Materials Sciences and Applications, 2012, 3, 538-542
http://dx.doi.org/10.4236/msa.2012.38076 Published Online August 2012 (http://www.SciRP.org/journal/msa)
Structural and Optical Properties of Znx−1MgxO
Ceramic Composites
Zayani Jaafar Othman, Adel Matoussi
Laboratory of Composite Ceramic and Polymer Materials, Scientific Faculty of Sfax, Sfax, Tunisia.
Received May 4th, 2012; revised June 5th, 2012; accepted July 6th, 2012
ABSTRACT
In the present work, we investigate the structural and optical properties of Znx−1MgxO composites prepared by the
standard sintering method at 1200˚C during 24 hours and doped with different percentages of magnesium x between 0%
and 40%. For this purpose, we have used the X-ray diffraction (XRD) and the atomic force microscopy (AFM) to study
the effect of the magnesium’s proportion on the crystalline and morphology proprieties of the obtained samples. XRD
analysis showed that all films are polycrystalline with a hexagonal wurtzite structure, with an orientation of the grains
according to directions (0002) and (10-10). The AFM characterisation show that the degree of surface roughness (RMS)
increases with the increasing of MgO content. Optical properties of the ceramics were investigated by Absorbance and
Reflectance measurements at room temperature in the wavelength range 200 - 2400 nm. Optical band gap energies (Eg)
were determined. Further cathodoluminescence and dielectric measurements would be carried out to study the influence
of MgO doping on the dielectric and luminescent properties of the ZnMgO ceramics.
Keywords: Znx−1MgxO Composites; X-Ray Diffraction; AFM; Optical Properties
1. Introduction
The growth and characterization of II-VI semiconductor
ZnO based alloys (including MgZnO, CdZnO, and
MnZnO) have been becoming a more and more active
research field in recent years. The research interests on
ZnO have been encouraged by the industrial and techno-
logical demands for the new generation of opto-elec-
tronic devices, because of its wide band gap (3.4 eV at
300 K) and large exciton binding energy (60 meV) [1].
ZnO is a promising candidate material for advanced de-
vices applications due to the above-mentioned character-
istics and unique combination of its physical properties
optical, electrical, magnetic, piezoelectric, and ferroelec-
tric. These characteristics are used in a wide range of
applications such as solar cells [2], transparent conduct-
ing films, chemical sensors [3,4], varistors [5,6], light-
emitting diodes [7], laser diodes [8], etc. Furthermore,
ZnO is a reliable candidate operated for high temperature
electronic devices that can be surely used in harsh envi-
ronments [9,10]. ZnO samples have been synthesized by
a variety of processes, including vapor deposition [11],
pulsed laser deposition [12], molecular beam epitaxy [13],
metal organic chemical vapour deposition (MOCVD)
[14], sputtering [15], electron beam evaporation [16],
spray pyrolysis [17,18], sol-gel processing [19].
In this work, we interested to preparation and charac-
terization of Znx−1MgxO bulk ceramics to study the in-
fluence of the MgO content on the structural, morpho-
logical and optical properties of the ZnMgO composites
for the potential applications in the new optoelectronic
devices.
2. Experimental Procedure
Znx−1MgxO composites were prepared by conventional
solid state reaction method using a mixture of metallic
oxides ZnO and MgO purchased by the GmbH Aldrich
Company. The weight content of MgO (x = 0% - 40%)
was added to pure ZnO powder (99.99%) and milled in
an agate which calcined at temperature of 500˚C for 3
hours in air ambient furnace. The ZnO-MgO powders
were pressed into pellets (of 1.5 mm in thickness and 8
mm in diameter) and sintered at a high temperature
1200˚C for 24 hrs with heating rate of 10˚C/min. Pellets
were then cooled slowly to room temperature. X-ray dif-
fraction (XRD) with Cu-Kα radiation wavelength of
0.15406 nm was used to determine the crystal structure
of ZnMgO ceramics in the scan range 2θ = 20˚ - 60˚.
The surface morphology was analysed by Atomic
force microscopy (AFM). Optical properties of the
ZnMgO pellets were examined in the wavelength range
200 - 1800 nm by using the UV-VIS-NIR spectropho-
tometer (SHIMADZV UV-3101PC).

Structural and Optical Properties of Znx−1MgxO Ceramic Composites 539
3. Results and Discussions
3.1. Structural and Morphological Properties
Figure 1 shows the XRD patterns of Znx−1MgxO pellets
for different additive content. All the composites exhibit
a polycrystalline hexagonal structure marked by the ap-
pearance of peaks corresponding to wurtzite reflections
planes (10.0), (00.2), (10.1), (10.2) and (11.0). As the
weigh content (x%) is increased, it observed at 36.7˚ and
42.7˚ the reflections planes (111) and (200) for cubic
phase of MgO. As shown in the inset (Figure 1), the in-
tensity of (0002) XRD peak decreases and shifts towards
high 2θ angles as the MgO content increases from 0% to
40%. This result suggests that the lattice parameter along
the c-axis decreases indicating a compressive strain [20].
The grain sizes, lattice parameters, strains and residual
stress values were calculated and presented in the Table
1.
The texture coefficient of oriented crystallites was
calculated using the well-known formula reported in Ref.
[21]. It is found that the highest TC values (greater than
1.2) correspond to (00.2) and (10.1) planes which con-
tribute about oriented grains of 42% and 27% respec-
tively. The average grain sizes of the films are calculated
from (0002) diffraction peak using the Scherrer’s equa-
tion [22]. It can be seen that grain size decreases from
109 nm to 55 nm as x (wt%) varied from 0 to 40. This
behaviour is observed in previous works [23,24].
Figure 2 shows the variation of lattice strain and re-
sidual stress in Znx−1MgxO ceramic composites with ad-
dition of MgO content. It must be noticed that the sample
doped with 10% of MgO has larger strain and stress val-
ues. The residual stresses σzz are compressive which tend
to decrease from 1016 MPa to 834 MPa when MgO ad-
ditive content increased from 10% to 40% respectively.
Figure 3 shows AFM images of ZnMgO pellets. The
surface morphology is covered by randomly distributed
islands with heights in the range 0.3 µm - 1.28 µm. With
increasing MgO content, the surface rms roughness in-
creases from 67.3 nm, 102.45 nm to 252.54 nm as x va-
ried from 0%, 20% and 40% respectively. From the
above results, it is seen clearly an improvement of the
microstructure and the crystalline quality of the ZnMgO
composite as the doping content increased.
3.2. Optical Properties
In this part, the absorption and reflectance spectra of
Znx−1MgxO composites were measured at room tempera-
ture using UV-VIS-NIR spectrophotometer. Figure 4
shows the absorbance of the composites with different
MgO contents. The optical transmittance does not meas-
ured because the studied pellets are very thicker of about
1.5 mm. In UV wavelength region, the average absorb-
ance decreases approximately from 42% to 22% when
MgO content increases from 0% to 30%.
For composition x = 40%, the optical absorbance in-
creased to 51%. One can noticed that all the ZnMgO
samples tend to more reflect the visible lights. In the ZnO
absorption spectrum, it appears prominent peak at 374.8
nm attributed to the exciton transition, indicating thus a
Figure 1. XRD patterns of Znx−1MgxO composite.
Table 1. The grain sizes, texture coefficient (TC), lattice parameters, lattice strain and residual stress values of Znx−1MgxO
composites.
MgO (wt%) a (Å) c (Å) TC (00.2) χ (%) (00.2)TC (10.0) χ (%) (10.0)D (nm) Εzz (×10−3) Σzz (GPa)
0 3.247 5.183 2.045 40.9 1.374 27.4 108.94 −1.55 0.355
10 3.249 5.173 2.146 43.3 1.207 24.1 83.43 −4.48 1.016
20 3.252 5.181 1.968 39.3 1.318 26.3 69.88 −4.41 1.002
30 3.251 5.186 2.022 40.4 1.276 25.5 50.49 −4.42 1.003
40 3.250 5.182 2.106 42.1 1.242 24.8 55.72 −3.67 0.834

Structural and Optical Properties of Znx−1MgxO Ceramic Composites 540
Figure 2. Variation of lattice strain and residual stress in
Znx−1MgxO composites with MgO content.
high optical quality of the material.
Figure 5 shows the plots (αhν)2 versus photon energy
for all samples. From these curves, we have determined
the band gap energy Eg using the following relationship
[25]:

1/2
hBhEg   
where B, α, hν are constant, absorption coefficient and
energy photon respectively. Determined Eg values are
given in the inset (see Figure 5).
For MgO composition varied from x = 0% to 30%, we
have observed a decrease in Eg value from 3.42 eV to
3.25 eV respectively. This is consistent with highly
doped ZnO samples [26,27]. But, for weight concentra-
tion x = 40%, the band gap of MgO-ZnO system reaches
a value about 3.71 eV.
This increase can be attributed to the Burstein-Moss
effect and/or to the formation of hexagonal ZnMgO alloy
phase [28-32]. Chunming Jin [32] and Ohtomo [28] have
synthesized single hexagonal MgxZn1−xO thin films with
x up to 0.36 where its band gap tuned from 3.36 to 4.12
eV. In our case, the observed decrease of Eg can be ex-
plained to low solubility of MgO in ZnO [33] and cubic
phase MgO segregation as confirmed by XRD analysis.
In future, we plan to determine the composition limit
(xc%) above it occurs changes on the structure and opti-
cal properties of ZnO-MgO composites. Cathodolumi-
nescence and dielectric measurements would be carried
out to study the influence of MgO doping on the dielec-
tric and luminescent properties of the ZnMgO ceramics.
4. Conclusion
Znx−1MgxO composites prepared were deposited by stan-
dard sintering method at 1200˚C. The effects of MgO
content on the structural, morphological and optical
properties of Znx−1MgxO composites were investigated.
All the deposited composites are polycrystalline with
(a)
(b)
(c)
Figure 3. 3D AFM images obtained for Znx−1MgxO compo-
sites (a) x = 0%; (b) x = 20% and (c) x = 40%.

Structural and Optical Properties of Znx−1MgxO Ceramic Composites 541
Figure 4. Absorbance spectra of Znx−1MgxO pellets meas-
ured at room temperature.
Figure 5. Plots of (αhυ)2 vs. photon energy of Znx−1MgxO
composites.
hexagonal wurtzite structure. XRD revealed the inclusion
of cubic MgO phase as the doping content increased up
40%. AFM analyses show rms roughness in the range
67.3 - 252.54 nm for Znx−1MgxO (x = 0 - 0.4) ceramics.
Optical properties of the ceramics were investigated by
Absorbance and Reflectance measurements at room temp-
erature in the wavelength range 200 - 2400 nm. We ob-
served decrease in the band gap Eg for concentrations x ≤
0.3 and increases when x = 0.4. This increase in Eg can
be attributed to the formation of ZnMgO alloy structure.
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