Poly crystalline sample

A typical dc susceptibility-versus-temperature transition curve for polycrystalline LuNi2E>2C and YNi2E>2C with Tc 16.5 K and 15 K, respectively, is shown in Figure 1. The growth of very high-quality single crystals of nickel borocarbide superconductors (see, e.g., Xu et al., 1994) almost immediately after their discovery has had a profound impact on the quality of the work performed. Thus many of the pitfalls of the early research on other complex materials, such as high-Tc superconductors, carried out on poly crystalline samples of variable quality, have essentially been avoided (Cava, 2001). 

Fig. 14 A The emission spectrum from a chloroform solution of Au fMeN = COMe)3. B The emission spectrum from a polycrystalline sample of Au fMeN = COMe)3. C The spectrum of the light emitted from a poly-crystalline sample of AuVMeN = COMe)3 after UV irradiation and contact with a drop of chloroform. From [43]...

The (1120) faces, dominant on poly crystalline samples, are characterized by highly shielded fivefold Fe3+ ions (5.43 A apart) and partial homopolar character. The situation is similar to that encountered on prismatic (1120) faces of (y-Cr20, after sintering under severe conditions. When probed with CO, Fe3+ ions exposed on the (1100) surfaces form weak Fe3+ CO adducts, characterized by a very modest shift of the C-0 stretching mode relative to the gas phase value (v = 2164-2165.5 cm A v = 20-22 cm-1). It is thus concluded that the local electric fields associated with Fe3+ ions at the surface of (1100) faces are very weak and similar to those reported for Mg2+ on MgO (001) and Cr3+ on (y-( r202 (1120) surfaces. 

Often, it is not possible to obtain single crystals that are large enough to be worked with in a convenient manner. In those cases, physical properties must be measured on poly crystalline samples. There is always discrepancy, or disagreement, between measured physical properties of single crystals and polycrystals due to microstructural effects. Hence, physical properties measured from polycrystalline samples are sometimes considered less reliable from a reproducibility standpoint. 

Fig. 91 Cyclic voltammetry on Ft in 0.5 M (a) poly crystalline sample, 15 mVIs (b) spherical singlecrystal Pt electrode, 50 mVIsec. Reprinted with permission from Clavilier and Armand, J. Electroanal. Chem. 199 187. Copyright 1986 Elsevier Sequoia.

Figure 2.16. Left oxygen diffusion data of various ceria-coniaining materials 1 CeOj. single crystal 2 CeOj poly crystalline sample 3 CeogYojOiv 4 CCo Yo Oig 5 CeO,g 6 Ceo9Cao,0,/ 7 (0.3%)Od doped CcOj 8 Ce02. shaded area corresponds to oxygen diffusion values calculated from ionic conductivity of rare-earth doped ceria CC. M 02.o,. with x 0.2 and 0.3 using Eq. 2.29. Right details of oxygen diffusion coefficients of rare-earth doped ceria with x=0,3 from top to the bottom (M=Eu,Nd.Ho,Gd.Er.Sm,Y.La.Yb,Dy).

Ultrasonic interferometry, in which the travel time of high-frequency elastic waves through a sample is measured, also yields elastic moduli. Because it is a physical property measurement, rather than an optical spectroscopy, it can be used equally well on poly-crystalline samples as single-crystals, although polycrystalline measurements only yield the bulk elastic properties, bulk modulus and shear modulus, G. High-pressure ultrasonic interferometry techniques were initially developed in the piston cylinder... 

All of the fore-going techniques to measure the elasticity of materials actually determine the elastic or phonon wave velocities, both of compressional (Vp for /7-waves) and transverse waves (Vs for 5-waves) in the sample. The bulk and shear moduli of a poly crystalline sample are given by ... 

A single triplet has three resonant fields, two due to Ah7s = 1 transitions and one due to Am.s= 2 transitions. For amorphous or poly crystalline 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 Ams= l transitions is centered about Hq and has the following critical points ... 

The normals to each family of planes for each of the crystals in the sample are defined by the vector of the reciprocal lattice. In the case of a poly crystalline sample, the total number of these vectors is The tips of these vectors form... 

Microstructural Study of Randomly Oriented Poly crystalline Samples 245... 

For poly crystalline samples, the parentheses in Eq. (11) are replaced by a distribution function. The line shape of the powder spectrum has been discussed for spin / = 3/217 and / = 114 nuclei with various values of rj. In general, for / = 1 it shows singularities at (yH0(2ir) 3e2qQ( — q)fSh, shoulders or distribution edges at (yH0/2v) ... 

Figure 12. Infrared spectra of KN3 transmission of poly crystalline sample (upper) reflection from single-crystal samples (lower).

Lastly, in the following discussion the term structure connotes molecular structure at the subcrystal level and includes both electronic bonding, as discussed in Chapter 5, and the spatial, dynamic, and energetic aspects of atomic configuration, as discussed in Chapters 3 and 4. Macrostructure is used to describe the nature of poly crystalline samples down to the level of individual crystals and their internal and external surfaces. 

Fig. 6.1. The thermal expansion coefficient a of ice as determined for poly-crystalline samples by Jakob Erk (1928), — for single crystals by Hamblin...

In a powdered or poly crystalline sample each unique set of diffracting planes hkl will produce a cone of diffracted rays that will be centered around the undiffracted X-ray beam with a radius of (Fig. 5) (Flemming 2007). 

An analysis of Eqs. (18) and (19) and of the formulas in Table 4 shows that AEgy — 0 for the p states. This means that there is no anisotropy in the scattering of x rays or electrons by a poly crystalline sample. 

A more recent study employed both direct and indirect covariance on C, N-labelled histidine in a poly crystalline sample [34]. The investigators constructed C—C and N—N correlation maps from a H—H dipolar mediated shift correlation experiment where the and FIDs were simultaneously acquired with multiple receivers. The correlation plots obtained were equivalent to CHHC, NHHN and NHHC spectra. Significant... 

E ig. 51. Temperature dependence of the line widths for the quasi-elastic single-site contributions (open squares, and for the inelastic inter-site contributions (open circles, obtained on a CeCug single crystal (Rossat-Mignod et al. 1988). Also shown are the quasi-elastic line widths measured on a poly-crystalline sample by a time-of-flight (TOF) technique (IN6, solid circles) (Walter et al. 1986). 

The tracer diffusivity of H Ag in dense poly crystalline samples was measured at temperatures ranging from 600 to 800C, under an O partial pressure of O.lMPa, and at 700C, under O partial pressures of between IkPa and O.lMPa. Standard sectioning and counting methods were used. It was found that the results could be described by ... 

The tracer diffusion of Fe in poly crystalline samples of the a-phase was studied by using the radioactive isotope, 59Fe. The dependence of the diffusion coefficient upon the S activity and temperature was investigated. It was found that the predominant transport mechanism was volume diffusion which proceeded via point defects, and that the Fe-diffusion rate was higher than the self-diffusion of Mn in manganous sulfide. Overall, the results could be described by ... 

Finally, some special features may be found in the same column. These include references to a change of spectrum with temperature, to antiferromagnetic behaviour if it has been substantiated by EPR measurements, to the ratio of HFS splitting constants for two isotopes, to nuclear quadrupole moments determined from EPR results and other similar information. For some poly crystalline samples, the half width AHm of the line has also been included. 

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