Metals crystal phase transitions

Raman spectra were measured on fresh, chemically etched surfaces in quasi-backscattering configuration using a triple DILOR XY spectrometer, a liquid nitrogen cooled CCD detector, and a 514.5-nm Ar-ion laser. The laser beam of power level 20 mW was focused on an area of 0.1 mm2 on the mirror-like plane (it was the (ab) plane of the single crystals). The measurements were performed in a cryostat with a helium gas atmosphere in the temperature range 5-295 K below temperature of metal-insulator phase transition. 

We have studied the resistance and thermopower behavior of the p -phase [9]. From the temperature-dependent resistance curve, one can see clearly a metal-semiconductor phase transition at about 140 K (Fig. 2), whereas on the temperature-dependent thermopower curve, only a very small (but distinct) kink appears at the same temperature (Fig. 3). To interpret these seemingly conflicting phenomena, a two-energy band model was used [9]. In this model, the conductivity is due to a combination of the two bands, and the thermopower is due to a competition of the two bands. From the room-temperature X-ray diffraction, which shows the iodine atoms arranged randomly, we speculate that, at room temperature, there should be an energy gap at the Fermi surface, but that the random arrangement of iodine atoms smears the gap. Thus, the crystal stays metallic at room temperature. 

Many beam lattice images obtained at 200 kV from thin regions (5nm) in V2O3 crystals for showing the importance of the defocus value and crystal thickness to interpret the images in crystals of relatively small unit cells (two molecule rhomboedral cell with ur = 5.473nm and a = 53.79°). This crystal depicts also a metal-semiconductor phase transition at about 150 K, which can be easily observed by HREM [16]. 

Complete dispersion curves along symmetry directions in the Brillouin zone are obtained from calculated force constants. Calculations of enharmonic terms and phonon-phonon interaction matrix elements are also presented. In Sec. IIIC, results for solid-solid phase transitions are presented. The stability of group IV covalent materials under pressure is discussed. Also presented is a calculation on the temperature- and pressure-induced crystal phase transitions in Be. In Sec. IV, we discuss the application of pseudopotential calculations to surface studies. Silicon and diamond surfaces will be used as the prototypes for the covalent semiconductor and insulator cases while surfaces of niobium and palladium will serve as representatives of the transition metal cases. In Sec. V, the validity of the local density approximation is examined. The results of a nonlocal density functional calculation for Si and... 

Even though the fast scanning calorimeters were developed for metal samples, they were also successfully applied to the melting of PE single crystals, phase transitions in two-dimensional self-assembled hexadecanethiol monolayers, and the glass transition in ultrathin spin-coated polymer films. Figure 15 shows typical curves for the glass transition in nanometer-thick polymer films. From these... 

Pd(lll). However, Pd(lll) shows little or no evidence for the stoichiometric 2Bi + L + 3L process. This could be due to the presence of longer range order on the single crystal than on the Pd particles, leading to processes more akin to two dimensional phase transitions on the Pd(lll) crystal surface, rather than a more local species conversion on the small metal crystallites. 

Selection-coupled analysis/phase segregation. One strategy for simplifying the analytical challenge is to use phase segregation. Three subclasses are possible. In the first of these, a phase transition is part of the selection process. This includes not only the familiar crystallization-induced enantiomeric enrichment discussed above but also the experiments (primarily employed in experiments directed toward the production of novel materials) such as those described by Lehn and coworkers in 2005. In this study, an acylhydrazone library was created from guanosine hydrazide and a mixture of aldehydes (Fig. 1.22) in the presence of metal ions, formation of G-quartet structures led to the production of a gel. 

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