from the occupied Cd(2)Te(2) states to the outer silica nanocage excited states (core → shell electronic transitions). A deep insight into silica-coated QD systems is beneficial for understanding their optical nature and the development of core/shell QDs. 相似文献