Crystal structure investigation of
Co0.5Ni0.5TiO3
Hmida SLIMANI*, Hicham ELMADIOUNE*, Rachid MAKHLOUF*
Prof. Youssef TAMRAOUI**, Prof. Bouchaib MANOUN**
*Students at Mohammed VI Polytechnic University Materials Science and Nano-engineering Department
** Professors at Mohammed VI Polytechnic University Materials Science and Nano-engineering Department
I.
Abstract:
In the present investigation the solid-state method was used to synthesis two materials NiTiO3 and Co0.5Ni0.5TiO3. The
XRD and UV-spectroscopy are used to identify lattice parameter of the two structure and optical parameter
respectively. For NiTiO3 we have simulate the XRD data using Rietveled refinement via Fullprof software, in order
to find lattice parameter: a=b=5.030728 A , c= 13.789178 A. Moreover, we calculate using the same method the
quantity of each phases present in our material and we obtained 93.61% for NiTiO 3 followed by TiO2 with a
percentage of 4.18% and the last one is NiO with fraction of 2.21%. the same treatment was done for the second phase
Co0.5Ni0.5TiO3. The parameter structure is a=b= 5.044982 Å, c= 13.839973 Å. Using FullProf program we find that
Co0.5Ni0.5TiO3 present (86.28%) and TiO2 is present with 13.72%. The crystalize size was evaluated from XRD data
and we found 154.55 nm for NiTiO3 and 1.77.90 nm for Co0.5Ni0.5TiO3. And using UV-spectroscopy of solid we have
evaluated all the gap energy for all the possible transition, allowed direct, allowed indirect, forbidden direct, forbidden
indirect, we have found 1.94,2.76,2.63 and 2.89 respectively.
Keywords: solid state, doping, DRX, ilmenite …
II.
Graphical abstract:
III.
Introduction:
New structure can come from existing materials, we
need just to put the right proportion and use the right
method to get them. One method is the solid-state
method, the oldest and most used method to produce
multicomponent solid material, a lot of structure can be
producing from completely different initial structure.
Perovskites and ilmenite structures with general
formula ABO3 (A=Pb, Ni, Fe, Co….) and (B=Ti,…) can
produced using initial reagent with different structure ,
in the perovskites structures a variation of the ionic
radius of B cation (rb) is permitted only to an extent
which is defined as the tolerance factor t, perovskites
structure forms when t lies between 0.8 and 1, for t
value smaller than 0.8 the ilmenite structure is formed .
Pressure disordering in the ilmenite structure may cause
its breakdown to slightly more dense corundum
structure , the perovskites and corundum phases are
seen to have higher entropies than the ilmenite , ilmenite
adopted a rhombohedral structure (R-3 space group)
which is stable at low temperature ,Nickel titanite
(NiTiO3) member of ilmenite family have attached
attracted great interest over the past few decades
because of the utilization of such materials in wide
range of application such as photocatalysis , sensor, fuel
cell, [1-5] , in NiTiO3 both Ni and Ti atoms prefer
octahedral coordination with alternating cation layers
occupied by Ni and Ti alone [6]
The literature about the properties study of ilmenite
materials influencing Co0.5Ni0.5TiO3 materials as a solid
solution has rarely been reported. In recent years,
NiTiO3, a widely known type of Ti-based ilmenite
(MTiO3), has become a key research topic in basic
physics and potential technology applications. Nickel
titanate is a trigonal crystal system with an ilmenite
structure. Ti and Ni atoms are spaced in the cationic
layer of octahedral coordination. NiTiO3 is a bright
candidate with a narrow band gap; it is an n-type
semiconductor with a band gap of approximately 2.18
eV [7,8].
In this manuscript, we report the synthesis, the optical
propriety, and Reitveld refinement of CoxNi1-xTiO3 by
solid state chemistry.
IV.
Materials and methods
a. Synthesis procedure / protocol
The synthesis of oxides by solid state reaction is one of
the most used methods in solid state chemistry and in
industries, thanks to its simplicity and its large-scale
production. We have used this method to elaborate our
perovskite compound Co0.5Ni0.5TiO3 following steps:
•
Reagents
Table 1:Reagents used in our study
Reagent
Formula
M (g/mol)
Titanium oxide
TiO2
79,86
Nickel oxide
NiO
74,69
Cobalt nitrate
hexahydrate
Co (NO3).6H2O
291,04
The reagents in the form of powders (Table1), are
weighed in stoichiometric quantities predicted by the
reaction.
•
Reaction
𝑻𝐢𝐎𝟐 + 𝐍𝐢𝐎 + 𝐂𝐨 (𝐍𝐎𝟑 ). 𝟔𝐇𝟐 𝐎 → 𝐂𝐨𝟎.𝟓 𝐍𝐢𝟎.𝟓 𝐓𝐢𝐎𝟑 + 𝐇𝟐 𝐎
Then we mixed them carefully by grinding in a mortar.
The obtaining homogeneous mixture composed of
small particles will then facilitate the kinetics of the
reaction, the mass obtained is 1.815 g. The powder is
then subjected to calcination which is a successive heat
treatment, firstly the temperature retained is 450°C for
1h, then temperature is raised to 650°C for 4h and by
solid phase diffusion phenomena the materials will react
until a single phase is obtained, the final mass obtained
is 1,760 g.
So, the degradation mass is:
md = 1.815 – 1.760 = 0.055 g
Since it consists of some impurities, we have been
reground in order to reduce the size of the grains and
increase its reactivity. The powder is then subjected
again to a heat treatment at high temperature which is
850°C for around 5h, then it increases to 1000 °C in
order to finally obtain the desired product.
b. Characterization techniques (XRD)
X-ray diffraction (XRD) is a technique for
characterizing crystallized materials, whether massive,
in the form of powder or deposits. In the laboratory, this
technique is mainly applied to inorganic materials:
minerals, metals, alloys, ceramics, etc.
The principle is as follows: The X-ray beams produced
by the tube are sent to the sample in which they are
deflected by the atoms. These diffracted beams interfere
with each other, leading to the production of an intense
signal in certain precise areas of space. It is this signal
which is collected by the detector and plotted in the
form of a curve (diffractogram) which presents peaks at
very specific angles of diffraction. The position of these
peaks is a real signature of the arrangement of atoms
inside a crystal (distance between atoms, between
intracrystalline planes). The empirical relationship
between the angles at which peaks are observed and the
distances between atomic planes is Bragg's law.
nλ=2d sin θ
c. Rietveld Method
The aim of Rietveld refinement is to find a set of powder
diffraction simulation parameters which lead to
optimum agreement between a simulated powder
diffraction pattern and experiment.
The refined parameters provide information about the
crystal structure and other properties of the powder
sample and instrument setup. The agreement between
simulation and experiment is quantified by a measure of
similarity.
Rietveld refinement are also used to refine parameters
affecting peak shapes and positions, such as profile
parameters, sample broadening, asymmetry parameters,
line shift corrections, cell parameters, and so on
The Rietveld program implemented in the Powder
Refinement tool is, for the most part, based on standard
algorithms employed in Rietveld refinement.
Robustness is achieved by ensuring that refineable
parameters remain within physically sensible ranges.
It is generally difficult to generalize refinement
strategies since every refinement has its own problems.
Nevertheless, it is useful for the novice to sequence the
refineable parameters. A typical refinement based on a
single-phase constant wavelength X-ray data set might
proceed as follows:
1.
2.
3.
4.
5.
6.
7.
8.
Scale and background
Lattice parameters
Peak shape
Fractional coordinates
Isotropic thermal parameters
Fractional occupancies
Anisotropic thermal parameters
Preferred orientation extinction and absorption
parameters
Before starting the refinement, we need several
information, unit cell dimension, Z, space group, atomic
coordinates, X-ray wavelength, approximate peak shape
parameters (pseudo-Voigt for XRD)
Therefore, a structural model has to be input into the
refinement in order to calculate structure factors, the
starting model may be found in a number of ways, a
known structure or isostructural analogue, calculated by
ab-initio techniques.
There are several Rietveld refinements packages, in our
study we use the FullProf package.
Refinement is normally continued until and acceptable
fit is obtained visually, or some convergence criteria
have been
pattern….)
V.
found
(R-pattern,
Results and data treatments
1. NiTiO3 structure:
a.
Overview about XRD Patterns
NiTiO3
B
30000
Intensity (a.u)
25000
20000
15000
10000
5000
0
20
30
40
50
60
70
2 Theta(°)
Figure 1: XRD spectra of NiTiO3
80
90
100
R-weighted
To have a general idea about this structure we have use
cycles of refinement, we got Bragg R-factor: 12.54 and
Highscore. Comparing our XRD with those of literature
RF-factor: 11.52 and steel some pics of the other phase
we found that we have extra peaks. It means that we
to fit. Then we added the second abundant phase TiO2
have other phases.
which we fitted using its structural parameters taken
from HighScore program. The refinement in this time
Table 2:Peaks of other phases present in our phase
reduce the the Bragg R-factor: 7.8 and RF-factor: 8.22
2 Theta
Phase
27.63
TiO2
36.28
37.41
54.33
TiO2
NiO
TiO2
of the first phase. However, the second’s phase factors
were inacceptable, the Bragg R-factor: 21.15 and RFfactor: 25.04. we have tried to change the model of TiO2
many times, but it was the best result we got. Finally,
we decide to add the last phase NiO, the same with TiO2
Frome the table below we believe that we have the
we extract its structural parameters from HighScore.
formation of side phase TiO2 and we steel have amount
The addition of this phase, all missing pics were
of NiO not reacted during the solid-state reaction. We
included within the refinement process. And the the
have obtained thin peaks in our XRD structure which
Bragg R-factor and RF-factor were dramatically
mean our product has a high crystallinity. Figure 1 show
reduced to:
the XRD spectra of NiTiO3.
b.
➢ Phase:
Crystal structure analysis (Rietveld refinement):
1
✓ Bragg R-factor: 2.121
The first thing we have done is much our structure with
✓ RF-factor: 2.232
other structure in literature using the high score
➢ Phase:
program. We found that we have 3 phases NiTiO3 which
2
✓ Bragg R-factor: 3.393
present 93.61% of the structure and TiO2 with a
✓ RF-factor: 4.606
percentage of 4.18% and the last one is NiO with
➢ Phase:
fraction of 2.21%.
3
✓ Bragg R-factor: 3.462
We start refining the abundant phase NiTiO3 which we
✓ RF-factor: 1.963
used its CIF file to facilitate the the task. After many
NiTiO3
Yobs
Ycalc
Yobs-Ycalc
Bragg_position
30000
25000
20000
Yobs
15000
10000
5000
0
-5000
-10000
20
30
40
50
60
70
80
90
100
110
! 2 Theta (deg.)
Figure 2: Plot of Rietveld refinement of NiTiO3. The upper symbols illustrate the observed data (red circles) and the calculated pattern (solid line).
The vertical markers show calculated positions of Bragg reflections. The lower curve is the difference diagram
c. Rietveld refinement conditions
Table 3:Details of Rietveld refinement conditions of the series NiTiO3
Composition
Symmetry
Space group
z
Lattice parameters
Volume
P-V function
Caglioti parameters
RF/RB
RP/Rwp
cRP/cRwp
d.
Phase1:NiTiO3
Phase2: TiO2
Phase 3: NiO
Hexagonal
R -3
1
a=b= 5.030728
c= 13.789178
302.225 A3
0.50000
U= 0.007790
V= -0.001655
W= 0.002201
Tetragonal
P 42/m n m
Cubic
F m -3 m
a=b= 4.593339
c= 2.959635
62.445 A3
0.50000
U= 0.019805
V= -0.007899
W= 0.003344
a=b=c= 4.177288
1.89/2.12
4.93/ 6.48
10.9/ 10.5
4.61/ 3.39
-------
1.96/ 3.46
-------
72.893 A3
0.50000
U= -0.009983
V= 0.011890
W= 0.000430
Structural parameters
Table 4: Refined structural parameters for NiTiO3 with R -3 as space group.
Ti
Ni
O
Site
NiTiO3
x
y
z
Biso
Occupancy
6c
0
0
0.14463
0.50000
1.00000
6c
0
0
0.35075
0.50000
1.00000
18f
0.31643
0.01831
0.24522
0.50000
3.00000
2. Co0.5Ni0.5TiO3 structure:
Table 5: Selected inter-atomic distances (Å) in the series NiTiO3
0.0
Composition
6c site with Coordination number = 6
2.0784
Ti—O1
1.8523
Ti—O2
1.9654
<Ti—O>
2.1245
Ni—O1
2.0585
Ni—O2
2.0915
< Ni—O1>
18f site with coordination number 4
2.0784
O1-- Ti
1.8523
O1-- Ti
2.1245
O1-- Ni
2.0585
O1-- Ni
2.0284
Average dis
Tables 4 and 5 represent the refined structural
parameters and inter atomic distance in the series
respectively for NiTiO3.
We can see clearly that the distance between O and Ni
is greater than the distance between O and Ti.
a.
Overview about XRD Patterns
The same thing we have done for the first structure. We
will use fullprof software to define the phases present in
our product
Table 6:Peaks of other phases present in our phase
2 Theta
Phase
27.57
TiO2
36.20
TiO2
41.26
TiO2
54.35
TiO2
56.65
TiO2
In this case we see that the only phase side phase
obtained is TiO2. And we don’t have NiO in the final
structure we can assume that it reacts totally in this case
because we have used half amount this time. Like the
first structure we have obtained thin peaks. Therefore,
our structure has a high crystallinity. Figure 3 show the
XRD spectra of the structure.
Co0.5Ni0.5TiO3
16000
14000
Intensity (a.u)
12000
10000
8000
6000
4000
2000
0
-2000
20
30
40
50
60
70
80
90
100
2 Theta (°)
Figure 3:XRD spectra of Co0.5Ni0.5TiO3
b.
Crystal structure analysis (Rietveld refinement):
Co0.5Ni0.5TiO3
20000
Yobs
Ycalc
Yobs-Ycalc
Bragg_position
Yobs
10000
0
10
20
30
40
50
60
70
80
90
100
110
! 2 Theta (deg.)
Figure 4:Plot of Rietveld refinement of Co0.5Ni0.5TiO3. The upper symbols illustrate the observed data (red circles) and the calculated
pattern (solid line). The vertical markers show calculated positions of Bragg reflections. The lower curve is the difference diagram
The main idea was to use the PCR file generated in the
undoped structure NiTiO3, but the model didn’t work
much and were not able to refine using this PCR file.
Therefor we start the refinement from the beginning this
time. The first thing we have done is analysing our
structure using High score software, in order to define
how many phases, present in this product. We found
that we have in parallel with NiTiO3 doped phase with
0.5 of Co we have another phase which correspond to
TiO2 phase. This explain why the PCR file of NiTiO3
does not work, in this product we do not have NiO phase
which could deform the refinement process. Using
FullProf program we refined firstly the abundant phase
Co0.5Ni0.5TiO3 (86.28%). And after many cycles of
refinements, we got a Bragg R-factor: 10.5 and RFfactor: 11.33
That we could not make it better because some pics
were not fitted (Figure 4). Then we add the second
phase TiO2 (13.72%) using structural parameters
obtained in HighScore. Finally, all pics were included
and well fitted in the refinement and we have reduced
the:
Phase1:
➢ Bragg R-factor: 1.941
➢ RF-factor: 3.517
Phase 2:
➢ Bragg R-factor to: 3.066
➢ RF-factor to: 3.659
c.
Rietveld refinement conditions
Table 7:Details of Rietveld refinement conditions of the series Co0.5Ni0.5TiO3
Composition
Symmetry
Space group
z
Lattice parameters
Phase 1: Co0.5Ni0.5TiO3
Hexagonal
R -3
1
a=b= 5.044982
c= 13.839973
305.060 A3
0.12379
U= 0.010088
V= -0.001821
W= 0.001887
2.94/ 1.92
5.77/ 7.52
14.2/ 13.1
Volume
P-V function
Caglioti parameters
d.
RF/RB
RP/Rwp
cRP/cRwp
Structural parameters
Phase 2: TiO2
Tetragonal
P 42/m n m
a=b= 4.593287
c= 2.959840
62.448 A3
0.12379
U= 0.000818
V= 0.001668
W= 0.001951
3.66/ 3.07
-------
Table 8:Refined structural parameters for NiTiO3 with R -3 as space group.
Ti
Ni
Co
O
Site
NiTiO3
6c
6c
6c
18f
x
y
z
Biso
Occupancy
0
0
0
0.31750
0
0
0
0.02060
0.14496
0.35200
0.35200
0.24490
1.15755
1.63431
1.63431
1.86482
1.00000
1.00000
1.00000
3.00000
Table 9:Selected inter-atomic distances (Å) in the series Co0.5Ni0.5TiO3
0.0
Composition
6c site with Coordination number = 6
2.0792 (32)
Ti—O1
2.0792 (39)
Ti—O1
2.0792 (29)
Ti—O1
1.8507 (25)
Ti—O2
1.8507 (34)
Ti—O2
1.8507 (40)
Ti—O2
1.9650
<Ti—O>
2.1464 (32)
Ni—O1
2.1464 (38)
Ni—O1
2.1464 (29)
Ni—O1
2.0663 (40)
Ni—O2
2.0663 (26)
Ni—O2
2.0663 (32)
Ni—O2
2.1064
< Ni—O1>
2.1464 (32)
Co—O1
2.1464 (38)
Co—O1
2.1464 (29)
Co—O1
2.0663 (40)
Co —O2
2.0663 (26)
Co —O2
2.0663 (32)
Co —O2
2.1064
< Co —O1>
18f site with coordination number 6
2.0792 (32)
O1-- Ti
1.8507 (25)
O1-- Ti
2.1464 (32)
O1-- Ni
2.0663 (40)
O1-- Ni
2.1464 (32)
O1—Co
2.0663 (40)
O1-- Co
2.0592
Average dis
e.
Crystallite size calculation:
The crystallite size was evaluated form XRD Data
using Scherer’s Formula:
𝐷𝑝 =
𝐾𝜆
𝐵𝑐𝑜𝑠(𝜃)
We have Select 4 pics for each compound we
summarize the result in the following table:
Compound
Peak position 2θ (°)
FWHM
size (°)
NiTiO3
Ni0.5Co0.5TiO3
f.
33.134361
0.064423
35.68793
0.055439
54.023376
0.06014
24.169256
0.049413
33.024391
0.055445
35.586544
0.04357
24.097744
0.047754
24.09758
0.047702
B
Dp Average
(nm)
154.55
177.90
Structure view:
Where, R is the diffuse reflectance and F(R) is called
the Kubelka-Munk function which is proportional to
absorption coefficients ‘A’.
The optical band gap energy was then estimated using
the onset of the absorption edge by Tauc plots [11].
The predominant mechanism of the band to band
transitions, which are responsible for the shape of the
absorption edge, was determined by investigation of the
dependence F(R) as a function of the incident photon
energy (hν). The relation between the absorption
coefficient and hν can be determined using Tauc's
relationship in the high absorption region [11,12]:
F ( R)h = A(h − Eg )n
Where,
F(R) is the linear absorption coefficient or the Kubelkamunk function,
υ= C/λ is the light frequency, with λ being the
wavelength (meter) and C is the speed of light =3.0×108
(meter/sec).
h = Planks constant = 6.626×10-34 Joules sec,
A is a constant depending on the transmittance
properties of Eg.
The index n is determined by the nature of the electron
transition during the absorption process. This index
determines the transition nature; it’s also called power
of probabilities. Four possible values which are 1/2, 2,
3/2 or 3 corresponding respectively to direct allowed,
indirect allowed, direct forbidden and indirect forbidden
types.
In order to determine optical band gap (Eg)
experimentally, [F(R)hν] n (n=1/2, 2, 3/2 or 3) versus
the photon energy (hν) can be plotted using the data
obtained from the optical absorption spectra. As a
result, and according to Tauc plot the straight line was
extrapolated to intercept (hν)-axis at [F(R)hν] ½ = 0
VI.
Optical measurement (band gap calculation):
Band gap Eg is a tunable property that is affected by
numerous parameters such as synthesis root and
thermodynamic conditions, surface morphology, crystal
structure, atomic substitution Ratio, and the degree of
distortion.The theory of Kubelka-Munk function was
proposed by P. Kubelka and F. Munk [9,10] to calculate
the Eg from the reflectance spectra, according to:
(1 − 𝑅)2
𝐹(𝑅) =
2𝑅
%R
0.3
0.2
0.1
200
300
400
500
600
700
wave length (nm)
Figure 5: Co0.5Ni0.5TiO3 UV/Vis Spectrum obtained in
Reflectance mode
800
Figure 8:(αhν)n (n=1/2, 2, 3/2 or 3) versus (hν) for the prepared material.
Fig.7 show the evolution of absorption coefficient (KM function) in the range of wavelength between 250
and 800 nm, where two absorption bands are clearly
identified at 400 and 600 nm.
6
K-M function F(R)
5
4
Fig.8 shows the plots of (αhν)
prepared material.
3
2
1
0
200
300
400
500
600
700
800
n
versus (hν) for the
We have determined the bandgap for our compound of
all the transition, we Summarize the result in the
following table.
wave length (nm)
Figure 6:UV-vis-near-IR Spectrum of Co0.5Ni0.5TiO3 sample,
showing the evolution of absorption coefficient (K-M function) in
the range of wavelength between 250 and 800 nm.
In Fig.6 we can see the reflectance spectra for our
sample, where two absorption bands are clearly
identified at 500 and 700 nm.
Type of Transition
Direct allowed
Indirect allowed
Direct forbidden
Indirect forbidden
Gap Energy (eV)
1.94
2.76
2.63
2.89
VII.
Conclusion
The MTiO3 has received an attention for their use in
application such as in electric field. During this work we
have applied the solid-state reaction to prepare Nickel
titanate and nickel cobalt titanate (Co0.5Ni0.5TiO3). the
two structure are treated the same way. To analyse our
product, we have used XRD to identify the crystallinity
of materials and the phases formed, and UVspectroscopy in order to measure the gap bond of each
structure.
The XRD analysis show that the NiTiO3 structure
contains two other phases TiO2 which was formed
during the heat treatment, and NiO which correspond to
the amount of reactant does not reacts. Those result was
confirmed by HighScore software. The second structure
(Co0.5Ni0.5TiO3) involves only one parasitic phase TiO2.
Both structures give XRD spectra with thin peaks.
Therefore, both are highly crystalline. Moreover, we
have used Rietveld refinement via Fullprof software in
order to find structural parameters of a material, and to
quantitatively examine the mixing ratio of each phase in
the material.
And as we have mentioned earlier those structures are
in electric field so it’s necessary to measure their band
gap using UV-spectroscopy of solid and we have found
1.94 eV for Co0.5Ni0.5 TiO3 which correspond to semiconductive materials
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