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81.
The Pr1−xPbxMnO3 (x=0.1–0.5) perovskites have been fabricated by solid-state reaction. The X-ray diffraction patterns show that the samples are of single phase with orthorhombic structure. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic curves measured at low field and low temperatures exhibit the spin glass-like state. The Curie temperature of samples increased with increase in Pb content. The maximum magnetic entropy change |ΔSm|max reaches the giant values of 3.91 and 3.68 J/kg K for quite low magnetic field change of 1.35 T for the samples x=0.1 and 0.4, respectively. The resistance measurements show that there is insulator–metal phase transition on the R(T) curves for samples with x?0.3. The giant magnetoresistance effect is also observed for all samples studied. 相似文献
82.
Thuy Trang NguyenThanh Cong Bach Huong Thao PhamThe Tan Pham Duc Tho NguyenNam Nhat Hoang 《Physica B: Condensed Matter》2011,406(19):3613-3621
The electronic structures of bulk, 2D slabs and clusters of CaMnO3 in various magnetic configurations are presented. The obtained results including optimized cell constant, band-gap, Mn magnetic moment, on-site Coulomb repulsion potential and p-d charge separation potential are in good agreement with experiment data. The energetically most preferable configuration was an insulating charge-transfer ground state with G-type antiferromagnetic (AF) configuration (classified according to Wollan and Koehler, Phys. Rev. 100 (1955) 545). For the finite 2D layers the C-type AF ground state was found to be most stable. The surface effect on magnetism of finite quasi 2D systems appeared to originate in the pyramidal field splitting of Mn 3d levels, which induced the formation of ferromagnetic (FM) regions within the AF matrix and the extension of FM correlation deep through 7 subsurface layers (2.7 nm from the surface). All finite systems (clusters and slabs) were found non-conducting due to the localization of electrons and the cancellation of surface excess carriers (holes) after surface relaxation, although the band-gaps of 2D systems were sufficiently reduced in comparison with that of the bulk. 相似文献
83.
The thickness effects on the microstructure and soft magnetic properties of CoFeHfO thin films have been investigated in the range of 100–600 nm. There was a significant change in the coercivity (Hc) and the anisotropy (Hk) value with increasing film thickness, but the saturation induction and the resistivity almost remain unchanged. Hc and Hk reached a minimum value of 0.19 Oe and a maximum value of 50 Oe, respectively at 200 nm film thickness. The high saturation magnetic induction is 21 kG and resistivity is 500 μΩ cm. The origin of the changing Hc and Hk values is discussed in detail based on change of microstructure along with film thickness. 相似文献
84.
85.
Chien H. Thai Loc V. Tran Dung T. Tran T. Nguyen-Thoi H. Nguyen-Xuan 《Applied Mathematical Modelling》2012
This paper presents a novel finite element formulation for static, free vibration and buckling analyses of laminated composite plates. The idea relies on a combination of node-based smoothing discrete shear gap method with the higher-order shear deformation plate theory (HSDT) to give a so-called NS-DSG3 element. The higher-order shear deformation plate theory (HSDT) is introduced in the present method to remove the shear correction factors and improve the accuracy of transverse shear stresses. The formulation uses only linear approximations and its implementation into finite element programs is quite simple and efficient. The numerical examples demonstrated that the present element is free of shear locking and shows high reliability and accuracy compared to other published solutions in the literature. 相似文献
86.
Thron JL Allison WW Alner GJ Ambats I Ayres DS Balka LJ Barr GD Barrett WL Benjamin D Border PM Brooks CB Cobb JH Cockerill DJ Courant H Dawson JW Demuth DM Edwards VW Ewen B Fields TH Garcia-Garcia C Giles RH Giller GL Goodman MC Gray RN Heilig SJ Hill N Hoftiezer JH Jankowski DJ Johns K Kafka T Kasahara SM Kochocki J Leeson W Litchfield PJ Longley NP Lopez FV Lowe MJ Mann WA Marshak ML May EN Maxam D McMaster L Milburn RH Miller WH Minor CP Napier A Oliver WP Pearce GF Perkins DH Peterson EA 《Physical review D: Particles and fields》1992,46(11):4846-4851
87.
Dr. Jules Tshishimbi Muya Dr. Erwin Lijnen Prof. Dr. Minh Tho Nguyen Prof. Dr. Arnout Ceulemans 《Chemphyschem》2013,14(2):346-363
Extensive optimisation calculations are performed for the B80 isomers in order to find out which principles underlie the formation of large hollow boron cages. Our analysis shows that the most stable isomers contain triangular B10 or rhombohedral B16 building blocks. The lowest‐energy isomer has C3v symmetry and is characterised by a belt of three interconnected B16 units and two separate B10 units. At the B3LYP/6‐31G(d) level of theory, this newly discovered isomer is 2.29, 1.48, and 0.54 eV below the leapfrog B80 of Szwacki et al., the Th‐B80 of Wang, and the D3d‐B80 of Pochet et al., respectively. Our C3v isomer is therefore identified as the most stable hollow cage isomer of B80 presently known. Its HOMO–LUMO gap of 1.6 eV approaches that of the leapfrog B80. The leapfrog principle still remains a reliable scheme for producing boron cages with larger HOMO–LUMO gaps, whereas the thermodynamically most stable B80 cages are formed when all pentagonal faces are capped. We show that large hollow cages of boron retain a preference for fullerene frames. The additional capping is in accordance with the following rules: preference for capping of pentagonal faces, formation of B10 and/or B16 units, homogeneous distribution of the hexagonal caps, and hole density approaching 1/9. Although our most stable B80 isomer still remains higher in energy than the B80 core–shell structure, we show that by applying the bonding principles to larger structures it is possible to construct boron cages with higher stabilisation energy per boron atom than the core–shell structure; a prototypical example is B160. This clearly shows the continuous competition between the two suggested construction schemes, namely, the formation of multiple‐shell structures and hollow cages. 相似文献
88.
Hong Tho Le Chen‐Gang Wang Atsushi Goto 《Angewandte Chemie (International ed. in English)》2020,59(24):9360-9364
Liquid vinyl monomers were converted into solid crystals via halogen bonding. They underwent solid‐phase radical polymerizations through heating at 40 °C or ultraviolet photo‐irradiation (365 nm). The X‐ray crystallography analysis showed the high degree of monomer alignment in the crystals. The polymerizations of the solid monomer crystals yielded polymers with high molecular weights and relatively low dispersities because of the high degree of the monomer alignment in the crystal. As a unique application of this system, the crystalized monomers were assembled to pre‐determined structures, followed by solid‐phase polymerization, to obtain a two‐layer polymer sheet and a three‐dimensional house‐shaped polymer material. The two‐layer sheet contained a unique asymmetric pore structure and exhibited a solvent‐responsive shape memory property and may find applications to asymmetric membranes and polymer actuators. 相似文献
89.
A density functional theory study of small base molecules and tetrahedral and cubane-like group V clusters encapsulated in B(80) shows that the boron buckyball is a hard acid and prefers hard bases like NH(3) or N(2)H(4) to form stable off-centered complexes. In contrast, tetrahedral and cubane-like clusters of this family are metastable in the cage. The most favorable clusters are the mixed tetrahedral and cubane clusters formed by nitrogen and phosphorus atoms such as P(2)N(2)@B(80), P(3)N@B(80), and P(4)N(4)@B(80). The boron cap atoms are electrophilic centers, and prefer mainly to react with electron rich nucleophilic sites. The stability of the complexes will be governed by the size and electron donating character of the encapsulated clusters. B(80) forms stable complexes with hard materials where a bidentate interaction of the encapsulated molecule with two boron cap atoms is preferred over a single direct complex toward a single endohedral boron. 相似文献
90.