Materials Literature
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Dendrimers are well-defined, highly branched macromolecules that emanate from a central core and are synthesized through a stepwise, repetitive reaction sequence. The synthesis and characterization of dendritic boxes, based on the construction of a chiral shell of protected amino acids onto poly(propyleneimine) dendri…
An absolute pKa value of about 36 in acetonitrile is obtained for porphyrin from its reaction with phosphazene bases. The monoanion 1 is stable in aprotic solvents and was characterized by NMR and UV/ Vis spectroscopy. The remaining central proton in the monoanion migrates between the four nitrogen atoms much faster t…
Isolated fibers the thickness of a molecule but more than 104 molecules long are present in the gel formed from a solution of 1 in chloroform. This molecular stack may be seen as a molecular cable containing many wires and constructed from a stack of phthalocyanine units, four stacks of crown ether units, and a surrou…
We study the antiferrodistortive instability and its interaction with ferroelectricity in cubic perovskite compounds. Our first-principles calculations show that coexistence of both instabilities is very common. We develop a first-principles scheme to study the thermodynamics of these compounds when both instabilities…
The threshold energy surface for permanent atom displacements in copper at 550 K is determined by observing the growth of interstitial-type dislocation loops during electron irradiation in a high-voltage electron microscope. Comparison with the results of King et al. and Baily et al., obtained by measurements of the r…
In situ measurements of the dislocation mobility in polycrystalline silicon are carried out in a 1000 kV high voltage electron microscope (HVEM) using a heating-straining stage at temperatures between 530 and 780 °C. Most of the dislocations are found to move in the (111) [101] glide system. The effective shear stress…
The low-temperature structure of A1C60 (A=K, Rb) is an ordered array of polymerized C60 chains, with magnetic properties that suggest a non-metallic ground state. We study the paramagnetic state of this phase using first-principles electronic-structure methods, and examine the magnetic fluctuations around this state u…
The effect of carbon diffusion from CH4 gas into coarse Sm2Fe17 powder on the magnetic domain structure (MDS) was studied at room temperature by means of the magneto-optical polar Kerr effect. The diffusion occurs initially along preferential paths and then through the bulk. A gradual variation in the MDS through inco…
The reactions with hydrogen of the C15-type Laves phase Tb0.27Dy0.73Fe2 have been studied by differential thermal analysis and the influence of this hydrogenation upon the magnetic properties was observed with a Curie–Faraday balance and a vibrating sample magnetometer. It has been found that a slightly rare earth ric…
An atomic diffusion mechanism (voidal diffusion) is proposed where nitrogen atoms migrate inside the Sm2Fe17 lattice by jumping from a 9(e) site into a thermodynamically unstable tetrahedral 18(g) site and subsequently into a new 9(e) site. For the first time, the anisotropic nature of diffusion and growth kinetics to…
The kinetics of solid-HDDR (hydrogenation, disproportionation, desorption, recombination) processing of Nd-Fe-B-type alloys have been characterized by means of in situ electrical resistivity measurements and hydrogen absorption and desorption studies on nondecrepitated samples. The fundamental differences in reaction…
Abstract An ESR method was used to study the structure of the macroradical of the propagating chain R p in the low‐temperature, solid‐phase polymerization of p ‐diethynylbenzene (DEB). The ESR spectra for γ‐irradiated DEB samples and those of DEB deuterated in the ethynyl group showed that in the range 77–230 K, the u…
Addition of tungsten (1–2 at. %) is very effective in improving coercivity of (Nd,Dy)-(Fe,Co)-B sintered magnets both at room temperature and elevated temperatures in addition to improving thermal stability. Transmission electron microscopy shows that there exists a WFeB precipitate phase inside the Nd2Fe14B (2-14-1)…
The Fe57 Mössbauer spectra of Sm2Fe17−xAlx, where x=0, 1.0, 2.0, 3.0, and 4.0, have been measured at room temperature and analyzed. The ternary compounds Sm2Fe17−xAlx have the rhombohedral Th2Zn17 structure. Mössbauer measurements showed that all the compounds studied were ferromagnetic. The average hyperfine field wa…
Raman scattering spectra of PbTe films, grown by laser-assisted deposition on a KCl substrate, containing the metastable GeS-type phase of PbTe, are investigated at different temperatures in the range 64--300 K. The Raman-active modes of the orthorhombic GeS-type phase of PbTe are detected in the low-temperature spect…
In previous work it was discovered that the 2:17-type rare-earth–iron compounds with high carbon concentration could be formed by the substitution of Ga, Si, or Al, etc., for Fe in R2Fe17Cx. The effect of Al substitution for Fe on the structure and magnetic anisotropy of Sm2Fe17C has been investigated. Alloys with the…
The structure of the fully protonated hexamolybdoplatinate polyanion salt K 2 [H 6 α-PtMo 6 O 24 ] . 5H 2 O has been determined from X-ray diffraction data. This polyanion has a center of symmetry and protonation of the O atoms is different from that of heteropolyanions having the socalled Anderson structure, [X n+ (O…
The absorption of hydrogen by NdFeB alloys in aqueous solution has been investigated using dc electrochemical methods and x-ray diffraction. Immersion of the NdFeB alloy in 0.1 M H2SO4 results in the formation of the Nd2Fe14BH2.7 hydride phase as indicated by x-ray diffraction analysis. The hydrogen entering the NdFeB…
Highly anisotropic SmCo based films with the TbCu7-type structure have been sputter deposited directly onto YIG substrates. The SmCo crystallites have the c axes approximately randomly splayed about the substrate plane such that the easy direction of magnetization of the SmCo film is in the film plane. The in-plane st…
The compound SmCo4B is a hard magnetic material; however, the saturation moment and the Curie temperature need to be increased for the compound to be a candidate for a permanent magnetic material. For this purpose, Fe substitution for the Co and Pr substitution for the Sm of SmCo4B have been attempted. In addition, th…