Tungsten diffraction pattern

Fig. 8 Part of the 2D diffraction pattern obtained from a twinned single-crystal of Te-III at 7.4 GPa. The main body-centred monoclinic reflections from the two twin components are shown, indexed hk[) and (hkl)2- The satellite reflections are marked with asterisks, and a powder line from the tungsten gasket is marked G . D marks a reflection from one of the diamond anvils...

EXAMPLE 9.7 Comparison Between Bulk and Surface Structures Using Low-Energy Electron Diffraction Patterns. If we accept that an LEED pattern has the same symmetry as the net of surface atoms responsible for its formation, what additional information is needed to complete the comparison between bulk and surface structures for the tungsten surface shown in Figure 9.16a ... 

Figure 2. The X-ray diffraction patterns from the deposited films prepared by pulsed laser deposition using tungsten oxide (WO3) target with different partial pressure of oxygen.

Complete the solution of the crystal structure and perform Rietveld refinement of the model of tungsten oxide peroxide hydrate, W02(02)(H20), which crystallizes in the space group symmetry P2]/n with a = 12.07, b = 3.865, c = 7.36 A, p = 102.9". The location of W has been found from a Patterson map and it has the coordinates x = 0.680, y = 0.066, z = 0.364. Note that W usually exhibits octahedral or square-pyramidal coordination (with the peroxide group, 0-0, counted as one ligand). The experimental powder diffraction pattern is found on the CD in the file Ch7Pr08 CuKa.raw. 

OL-Tungsten is the only stable modification. It has a body-centered cubic lattice of space group - Im3m (No. 229). A diffraction pattern is shown in Fig. 1.7, together with a crystal structure model. 

We cut an AIN/W FGM sample (W content from 0 wt% to 30wt%) and performed X-ray diffraction on the cut surface using the Ka waves of Cu at 1 mm intervals. The results are shown in Fig. 3. As a result of identifying the compound phases formed in the AIN/W FGM sintered body from the positions of the peaks shown in the X-ray diffraction patterns, we confirmed the existence of aluminum nitride and metallic tungsten. Fig. 3 shows the results of X-ray diffraction at all measurement points. The measurement points indicate the presence of... 

Fig. 6. Low energy electron diffraction patterns at normal incidence from clean tungsten surfaces, (a) Ball model of W(llO) face. Some of the net lines (hk) are indexed in terms of a centered rectangular unit mesh (outlined), (b) Clean W(llO), 75 V. Diffuse brightness and central bright spot are caused by light from electron gun filament, (c) Clean W(llO), 300 V. (d) Ball model of (112) surface, the third densest of the boo lattice, (e) Clean W(112) at 90 V. Note the asymmetric intensities of the A/c and hA beams. The unit mesh contains only a single mirror plane perpendicular to surface. There is a strong scattering contribution from the exposed second layer which is asymmetrically positioned.

These first LEED experiments have not yet led to understanding of NHg decomposition or synthesis on W. Effects of H2 or Ng coadsorbing with NHg or NHj still remain to be investigated and one can anticipate many more interesting experiments before the work is completed. It is appropriate to mention briefly that LEED study of NHg decomposition on a Si(lll) surface (293) reveals some similarities to the tungsten experiments. Low energy electron diffraction patterns attributed to N atoms on the surface are developed by heating a room temperature deposit above 700°C. These patterns could not be interpreted in terms of thin layers of silicon nitride. 

Figure 27.29 shows a powder diffraction pattern obtained by mounting a capillary tube filled with fine tungsten powder in the center of the diffractometer illustrated in Fig. 27.28. The numbers on the peaks are the indices of the planes which produce that peak. By measuring the values of 9, the interplanar spacing can be calculated from the Bragg equation.

Use a tungsten or copper X-ray source and a powder diffractometer. Load cmshed NaCl powder into the sample holder. Measure the diffraction pattern of the NaCl. Repeat with powdered KCl. Note the difference in spectra. Make mixtures by varying the amounts of NaCl and KCl. Can you distinguish the mixtures and the relative amounts of each component from the powder patterns ... 

Figure 1. X-ray powder diffraction pattern of tungsten oxide surfactant indexed on a hexagonal unit cell with a=b=4.5 nm.

Diffraction patterns can be obtained from random sources, such as tungsten filaments, provided that an arrangement similar to that shown in Figure 6-8a is employed. Here, the very narrow slit A assures that the radiation reaching H and C emanates from the same small region of the source. Under this circumstance, the various wave trains that exit from slits 8 and C have a constant set of frequencies and phase relationships to one another and are thus coherent. If the slit... 

Figme 3.26 shows the first five peaks of the x-ray O diffraction pattern for tungsten (W), which has a... 

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