. An unknown crystal is either KCI or KBr. The d-spacing of the (220) reflection
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Question
. An unknown crystal is either KCI or KBr. The d-spacing of the (220) reflection in the x-ray powder diffraction spectrum is 2.22 Å. The salts KCI and KBr both have an FCC unit cell. If the ionic radii of CI, Br, and K' are 1.81, 1.96, and 1.33 A, respectively, what is the compound? Show your work. 4 5 8. The unit cell of a perovskite-based superconductor containing Cu, Ba, O and Hg is shown at right. It crystallizes in the tetragonal space group P 4/m m m a) What is the stoichiometry (formula unit) of this compound? atoms. the four copper atoms? possessed by the lattice point where the Ba atom at a, b, and c axes and the angles , , and in the unit cell? Cu b) Provide the unit cell coordinates of the copper c) What are the Miller indices for the plane defined by d) Provide two point group symmetry elements e) What is the relationship between the lengths of the O Hg cell coordinate (1/2, 1/2, 1/3) resides. 4. Moungi Bawendi and coworkers at the Massachusetts Institute of Technology 9 0 developed a synthesis of "quantum dot" colloids of CdSe via the following reaction:Explanation / Answer
2.
Formula of d spacing for FCC
dhkl = a/(h2+k2+l2)0.5
0.222 nm = a/(22+22+02)0.5
0.222 nm *(22+22+02)0.5 = a=1.776nm
In the FCC
(4R)2=a2+a2
R= 20.5 a
R=1.4142*1.776nm
So 4R=0.3535*4=2.5116nm
For KCl 4R=(0.133+0.181)*2=0.628nm
For KBr 4R=(0.133+0.196)*2=0.658nm
(4R)2=a2+a2
4R= 20.5 a
R=1.4142*1.776nm
So 4R=0.3535*4=2.5116nm
For KCl 4R=(0.133+0.181)*2=0.628nm
For KBr 4R=(0.133+0.196)*2=0.658nm
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