Composition and crystal structure parameters of single crystals (Bi, Pb)2Sr2(Ca1−xRx)Cu2O8+δ (R = Y, Er, Ho, Tm, and Yb)Journal of Materials Research - Tập 8 - Trang 1791-1797 - 1993
A. S. Ilyushin, L. Shi, L. I. Leonyuk, B. M. Mustafa, I. A. Nikanorova, S. V. Red’ko, Y. Jia, A. G. Vetkin, G. Zhou, I. V. Zubov
To correlate structural and compositional parameters in the bismuth 2212 system, single crystals with the composition (Bi1−yPby)2Sr2(Ca1−xRx)Cu2O8+δ (R = Y, Er, Ho, Tm, and Yb; y = 0, 0.1; 0 ≤ x ≤ 0.5) have been studied at room temperature by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The main results are as follows: (i) The actual content, x, of R (R = Y, Er) in samples is in significant excess over its content x′ in the melt for x′ < 0.5. The opposite effect (but several times smaller) takes place for Ca. At x′ = 0.5, the x value practically coincides with x′. (ii) For all R under examination and x′ = 0.1, the value of x is within the limits of 0.43 ≤ x ≤ 0.51; i.e., x exceeds x′ several times. (iii) The total content of Ca, R (R = Y, Er), and Sr is close to 3 through the whole range 0 ≤ x′ ≤ 0.5. At x′ < 0.5 Ca is partly substituted for Sr, while R occupies only Ca crystallographic positions. Thus the actual formula of the samples is (Bi1-yPby)2+∊Sr2-z(Ca1+z-xRx)Cu2O8+δ. (iv) The evidence was received that the nonlinear dependence c(x) at x < 0.5 is connected with the partial substitution of Sr with Ca. The dependence of c, namely on the R = Y content in the denoted range of x, is close to linear with the slope ∂c/∂x = −0.67(2) Å/at.
New nonhydrolytic route to synthesize crystalline BaTiO3 nanocrystals with surface capping ligandsJournal of Materials Research - Tập 21 Số 12 - Trang 3187-3195 - 2006
Zhuoying Chen, Limin Huang, Jiaqing He, Yimei Zhu, Stephen O’Brien
A new nonhydrolytic route for the preparation of well-crystallized size-tunable barium titanate (BaTiO3) nanocrystals capped with surface ligands is reported. Our approach involves: (i) synthesizing a “pseudo” bimetallic precursor, and (ii) combining the as-synthesized bimetallic precursor with a mixture of oleylamine with different surface coordinating ligands at 320 °C for crystallization and crystal growth. Different alcohols in the precursor synthesis and different carboxylic acids were used to study the effect of size and morphological control over the nanocrystals. Nanocrystals of barium titanate with diameters of 6–10 nm (capped with decanoic acid), 3–5 nm (capped with oleic acid), 10–20 nm (a nanoparticle and nanorod mixture capped with oleyl alcohol), and 2–3 nm (capped with oleyl alcohol) were synthesized, and can be easily dispersed into nonpolar solvents such as hexane or toluene. Techniques including x-ray diffraction, transmission electron microscopy, selected area electron diffraction, and high-resolution electron microscopy confirm the crystallinity and morphology of these as-synthesized nanocrystals.
Effect of surface conditions and strain hardening on the passivity breakdown of 304 stainless steelJournal of Materials Research - Tập 27 - Trang 1580-1588 - 2012
Tewfik Souier, Matteo Chiesa
Electrical and electrochemical properties of the passive layer formed on 304L austenitic stainless steel are investigated by means of both conductive atomic force microscopy in air and electrochemical atomic force microscopy in chloride-containing media. The maps of local electrical conductivity of the oxide overlayer exhibit different patterns depending on the surface conditions after mechanical or electrochemical polishing. In particular, the passive film covering strain-hardened regions reveals a higher electrical conductivity. The local enhancement of the electrical conduction is explained by local changes of the stoichiometry of the passive film. Moreover, the highly conductive regions lead to a local breakdown of the native oxide in chloride-containing media and favor the initiation of localized pits.
Atomic structures of nonequilibrium alloys in an immiscible Co–Ag systemJournal of Materials Research - Tập 19 - Trang 1364-1368 - 2004
H. B. Guo, B. X. Liu
A Co–Ag potential in the form of TB-SMA (the second moment approximation of the tight-binding scheme) is derived based on some ab initio calculated physical properties. Applying the derived potential, molecular dynamics simulations reveal that a Co-/Ag-based solid solution retains its atomic homogeneity up to a critical ratio of9 Ag/12 Co at.%, over which the Ag/Co solute atoms begin to segregate. Correspondingly, a cage-like configuration is proposed to have 1 Ag/Co atom isotropically surrounded by 9 Co/7 Ag atoms for the homogeneous solid solution. Moreover, when the solute atoms exceed 12 Ag/18 Co at.%, the solid solution turns into an amorphous phase with inhomogeneous atomic structure.
Transformation of Al–Ni–(Si) decagonal quasicrystals to 1–D quasicrystal and crystalline approximantsJournal of Materials Research - Tập 8 Số 10 - Trang 2499-2503 - 1993
X.Z. Li, K. H. Kuo
Rapidly quenched Al86-xNi14Six (x = 0, 2, 6, and 10) alloys have been studied by means of transmission electron microscopy. Two-dimensional (2-D) decagonal quasicrystal with a periodicity of 1.6 nm along its tenfold axis was found in the rapidly quenched Al86Ni14 binary alloy. With the addition of some silicon, such as AlgoNi14Si6, the 2-D decagonal quasicrystal first transforms to a one-dimensional (1-D) quasicrystal that inherits the periodicity along the tenfold axis and has, in addition, translation periodicity in one of the twofold axes of the decagonal phase, and finally transforms to a new orthorhombic crystalline phase (a = 0.78, b = 1.62, and c = 1.48 nm). In the Al76Ni14Si10 ternary alloy, a 2-D decagonal quasicrystal with a periodicity of 0.4 nm and a coexisting crystalline phase with the “Al3Ni2” structure were found, and their orientational relationship has been determined.
Distributions of kinetic pathways in strain relaxation of heteroepitaxial filmsJournal of Materials Research - Tập 32 - Trang 3977-3991 - 2017
Dustin Andersen, Robert Hull
The kinetic relaxation pathways for strained heteroepitaxial films are mapped using a process simulator that integrates experimental and model descriptions of the energetic and kinetic parameters that define the nucleation, propagation, and interaction of strain relieving dislocations. This paper focuses on GexSi1−x/Si(100), but the methodologies described should be extendible to other systems. The kinetic pathways for strain evolution are plotted for film growth as functions of the primary kinetic parameters: growth temperature, growth rate, and initial lattice mismatch, generating relaxation surfaces for parameter pairs. Sensitivity analyses are presented of how deviations from mean parameters disperse the resultant relaxation surfaces. Finally, multi-parameter “fingerprinting” of the dislocation array is shown to illustrate how fundamental kinetic mechanisms—particularly dislocation nucleation mechanisms—define the final dislocation array. The overarching goal is to establish a robust framework for predicting, interrogating, and optimizing strain relaxation pathways and underlying mechanisms, for misfit dislocations in strained heteroepitaxial films.
Polyacetylene as heterogeneous catalyst for electroless deposition of bulk amorphous metalsJournal of Materials Research - Tập 5 - Trang 1697-1702 - 2011
S. J. Kamrava, S. Söderholm
Polyacetylene shows catalytic activity in an aqueous solution for electroless deposition of amorphous alloys. The catalytic activity of polyacetylene is comparable to the activity of some highly catalytic metals, i.e., Cu, steel, and Pt. Modifications of the Shirakawa technique led to the formation of a foam-like polyacetylene, which is highly porous and has a low degree of crystallinity. This material can be used as a catalytic substrate for the preparation of amorphous metals in bulk form. The amorphous Ni–Co–B and Ni–Co–P alloys deposited on a PAc substrate were investigated by magneto-thermogravimetry and x-ray diffraction. These investigations gave a Curie temperature of about 413 K and a crystallization temperature of about 600 K for the metal-metalloid component of the system.
