FCC phase

Pure metallic cobalt has a soHd-state transition from cph (lower temperatures) to fee (higher temperatures) at approximately 417°C. However, when certain elements such as Ni, Mn, or Ti are added, the fee phase is stabilized. On the other hand, adding Cr, Mo, Si, or W stabilizes the cph phase. Upon fcc-phase stabilization, the energy of crystallographic stacking faults, ie, single-unit cph inclusions that impede mechanical sHp within the fee matrix, is high. 

To summarize we have reproduced the intricate structural properties of the Fe-Co, Fe-Ni and the Fe-Cu alloys by means of LMTO-ASA-CPA theory. We conclude that the phase diagram of especially the Fe-Ni alloys is heavily influenced by short range order effects. The general trend of a bcc-fcc phase transition at lower Fe concentrations is in accordance with simple band Ailing effects from canonical band theory. Due to this the structural stability of the Fe-Co alloys may be understood from VGA and canonical band calculations, since the common band model is appropriate below the Fermi energy for this system. However, for the Fe-Ni and the Fe-Cu system this simple picture breaks down. 

Here, we address the more general question of the relative stability of monomers, dimers and triangular trimers on the (111) surface of FCC transition metals of the same chemical species as a function of the d band filling Nd. All possible atomic configurations of the systems are considered monomers and dimers at sites N and F, triangles with A and B borders at sites N and F (Fig. 4). The d band-filling includes the range of stability of the FCC phase (Nd > 7.5e /atom). The densities of states are obtained from... 

The same alloy milled for 80 h did not absorb hydrogen. It seems that the presence of the FCC phase formed during milling somehow blocks the hydrogen intake but the exact explanation is lacking. 

Face-centred cubic (FCC) structures have also been observed in Pluronic copolymers, using SAXS (Berret et al. 1996). In an aqueous poly(oxyethylene)-poly(oxybutylene) (PEO-PBO) diblock solution, both BCC and FCC phases... 

Beta-stimulated conductivity of Cgo single crystal in an interval 230 value obtained of activation energy Efcc = 0.17 eV is close to an activation energy of photoconductivity E = 0.2 eV [3] (Fig. lc). A decrease of an activation energy to... 

FIGURE 11.13 Phase diagram plotted as particle density, >, versus salt concentralion for particle charge Z = 400 (a) particle diameter of 0.109 un, (b) particle diameter of 0.234 p.m, (c) particle diameter of 0.400 /am. The BCC—FCC phase boundaries are the same for the three cases, but the liquid-solid phases boundaries are pushed to lower densities as the particle size is increased. Taken from Shih et al. [48]. Reprinted by permission by El vier Science Publishing. 

Zhang J. and Guyot F. (1999a) Experimental study of the bcc-fcc phase transformations in the Fe-rich system Fe-Si at high pressures. Phys. Chem. Mineral. 26, 419-424. 

This should be the case for the A site and C site because they have the same energy level with respect to gravity, so RHCP would be favored in colloidal sedimentation. In order to quantitatively define the amount of the FCC phase versus the HCP phase, an overall stacking parameter, a, is used. This stacking parameter is defined such that a = 0 for the HCP, a = 1 for the FCC phase, and a RHCP structure would have an a = 0.5. This has been used to describe colloidal crystal structure and stacking fault density. ... 

FCC phase was ascertained by the emergence of a set of crystalline Bragg peaks as described previously. Experimental results for the liquid phase are shown in Fig. la, as well as the total radial distribution function for the FCC phase (calculated as G(r) = 1 + Po (2ti) FT [S(q) - 1], where FT means Fourier Transform). For a description of data treatment see in this series the paper entitled Neutron diffraction as a tool to explore the free energy landscape in orientationally disordered phases or ref. ( ). 

Figure La) Scattering function for liquid Carbon Tetrachloride together with its determination by means of molecular dynamics and Reverse Monte Carlo (RMC). With dotted lines we show the determination of the intramolecular structural parameters determined by the Bayesian method described in the text, b) Total radial distribution function for the FCC phase, together with the results of RMC.

Figure 3. Molecular Coordination Number (MCN) as a function of the distance, for the liquid phase (filled circles MD, empty circles RMC) and the FCC phase (squares). Arrows show the maxima of MCNfor the aforementioned phases, i.e., the maximum of local density.

Figure 6. (Color online) Comparison of the positional ordering obtained for the liquid phase (a,b,c) and for the FCC phase (d) by means ofMD simulation. Color scale is defined as in Fig. 5.

The interest in thin metal films on metal substrates is mainly due to the possibility of using the interaction with the substrate to stabilize and ereate ciystallographic structures of the adsoibate elements, which are inexistent or only stable under elevated tenperature or pressures in its bulk [85Pri]. The most famous exanqjle is the stabilization of fcc-Fe down to low temperature by the growth on Cu(lOO) [67Jes, 68Jes] (bulk Fe exists in the fcc-phase only from 1200 - 1650 K, otherwise it crystallizes in a bcc lattice). 

Kow] Kowalski, M., Spencer, P.J., Thermodynamic Revaluation of the Cr-O, Fe-O andNi-O Systems Remodelling the Liquid, BCC and FCC Phases , Calphad, 19(3), 229-243 (1995) (Assessment, Phase Diagram, Phase Relations, Thermodyn., Review, 47)... 

Takemura K, Kobayashi K, Arai M (1998) High-pressure bct-fcc phase transition in Ga. Phys Rev B58 2482-2486... 

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