Non - Stoichiometric Defects Video Lecture - JEE

hello friends this video in solid states
part 21 is brought to you by exam Viacom
no more fear from exam the next type of
point defect I will be discussing is the
impurity defect so here some foreign
elements are involved in case of
impurity vehicles talk about impure that
in some foreign elements are what
elements involved example is you have
this sodium chloride in the molten state
you melt it and then add SR cl2 little
amount in NaCl mold in this is very
little amount so what will happen is
this SR will be nothing but s r2 plus
and Cl minus and C elements in this NaCl
is nothing but any plus NZ elements
there will be in the molten State so
what will happen is to maintain a
neutral D again if you add 1 SR right 1
SR is equivalent to 2 any plus as far as
charge concerned because it has two
positive charge na has one positive
shots or to any will give to position so
if one of this na is replaced with SR
the month space will be vacant to
maintain neutral right because 1 SR will
occupy will keep 2 na out so 2 na is
kicked out and 1 SR is occupying the
space M 1 is vacant this is my SR and
this is a vacant space ok trying to
understand whenever I say so - na is
kicked out from this crystal
and one SR is capable enough to provide
the similar amount of charge but one SR
cannot buy only one space one space will
be vacant correct
so in this cationic vacancy is created
and if you observe it the number of
Catania vacancy is created is nothing
but the number of SR ions added right
so one SR will create one tonic you can
see this is - you maintain your ad
similar in case of cdcl - and agcl so
you take AG CL and you add CD CL so in C
D has plus two charge so one CD will
kick out to silver by one silver place
and once the place will be empty so you
get this kind of defect this is called
impurity defect that we have for foreign
elements and foreign elements are
creating problems so in this case sodium
chlorite SR is creating problem it is
kicking - spooning out occupying one
space and one space is vacant let us
talk about non stoichiometry in case of
non stoichiometric defect it disturbs it
disturbs stoichiometry of the crystal in
fact a large number of non
stoichiometric defect exist even in fact
I mean to say the large number of
crystals exist which has non
stoichiometry decay in the organic
inorganic world they are two types
mainly metal excess and metal deficiency
so let us understand the metal exes like
the metal Texas also is by two ways one
is one is due to an ionic vacancy
and the next is due to extra cation in
interstitial site or ad so it's
understand the first one due to an eye
an ionic vacancy see alkyl halides like
sodium chloride potassium chloride so
that they show this de Becque so when
you heat this sodium right example you
take the sodium chloride and when you
heat this with sodium vapors you heat
this with sodium vapors start on sodium
vapors will come out right here will be
here nearby here now what happens is now
sodium vapors are deposited on the
surface correct just to avoid confusion
I am drawing only two sodium vapors
crystals
now this chlorine the green ones
chlorine will come out to the surface
and it will react with any so reaction
something like this CL minus will come
out will react with na so what will
happen so in this the moment will react
it will becomes NaCl and electron will
come off why because sodium will become
an a plus because sodium was more happy
to become an A plus there is more stable
and electron will come correct and this
chlorine came out of the surface so who
will occupy the space of this the
electron will occupy the space of this
example you see here so from this place
when chlorine came out when chlorine
came out there is a chlorine here see
there was a chlorine here this chlorine
came out and this chlorine reaction of
the sodium here it forms NaCl and
electron is extra and this electron took
this place of this chlorine this this
particle I can see that is site correct
so cl- diffuse to the surface
combined with na+ to form an ECL the
electron is lost as I showed you this is
the relay solectron diffused that with
the crystal and occupy the anionic site
knob you see crystal has now less sodium
because sodium went out now so the
chlorine went out so it has more excess
sodium close this by the chlorine this
was a chlorine here chlorine went out it
has excess sodium to dance excess sodium
but it has electron also correct and
this an onyx ID occupied by electron is
called F Center this is called lady kept
center at center size we have Centro
sure this anionic side is called F
centers F is far been Zinta that means
color because this imparts color example
in this case NaCl will get a yellow
color and why this gives color C we have
seen a Bohr model also this electrons
can easily be excited when you some
charge clicked awesome energy to it the
electrons will jump it will come back in
Adam and and then it will release energy
right it will it will release some color
see in think I was there when light
falls on this electron it jumps and then
it comes back on its own state when it
comes back on its own state release
color that's why it gives a yellow color
right same thing X in you take licl you
take licl and you put excess of a lie
right la vapor same thing will happen
right CL minus will come out and you get
this electron Center F centers and if
this you get pink color
so the la cycle becomes less infrared
becomes pain
same thing you would take potassium
chloride and again you have to heat this
with lot of potassium it will boil it
color here also you get X into F Center
correct so sodium chloride you got
yellow color with potassium chloride or
red you get pink and worker the next
type of defect as I told one do you do
extra cations in the interstitial site
so here we get the defect you do extra
cations in the interstitial example zinc
oxide is one example zinc oxide this is
white in color correct at room
temperature so when you heat this it
forms e in to class oxygen and electrons
this oxygen is gas it will go up now is
excess of zinc so what will happen is
this jink it will move to some interest
issues i and the electron will also move
to some neighboring site somewhere so
with this if you see it will have excess
of zinc the formula of Jed and O will
become 0 1 plus x something because this
has more of zinc not correct and with
this it gives a yellow color this is
yellow that is a good example of metal
exist effect where you have extra
cations in the interstitial site
now let's talk about metal deficient
defect this is Jenny shown by FeO
because fu is found in this form Fe 0.95
oh there's the defection of metal here
so what happens is generally if you see
here this is Fe 2 plus no.2 - correct
but if I have Fe 3 plus in fact two of
Fe 3 plus this is equivalent to if we do
plus Fe 2 plus and I could do this I'm
saying is right so 2 Fe 3 plus is
equivalent to 3 of AP 2 plus PI because
the net charge here is 6 and then charge
here is 6 so if I have 2 Fe 3 plus going
through the system that will kick out 3
Fe 2 plus let's suppose 3 Fe 2 plus is
Kito but they are good by only 2 space
mass this is vacant right and thus will
create metal deficient depend hope you
understand see Fe 3 plus 1 F 2 F III
plus can easily pick out 3 Fe 2 plus
correct so 2 Fe 3 plus can handle 3 or
Fe 2 plus baton charge so these two of
these will kick out 3 Fe 2 plus the one
in the blue and they'll avoid created
here
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