Effect of JahnTeller distortion on the lattice vibration frequencies of nickel
ferrite
C. M. Srivastava and T. T. Srinivasan
Citation: J. Appl. Phys. 53, 8148 (1982); doi: 10.1063/1.330276
View online: http://dx.doi.org/10.1063/1.330276
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Published by the American Institute of Physics.
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Effect of Jahn-Teller distortion on the lattice vibration
frequencies of nickel ferrite
C. M. Srivastava and T. T. Srinivasan
Department 0/ Physics. Indian Institute o/Technology. Bombay-400 076. India
The infrared spectra of Nil_,Cu,Fe,O. (x = 0, 0.1, 0.2) studied at room temperature in the range of 250-S00
em -I show two main bands. On adding copper to nickel ferrite, the center frequency of these two bands is
found to shift to lower energies. The force constants obtained using the center frequency have been observed
to increase linearly with the internuclear separation for both the octahedral and tetrahedral sites.
PACS numbers: 75.50.0g, 7S.90. + t, 7S.30.Er
INTRODUCTION
EXPERHIENTAL
The effect oi the substitution of a Jahn-Teller
Z
ion like Cu + on the properties of Ni-Zn ferrites has
shown [I,Z] interesting results. The lattice constant
is significantly reduced on 10% copper substitution.
On increasing the copper concentration to ZO% the
lattice constant increases but is smaller than pure
nickel ferrites. The curie temperature, Tc is unaffected [Z] by copper substitution upto ZO% copper
concentration. The M6ssbauer spectra of copper substituted NiZn ferrite show significant change compared
to those without copper substitution. The changes in
lattice constant and magnetic properties have been
attributed to the local distortion produced by the
Jahn-Teller ion and its effect on the crystal field
state of the NiZ+ ion. It has been assumed [1] that
Z
the local distortion created by the Cu + ion is
necessarily seen by the NiZ+ ions which are on equivalent crystallographic sites,
In view of these observations it was thought
desirable to investigate the effect of copper substitution on lattice vibrational frequencies. The
contraction is expected to increase the force constant,
Our results however show that both the force constants
ko and kt' related to the metal ions in the octahedral
and tetrahedral sites respectively decrease on 10%
copper substitution. The force constants have been
obtained from the infrared absorption data using the
analysis of Waldron [4]. Further increase in copper
concentration to ZO% show an increase in the values of
ko and kt due to the increase in lattice constant, 'a',
Waldron's result, however, show that on the expansion
of the lattice ko increases but k decreases. This is
t
concluded from his results on nickel and nickel-zinc
ferrite. On the substitution of 70% zinc in nickel
ferrite the lattice expands by 0.78% and his value of
ko shows an increase of about 6% over the nickel
ferrite and a decrease of 9% for k , In our case,
t
however, on 10% copper substitution the lattice
contracts by 0.4% [2] and ko and k both decrease by
t
6% and 8% respectively.
The increase in the force constant with the
increase in the inter nuclear distance agrees with
similar dependence observed in the oxides of transition
metals with 26 ~ Z ~ 29 [5].
8148
J. Appl. Phys. 53(11), November 1982
The samples with compositions Ni _ CU Fe 0
l x
Z4
x
[x = 0, 0.1 and 0,2] were prepared using the normal
conventional ceramic technique. All the samples were
found to have densities higher than 97% of their X-ray
density. The x-ray analysis showed single phase and
spinel structure. The cell constants are given in
Table-I.
To have uniform dispersion in the KBr pellet the
ferrite samples are powdered to 100 mesh size and mixed
with KBr in the ratio 1:250 by weight. The mixed
powder is then placed in a cylindrical die of 20 mm dia
and pressed at 30 TSI. The clean discs of approximately 1 mm thickness are obtained.
I
The spectra in the range of 250-800 cm- are
recorded at room temperature on a SP ZOOO Infrared
Spectrometer [P1E UNICHE~I MAKE]. These are shown in
Fig.l.
DISCUSSION
From Fig.l it is observed that the spectra of x=O
and x=0.2 are similar and have narrow bands while that
of x=O.1 has broader bands. Moreover, the shift in the
centre frequency on copper substitution is larger for
10% compared to 20% copper substitution. From Table-I
it is observed that the difference between the lattice
parameters of X=O and x=0.2 is small compared to X=O
and x=O.I. The larger change in 'a' on 10% copper
substitution is responsible for larger shift of the
centre frequency and also for the broadening of the
bands. From the lattice parameters the internuclear
separation between metal and oxygen ions has been
calculated for the octahedral and tetrahedral site.
The variation of k and k with r is shown in Fig.2.
o
Both k
o
and k
t
t
e
are found to increase linearly with reo
This is unexpected since the increase in re should
normally lead to decrease in ko and kt • However, a
similar dependence of ko with r e has been observed for
transition metal oxides within the range 26 ~ Z , 29
[5J. This type of dependence is attributed to the
fact that oxygen can form, under favourable ca:es,
stronger bonds with metal ions at even larger lnternuclear separations.
0021-8979/82/118148-03$02.40
© 1982 American Institute of Physics
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8148
80
80
60
60
!:
'0
~
w
o
20
20
800
1000
__
1000
800
-
600
'00
600
WAVE
NUMBER
250
'00
(C",')
250
WAVE NUMBER lem· l )
~--------------------------,8Q
80
601
60
>in
~
'0
1000
800
- - WAVE
Fig.l.
600
'00
z
w
<:>
250
1000
800
NUMBER I em-I)
'00
600
WAVE
250
NUMBER Ie m' l )
Infrared Spectra for Nil_~cu~Fe204 (x=O, 0.1
and 0.2) and ZnFe 204 •
The spectrum of ZnFe Z04 given in Fig.l, shows one
additional absorption peak at about 338 cm- l
This is
a common feature of most normal spinels which show
three bonds while inverse spinels show only two. The
origin of the third band in normal spinels has not yet
been explained.
fe(OBlxl0 8 cm
2.07
f
..
~
2.3
GO
""'"
'"S!
-0
2.2
2. I
2.08
2.09
1·08
-If•
...E
1.06 '-
...
C
'.01.
.On ~ubstituting copper in nickel ferrite, NiFe 0
a shIft In the lattice vibrational frequencies has 2 4'
b:en observed. From this shift it has been found that
t e force con~tants for the ions on the octahedral and
tetrah~ral sItes depend linearly on the internuclear
separa hons.
8149
J. Appl- Phys. Vol- 53, No. 11, November 1982
II>
2
\.02
0
-"
.><
CONCLUSION
..."""
\.79
1.80
fe ( OA) • 10 8 cm
Fig.2.
,·81
Variation of force constants ko and kt with
internuclear separation for Nil_xCuxFe204
(x=O, 0.1 and 0.2).
C. M. Srivastava and T. T. Srinivasan
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8149
TABLE I
v
a
x
vI
cm -1
cm -1
(A)
0
608
417
0.1
585
0.2
600
2
REFERENCES
k
x 10- 5
0
k
t
x 10- 5
0
C.M. Srivastava, M.J. Patni, G. Srinivasan and
T.T. Srinivasan, Bull. Mat. Sci., ~, 225 (1981).
dynes/cm
dynes/cm
2.
C.M. Srivastava, M.J. Patni and T.T. Srinivasan,
J. Appl. Phys. ~, 2107 (1982).
8.335
1.059
2.342
3.
405
8.301
1.001
2.163
C.M. Srivastava, S.N. Shringi, M.J. Patoi and
S.M. Joglekar, Nuclear Physics and Solid State
Physics Symposium (India) 24C, 457 (1981).
410
8.323
1.027
2.282
4.
R.D. Waldron, Phys. Rev. 99, 1727 (1955).
5.
G. Herzbag, 'Molecular spectra and Molecular
structure I spectra of Diatomic Molecules',
second edition, D. Van Nostrand Co. (1950) p458.
Variation of lattice parameter, force constants, ko'
k and lattice vibration frequencies vI' v 2 for
t
Ni1_xCuxFe204 [x=O, 0.1 and 0.2).
8150
I.
J. Appl. Phys. Vol. 53. No. 11. November 1982
c. M. Srivastava and T. T. Srinivasan
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8150