Q.1
Gold crystallizes in a face centered cubic unit cell. If the edge length is a.
Calculate the closest distance between the gold atom and an impurity atom if it occupies a) a
tetrahedral void b) an octahedral void
without any change in volume of he unit cell.
ANSWER:
- a) closest distance if an impurity occupies a tetrahedral void: - √3/4 a
b)
Closest distance if an impurity occupies an octahedral void: - a/2
Q.2
a) Spinel is an important class of oxides consisting of two types of metal ions
with the oxide ions arranged in ccp
pattern. The normal spinel has one- eight of the tetrahedral voids occupied by
one type of metal ion and one half of the octahedral holes occupied by another
type of metal ion . such a spinel is formed by Zn+2, Al+3 and
O-2 with Zn+2 in tetrahedral holes. Give the formula of
the spinel.
b)
if all species in above question touch each other, determine the
fraction of he volume occupied by ions in the unit cell.
ANSWER
:- a) ZnAl2O4 b) 0.77
Q.3
a strong current of trivalent gaseous boron passed through a germanium crystal
decrease the density of the crystal due to part replacement of germanium by
borone and due to interstitial vacancies created by missing Ge atoms. In one
such experiment, one gram of germanium istaken and theboron atoms are found to
be 150 ppm by weight, when the density of the germanium crystal decreases by 4
% Calculate the percentage of missing vacancies due to germanium, which are
filled up by boron atoms
ANSWER
:- 2.376%
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