Fee phase

The C-C linkage in tire polymeric [60]fullerene composite is highly unstable and, in turn, tire reversible [2+2] phototransfonnation leads to an almost quantitative recovery of tire crystalline fullerene. In contrast tire similarly conducted illumination of [70]fullerene films results in an irreversible and randomly occurring photodimerization. The important aspect which underlines tire markedly different reactivity of tire [60]fullerene polymer material relative to, for example, tire analogous [36]fullerene composites, is tire reversible transfomration of tire fomrer back to the initial fee 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. 

Bamboo-shaped tubes. A carbon tube with a peculiar shape looking like bamboo, produced by the arc evaporation of nickel-loaded graphite, is shown in Fig. 8. The tube consists of a linear chain of hollow compartments that are spaced at nearly equal separation from 50 to 100 nm. The outer diameter of the bamboo tubes is about 40 nm, and the length typically several /im. One end of the tube is capped with a needle-shaped nickel particle which is in the normal fee phase, and the other end is empty. Walls of each compartment are made up by about 20 graphitic layers[34]. The shape of each compartment is quite similar to the needle-shape of the Ni particle at the tip, suggesting that the Ni particle was once at the cavities. 

For alloys containing up to about 27% Ni in Fe, the equilibrium phase at room temperature is bee. However, in the neighborhood of 30% Ni either the fee or bee phases can be obtained at room temperature as the result of various heat treatments. For nickel concentrations greater than 30%, the structure is fee. Hence, the unusually large volumetric phenomena are characteristic of the fee phase. 

The pressure sensitivity of the magnetic properties of the Invar alloys is indicated by extensive measurements of the coefficient of saturation magnetization change with pressure M dMJdP for various compositions as shown in Fig. 5.10. The exceedingly large values in the 30%-40% Ni range are evident and much in excess of the values for iron and nickel. The 30-wt% Ni composition in the fee phase is the most sensitive to pressure, whereas this... 

Fig. 5.10. The pressure dependence of saturation magnetization for iron-nickel alloys shows a strong pressure dependence in the neighborhood of the Invar alloys (28.5 to 40-at. % nickel in the fee phase). The shock data shown are in excellent agreement with the static high pressure data (after Wayne [69W01]).

Fig. 5.13. The stress-volume relations of fee and bee alloys show the strong compressibility anomaly in the fee phase below 25 kbar (2.5 GPa) associated with the magnetic interactions. Above 25 kbar, the fee alloy has a normal value for compressibility (after Graham et al. [67G01]).

With increasing values of P the molar volume is in progressively better agreement with the experimental values. Upon heating a phase transition takes place from the a phase to an orientationally disordered fee phase at the transition temperature where we find a jump in the molar volume (Fig. 6), the molecular energy, and in the order parameter. The transition temperature of our previous classical Monte Carlo study [290,291] is T = 42.5( 0.3) K, with increasing P, T is shifted to smaller values, and in the quantum limit we obtain = 38( 0.5) K, which represents a reduction of about 11% with respect to the classical value. 

Figure 1. The energy of bcc and hep randoiri alloys and the ])ai tially ordered a phase relative to the energy of the fee phase (a), of the Fe-Co alloy as a function of Co concentration. The corresponding mean magnetic moments are shown in (h). The ASA-LSDA-CPA results are shown as a dashed line for the o ])hase, as a full line for the her ]>hase, as a dot-dashed line for the hep phase, and as a dotted line for the fee phase. The FP-GGA results for pure Fe and Co are shown in (a) by the filled circles (bcc-fcc) and triangles (hep-fee). In (b) experimental mean magnetic moments are shown as open circles (bcc), open scpiares (fee) and open triangles (hep).

We found that without any exception in all of our simulations Bain s lattice correspondence actually applies, i.e. one set of (110) planes of the bcc structure corresponds to a set of fee (111) planes, while the bcc [001] direction lying in these planes is transformed into the [110] direction of the fee phase. Moreover, these directions are exactly parallel to each other. This would correspond to a Nishiyama-Wassermann orientational relationship if the (110) and (111) planes would also be parallel to each other. But this is not the case. These planes are rotated around [001] by an angle between 0 and 9 during the transformation. This angle differs between the simulations in a non-systematic way. 

The study of ultra-thin Fe thin films on Cu(OOl) substrate has attracted a lot of interest in the past. This is due to the abundance of interesting phenomena associated with this system. Due to the small epitaxial misfit a good layer by layer growth is expected stabilizing the film in a structure related to the fee phase of bulk Fe which is otherwise unstable at low temperatures It also become a test system for magnetic measurements. 

Figure 2. Total energy for FeaNi along the Bain path with V = const (a). Binding energy versus volume of the unit cell for the ferromagnetic (FM) bet (circle) and fee (square) states. Diamonds results for the nonmagnetic (NM) fee phase.

The mean-field phase diagram in the WSL calculated by Matsen et al. [138] predicts a transition from C to the disordered state via the bcc and the fee array with decreasing /N. This was not followed here. Transitions from the C to S (at 115.7 °C), to the lattice-disordered sphere - where the bcc lattice was distorted by thermal fluctuations - and finally to the disordered state (estimation > 180 °C but not attained in the study) were observed. It was reasoned to consider the lattice-disordered spheres as a fluctuation-induced lattice disordered phase. This enlarges the window for the disordered one and causes the fee phase to disappear. Even if the latter should exist, its observation will be aggravated by its narrow temperature width of about 8 K and its slow formation due to the symmetry changes between fee and bcc spheres. 

Bulk Ag-Al alloys, containing up to 12 a/o Al, were electrodeposited from melt containing benzene as a co-solvent. Examination by x-ray diffraction (XRD) indicated that the low-Al deposits were single-phase fee Ag solid solutions whereas those approaching 12 a/o were two-phase, fee Ag and hep i>-Ag2Al. The composition at which ti-Ag2Al first nucleates was not determined. The maximum solubility of aluminum in fee silver is about 20.4 a/o at 450 °C [20] and is reduced to about 7 a/o at room temperature. One would expect the lattice parameter of the fee phase to decrease only slightly when aluminum alloys substitutionally with silver because the... 

These non-existent allotropes, which are impurity-stabilized phases, are fee Sc, fee Y-Ce, the bcc Ho, Er, Tm and Lu and fee phases of Nd, Sm, Gd and Dy, some of which have been described as formed at room temperature during mechanical milling. A number of fee high-pressure polymorphs, for instance, are actually compounds, with a structure related to the NaCl-type, formed by reaction with O, N and/or H during mechanical milling (see also Alonso et al. 1992). 

In 2008, the A15 or body-centered cubic (bcc) CssCgo phase, which shows bulk superconductivity under applied hydrostatic pressure, was obtained, together with a small amount of by-products of body-centered orthorhombic (bco) and fee phases, by a solution process in liquid methylamine (Prassides, Rosseinsky, et al.) [312]. Interestingly, the lattice contraction with respect to pressure results in an increase in Tc up to around 0.8 GPa, above which Tc gradually decreases. The highest Tc is... 

---