Polycrystalline samples

The process of sintering by vapour phase transport is probably important to the growth of single crystals of solids from polycrystalline samples in a closed system, where the vapour species are the transporting gas, which may have the same or different chemical composition from die solid. An example where... 

Surface-sensitive diffraction is, for the most part, restricted to analysis of surfaces of single crystals and overlayers and films on such surfaces. If a polycrystalline sample is illuminated using a beam of low-energy electrons, each crystallite surfiice exposed will create its own diffraction pattern, all of which will be superimposed on the fluorescent screen detector. If more than a few orientations are illuminated by the beam, the pattern becomes too complicated to analyze. Flowever, if the size of the... 

Crater Bottom Roughening. Depth resolution is also limited by roughening of the crater bottom under the action of ion bombardment. On polycrystalline samples this can be because of different sputter yields of different crystal orientations, because the sputter yields of single crystals can vary by a factor of two depending on their orientation. Because of this type of roughening, depth resolution deteriorates with increasing sputter depth. 

A single triplet has three resonant fields, two due to Amv= l transitions and one due to Ams 2 transitions. For amorphous or polycrystalline samples, two triplet powder patterns are formed due to contributions from all possible orientations of triplets with respect to the applied field. The full-field triplet powder pattern due to Ahia-= 1 transitions is centered about If and has the following critical points ... 

Indirect methods used can profit by the thermodynamic data of a particular metal-hydrogen system. The determination of the H/Me ratio after complete desorption of hydrogen from a sample, despite an apparent simplicity of the method, gives adequate results only when the bulk metal sample was entirely saturated with hydrogen, and that is a very rare case. The metal catalyst crystallites can be saturated in a nonuniform way, not through their whole thickness. The surface of this polycrystalline sample varies to such extent in its behavior toward interaction with hydrogen that hydride forms only in patches on its surface. A sample surface becomes a mosaique of /3-hydride and a-phase areas (85). 

The infrared spectra have been reported for polycrystalline samples of [NilSaCPh) ] and [Zn(S3CPh)2]. The nickel compound has two molecules per unit cell on sites of Cj symmetry, and assignment of a weak absorption at 655 cm to pIS-S) has been made (369). 

The four tellurium compounds are obtained as polycrystalline samples by annealing stoichiometric amounts of the elements in sealed silica or Pyrex tubes at temperatures between 280 (AuTel) and 350°C... 

Benzene, benzene-t/i, CFCI3 and CF3CCI3 were obtained commercially and were not further purified. Solutions of c a 0.3 - 1 volume % of benzene in CFCI3 were prepared in suprasil quartz tubes of 4 mm outer diameter on a vacuum line. The samples were degassed and sealed under vacuum (< 10-4 -porr). Polycrystalline samples were prepared by rapid freezing in liquid nitrogen. The samples were irradiated at 77 K for 5 minutes at an approximate dose rate of 250 G/min. using the radiation from an X-ray tube with a W anode operated at 70 kV and 20 mA. 

We note, however, that there have been instances of mistaking polycrystalline samples for truly amorphous ones. 

The Incident Ion beam Intensity can be measured, and there are several tabulations of cross-section calculations. ( ) Also, the analyzer parameters, T, D, and d6 can be determined. The three aspects of this equation, which are not well understood nor easily determined. Include the number of atoms of a particular kind, the Ion survival probability, and the shadowing or geometric term. The first quantity Is quite often that which you would like to determine. The second two are often difficult to separate. Shadowing can be particularly Important when trying to observe second layer effect or when trying to determine the location of adsorbates.( ) However, shadowing for polycrystalline samples, though Important, Is very difficult to deal with quantitatively. 

Polycrystalline samples of these materials have a room-temperature conductivity of about 0.5 S/m, but at 300°C the conductivity is about 10 S/m. 

In the case of resonance absorption of synchrotron radiation by an Fe nucleus in a polycrystalline sample, the frequency dependence of the electric field of the forward scattered radiation, R(oj), takes a Lorentzian lineshape. In order to gain information about the time dependence of the transmitted radiation, the expression for R(oj) has to be Fourier-transformed into R(t) [6]. 

Semiconductor films of ZnO used as operational elements are obtained by oxidation at - 500 - 600°C in the jet of purified oxygen of zinc film deposited at vacuum iP 10 Torr) on substrates made of fused quartz with subsequent sintering at - 350°C at high vacuum conditions [34]. As it was concluded in paper [17] the sintered polycrystalline sample obtained in such a manner should not be considered as a set of various separate crystallites touching each other but rather as a monolithic pattern in which microcrystals with diameter of 1-10 pm are linked with each other by bridges with length and thickness of the order of 0,1 pm (see Fig. 2.4). 

Disregarding the crystal size distribution in a polycrystalline sample, the observed profile of any peak... 

Polydispersity Different Crystal Size Averages. The crystal sizes in the polycrystalline samples are not identical. So it is important to know, what kind of average (cf. Sect. 1.2) is returned by the method. 

For the hydrogen atom, two such resonance conditions occur, giving rise to two lines separated by 506 G, which is just the value of a for the hydrogen atom [Eq. (ID)]. The spectrum would look the same for a single crystal or for a polycrystalline sample because the g factor and the hyperfine constant are isotropic. 

One should realize, however, that for polycrystalline samples it is not possible to assign one of the principal g values to a particular molecular axis on the basis of experimental data alone. Such assignments usually are rationalized from theoretical considerations. 

In addition, Janczak [26] studied the conductivity property of complex 3 with a polycrystalline sample, and the results show that the conductivity is in the range 2.7 -2.8 x 10-2Q-1cm-1 at room temperature. Very weak temperature dependence of the conductivity and a metallic-like dependence in conductivity are observed in the range 300-15 K. Ibers and co-workers [70] investigated the electrical conductivity of partially oxidized complex 82 with a suitable single crystal and the results indicate its semiconductor nature (Ea = 0.22eV). 

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