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MgO Effect on The Dielectric Properties of BaTiO3 
 

Samira Boumous 
Laboratory of Electrical Engineering and 
Renewable Energy, Mohamed Cherif 

Messaidia University, Souk Ahras, Algeria 
boumous@yahoo.fr 

Saad Belkhiat 
Laboratory DACHR, 

Ferhat Abbas Setif University 1, 
Setif, Algeria 

belsa_set@yahoo.fr 

Faicel Kharchouche 
Laboratory DACHR, 

Ferhat Abbas Setif University 1, 
Setif, Algeria 

Kharchouche.electro@yahoo.fr 
 

 

Abstract—The dielectric properties of barium titanate as 
functions of the MgO addition in various rates are investigated in 
this paper. The ceramics were prepared by conventional 
methods. X-ray diffraction, scanning electron microscopy and 
energy dispersive spectrometry, were applied to determine the 
structure and microstructure of the studied material. Phases 
MgO, TiO and TiO2, have been detected. Decrease of the grain 
size with increasing MgO content was observed. Measurements of 
εr, tgδ and resistance have been performed at temperatures 
ranging from 300C to 4000C. The electric permittivity (εr) showed 
a considerable decrease with increasing MgO concentration. 
Additionally, for low MgO concentration (10≤≤≤≤mol.% MgO) a 
shift of the dielectric loss peak (tgδm) towards low temperatures 
was observed. When the MgO content was ≥15mol.% MgO the 
tgδm moved into higher temperatures. The obtained results 
indicate that the substitution of Mg2+ ions in B-site ions (Ti4+) had 
a significant influence on the values of εr, tgδ and the resistance 
increase of the ceramics. 

Keywords-BaTiO3; MgO-doped BaTiO3; thermistors PTC; 

dielectric properties; electric permittivity 

I. INTRODUCTION  

Barium titanate (BaTiO3) is considered one of the most 
promising systems for applications in electro-optic devices, 
memory devices, temperature sensors, time delay circuits, 
current limiters, current stabilizers and capacitors [1]. BaTiO3 
is used as doping in other electrical engineering applications 
such as varistors [2] and in polymer composites like cable 
insulation sheaths [3, 4]. The dielectric and ferroelectric 
properties of BaTiO3 can be efficiently controlled by dopant 
addition. BaTiO3 is used in electric devices manufactured to 
work at temperatures less than its Curie temperature 
(Tc=120°C). In devices functioning at a temperature other than 
120°C, it is mixed with other materials such as Mg, PbTiO3 
(PT), Zr oxide, and other oxides, in order to shift Tc, above or 
under 120°C [5-11]. Pure BaTiO3 exhibits very high electric 
permittivity, since it has positive -temperature-coefficient 
resistivity (PTCR) above the Curie temperature [12, 13]. This 
phenomenon was considered as a consequence of the double 
Schottky barrier, formed at the grain boundaries and of the 
strong temperature dependence [14]. The PTCR phenomenon 
of doped BaTiO3, has been explained in [13, 15]. It has been 
concluded that the PTCR effect is caused by defect distribution 
in the samples. The effects of sintering conditions have been 
investigated in [11, 13, 16-19].  

BaTiO3, as additive in a varistor based ZnO, reduced the 
grain growth of ZnO as a function of the content of BaTiO3. It 
is found that an excess of 9.6wt% BaTiO3 leads to the BaTiO3 
phase segregation on the surface of the sample [2]. MgO-doped 
BaTiO3 has been less studied. MgO is very often added at small 
amounts, less than 3mol.%. This MgO ratio is generally used in 
multi-component BaTiO3-based ceramics, as high temperature 
capacitor in order to improve their temperature stability. MgO 
as an aliovalent in BaTiO3 plays a decisive role in achieving 
ultra-broad temperature stability [20-23]. The effect of the 
aliovalent dopant on the bulk electrical conductivity is strongly 
dependent on its substitution site in the BaTiO3 perovskite 
structure. Site replacement in the crystal lattice mainly depends 
on the dopant’s ionic radius [8, 10, 13].  For small ions, with 
ionic radius r≤0.09nm, dopants preferentially occupy the Ti 
site. For intermediate ions, with 0.09nm<r<0.099nm, dopants 
can substitute either Ti or Ba depending on dopant 
concentration, sintering conditions and Ba/Ti molar ratio. For 
larger ions, with r≥0.099nm, dopants preferentially occupy the 
Ba sites. In [21-22], the solid solution between MgO (content 
<1.5%) and BaTiO3 presents a XRD pattern, characteristic only 
of a single phase structure (BTO).This implies that Mg2+ ions 
have entered the unit cell maintaining the perovskite structure 
of solid solution. MgO phase in addition to the BTO phase, is 
detected for Mg contents, greater than 1.5% [21]. 

Electro-conductive composite ceramics are composed of an 
independent phase, of conglomerates and a continuous phase 
connecting mutually the independent phase of conglomerates. 
They are composed of an independent phase of conglomerates 
(50%-98% by weight) and of a continuous phase (2%-50% by 
weight) [24]. These ceramics can exhibit stable electro 
conductivity-temperature characteristics. They can be excellent 
in thermal shock resistance, in mechanical strength, and in 
chemical resistance. Concerning MgO-doped BaTiO3 
composite, only a few studies have been made [25]. In this 
paper, 5mol.%, 10mol.%, 15mol.%, 20mol.%, 30mol.%, and 
50mol.% MgO-doped BaTiO3 have been studied. The study 
aims to modify the BT-based materials characteristics such as 
Tc, electric permittivity and broaden the maxima peak. 
Sintering effect, microstructural evolution and incorporation 
degree of Mg into lattices (BaTiO3) have been discussed as 
functions of the MgO content. Electric permittivity and 
resistance have been measured in temperatures ranging from 
20°C to 400°C. 

Corresponding author: Samira Boumous



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II. EXPERIMENTAL PROCEDURE 

High-purity commercial powder BaTiO3 (code 01-081-
2200), obtained from ALFA AESAR, was used as starting 
material with 70nm grain size. Using a conventional ceramic 
procedure, BaTiO3 based varistor samples, doped with various 
contents of MgO (0, 5, 10, 15, 20, 30, 50mol.%.) were 
prepared. These samples are termed as BTM0, BTM5, BTM10, 
BTM15, BTM20, BTM30 and BTM50 respectively. Reagent 
grade oxides were mixed and homogenized in absolute ethanol 
media for 2 hours by planetary high-energy ball milling in a 
polyethylene bowl with zirconia balls. The slurry has been 
dried and sieved through a 200 mesh screen to produce 
granules without binder. The obtained powder was calcined at 
1150°C for two hours in air at heating and cooling rates of 
5°C/min. After drying and granulating with polyvinyl alcohol 
(PVA 4wt%) granules were uniaxially pressed into pellets 
under 20MPa and then CIPed at 200MPa. The pellets were 
placed in an alumina crucible and sintered at 1250°C for 2h in 
air at heating and cooling rates of 5°C/min, and silvered on 
both sides for electrical measurements. Silver electrodes were 
deposited by screen printing on each face. The sintered samples 
were all lapped and polished to be 1.0mm thick. The final 
samples had about 8mm i diameter and 1.0mm thickness. The 
samples were characterized by X-ray diffraction (XRD) using 
an automated diffractometer, Phillips PW-1710 type, coupled 
to a copper anode X-Ray tube. The microstructure of the 
samples was characterized by scanning electron microscopy 
(SEM type Hitachi-S2150) equipped with energy dispersive X-
ray (EDX) spectrometer for elemental analysis. Dielectric 
measurements were carried out with the use of an impedance 
analyzer RLC (Wayne Kerr 6420). The measurements have 
been performed from room temperature up to 400°C, at a 
heating rate of 3°C/min. εr, tgδ and resistance were measured. 
Under an alternate electric field, the electric permittivity of the 
material can be expressed by a complex permittivity such 
ε=ε΄(ω)–jε΄΄(ω). The dielectric loss tangent is defined as 
tgδ=ε΄΄/ε΄. In the following, we use the simplified notation εr 
and we will speak simply of permittivity to denote the real part 
of relative permittivity ε΄(ω). 

 

 
Fig. 1.  SEM image of the commercial BaTiO3 powder 

III. RESULTS AND DISCUSSION 

Commercial powder (BaTiO3) was used. It is composed of 
a very small agglomeration, whereas the grains were very fine, 

of the order of 70nm. Figure 1 shows a SEM image of the 
commercial BaTiO3 powder. We can see grain sizes smaller 
than one micrometer. In order to analyze the effect of MgO 
content on the microstructure and grain sizes, the samples have 
been characterized by SEM and XRD. Figure 2 shows the SEM 
images and EDX spectra of samples BTM0, BTM5 and 
BTM10 sintered at 1250°C. We can see in Figure 2(a) that the 
grain sizes of BaTiO3, are larger in comparison with the ones of 
the same sample before sintering (Figure 1). They are larger 
than 1µm, while some are even larger than 10µm. The bimodal 
microstructure of fine and large matrix grains can be attributed 
to the temperature effect, as in the case of ZnO [2] and to 
presence of titanium oxide. The EDX spectrum characteristic 
of BTM0 (Figure 3(a)) indicates that, there are 60.30atom% of 
oxygen, 20.77atom% of Ti and 18.84atom% of Ba. 

 

(a) 

 

(b) 

 

(c) 

 

Fig. 2.  SEM image of MgO-doped BaTiO3 after sintering at 1250°C (a) 
BTM0, (b) BTM5, (c) BTM10 

The grain size of BTM0 (pure) has increased under the 
temperature effect. Figures 2(b) and 3(b) show the morphology 



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and EDX spectrum of the sample BTM5. We can see that the 
grains are smaller. The surface morphology revealed some 
clear grain shapes. Figure 2(b) is brighter than Figure 2(a). We 
can see some bright domains, characteristics of MgO. The 
incorporation of MgO particles into the matrix is confirmed by 
EDX spectrum (Figure 3(b)). Au peak artifacts of sample 
preparation and support grid are noticed. In Figure 2(c), of the 
sample BTM10, the brightness domains are greater, the grain 
sizes are smaller and the brightness is stronger than that of 
Figure 2(b), since MgO content is greater than that of the 
samples BTM0 and BTM5. 

 

(a) 

 

(b) 

 

(c) 

 

Fig. 3.  EDX spectrum of MgO-BaTiO3 compared with pure BaTiO3. 
(a) BTM0, (b) BTM5, (c) BTM10 

We can see the effect of MgO on the microstructure of the 
sample. The doping with MgO led to a consequent decrease in 
the grain size. The samples sintered at 1250°C show that grain 
sizes are smaller, whereas, undoped BaTiO3 exhibits larger 

grain sizes (greater than 1µm). The most large grain size was 
estimated to be 10µm. For the sample BTM10, the grain size 
was in the order of 300nm. The result is in agreement with the 
findings in [21]. Incorporation of MgO particles in BaTiO3 led 
to the grain growth inhibition of the composite. Even in other 
system such as (Ba1-xCax)mTiO3–MgO–SiO2, MgO has been 
detected in the grain boundary region where MgO acts as a 
grain growth inhibitor [8, 26].  It is thus confirmed that in a 
MgO–BaTiO3 system the grain growth is inhibited by the 
secondary phase which can be due to excess of MgO, existing 
in the grain boundary. 

EDX mapping of elemental distribution of Ba, Ti, Mg and 
O has shown that MgO is highly dispersed in the BaTiO3 
matrix. We can see that the density of Mg in the BTM10 
sample is greater than that of the sample BTM5. The 
distribution of the chemical elements is homogenous except for 
Mg in BTM10 probably near the grain boundaries where the 
solid solutions can be located. The non-homogeneity is 
characterized by a strong concentration in these regions. These 
are the dark regions in the SEM image representing the 
morphology of the sample. The SEM image and mapping of 
elemental distribution shows that BaTiO3 seems to be covered 
with MgO particles. 

A. X-Ray Diffraction  

The diffraction pattern of X-ray (XRD) of these powders 
was performed for 45min at angle of 2θ, in temperatures 
ranging from 20°C to 80°C. The XRD spectra of the samples, 
BTM0, BTM5 and BTM10 sintered at 1250°C, are shown in 
Figure 4. The pure BaTiO3 spectrum has been used as a 
reference. 

 

(a) 
 
 
 
 
(b) 
 
 
 
 
(c) 

Fig. 4.  XRD spectra of (a) BTM10, (b) BTM5 and (c) BTM0 sintered at 
1250°C 

1) BTM0 

A representative XRD spectrum of the sample BTM0 is 
shown in Figure 4(c). The XRD study confirms the formation 
of the cubic system. All diffraction peaks coincide to that one 
of reference code 01-074-1964 where lattice parameter was 
equal to 4.0060Å. The obtained diffraction pattern is 
characteristic of a single perovskite phase. 



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2) BTM5 

The XRD spectrum of the sample BTM5 (Figure 4(b)), 
reveals that the microstructure consists of three phases: BaTiO3 
grain (primary phase) characterized by a peak appearing at an 
angle of 2θ=31.559° and corresponding to (110) reflection 
plane. The other phases, MgO and TiO2 are characterized by 
peaks appearing, at angles 2θ=42.917° and 2θ=28.527° and 
correspond to (200) and (421) refection planes respectively. 
The peak corresponding to the reflection plane is smaller (421). 
The parameters of these phases are given in the Table I. The 
increase in lattice constant of MgO-doped BaTiO3, supports 
that Mg2+ ions occupy Ti sites and expand the cell size, which 
is compatible with the acceptor doped behavior of MgO-doped 
BaTiO3. Three phases are detected in BTM5. The result 
suggests that the solubility limit of MgO in BaTiO3 has been 
exceeded whereas authors in [21] evaluate it between 1 and 1.5 
at.%. They found only a second phase (MgO) from 2 at.% of 
MgO. In [22] where MgO content was only 1.0 vol%, the 
secondary phase (MgO) has not been detected. However, our 
samples contain more than 5 mol% MgO. The solid solution 
between MgO and BTO occurred by dissolution of a low 
amount of MgO (<1.5 at.% MgO) into BaTiO3 and Mg

2+ 
replaces Ti4+, since the ionic radius of Mg2+ is larger than that 
of Ti4+. This result is in agreement with [8, 16, 21, 22]. As our 
samples contain more than 1.5 at.% MgO, other phases of MgO 
and TiO2 have been detected. MgO phase is the non-dissolved 
excess which is located in the grain boundaries. Furthermore, 
TiO2 phase was formed via the reaction of MgO with BaTiO3. 
The Ti atoms seem also segregated in the grain boundaries 
under oxide form. The segregation phenomenon is explained 
below using the energies of oxides formation. Otherwise, in the 
multi-component BaTiO3-based ceramics, the Ti-rich phase 
forms via the reaction of excess TiO2 with BaTiO3 but MgO 
addition suppresses the Ti-rich phase as reported in [20]. Our 
bi-component sample (BTM5) seems to be insufficient to 
suppress the Ti-rich phase. 

TABLE I.  PARAMETERS OF CHARACTERISTIC PHASES – BTM5 

Phase 
Reference 
code 

Crystal 
system 

a (Å): b (Å): c (Å): 
Density 
[g/cm3] 

BaTiO3 01-075-0461 Cubic 4.0119 4.0119 4.0119 6.00 
MgO 01-078-0430 Cubic 4.2112 4.2112 4.2112 3.56 
TiO2 01-088-1175 Tetragonal 4.5172 4.5172 2.9400 4.42 

 

3) BTM10 

The XRD spectrum of the sample BTM10 (Figure 4(a)) 
reveals that the microstructure consisted mainly of four phases: 
i) A primary phase (BaTiO3 grains) characterized by a peak 
appearing at an angle 2θ=31.559° and corresponds to (110) 
reflection plane, ii) the MgO phase characterized by a peak 
appearing at an angle 2θ=42.906° and corresponds to (200) 
reflection plane, iii) the TiO2 phase characterized by a peak 
appearing at an angle 2θ=27.911° and corresponding to (110) 
reflection plane, and finally iv) the TiO phase characterized by 
a peak appearing at an angle 2θ=43.671° and corresponding to 
(240) reflection plane. The detection of TiO phase indicates 
that 10 mol.%, as ratio of MgO, begins to reduce a part of TiO2 
phase into TiO phase. The parameters of these phases are given 
in Table II. We can see that MgO density has increased in 

comparison with the density of BTM5 (Table I), while those of 
BaTiO3 and TiO2 have kept the same values. The result is in 
agreement with [27], and indicates that the amount of 
intergranular pores is decreasing with increasing MgO. 
Consequently, the hardness of the BaTiO3-MgO composite 
increased with increase in the MgO content. 

TABLE II.  PARAMETERS OF CHARACTERISTIC PHASES – BTM10 

Phase 
Reference 
code 

Crystal 
system 

a (Å): b (Å): c (Å): 
Density 
[g/cm3] 

BaTiO3 01-075-0461 Cubic 4.0119 4.0119 4.0119 6.00 
MgO 01-078-0430 Cubic 4.2123 4.2123 4.2123 4.21 
TiO2 01-088-1175 Tetragonal 4.5170 4.5170 2.9400 4.42 
TiO 01-072-0020 Monoclinic 5.8550 9.3400 4.1420 4.91 

 

The models of diffusion and segregation, based on the 
sublimation enthalpies (bond energy) and the bond-breaking 
theory, are detailed in [28-30]. A preferential interaction 
coefficient (β) between the various atoms has been used to 
explain the evolution of the segregation. Concerning BaTiO3, 
β=	∆G����

� − G
��
� , G����,
��

�  are the enthalpies of mixing of 
the intermetallic compound. 

If β>0 there is interaction between Ba and oxygen. The 
segregation energy of Ba increases with the superficial 
concentration of O. 

If β<0, the interaction between Ba and oxygen is of 
repulsive type. The element with the stronger tendency to 
segregate will push the other elements towards the bulk. 

The obtained results concerning the sample BTM10 can be 
explained as follows.  

Taking account of mixing enthalpies of components BaO  
(-609.4kJ/mol), MgO (-603.6kJ/mol), TiO2 (-940kJ/mol), Mg

2+ 
(-4.66.85kJ/mol), Ti (468kJ/mol), the component having the 
lowest heat, of sublimation, segregates to grain boundaries (or 
to the surface) and the element that has the stronger tendency to 
segregate, pushes the other elements towards the bulk. The 
calculation method of segregation energy is developed in [28-
30] The TiO2 enthalpy is the smaller (β=-331). This one 
segregates to grain boundaries and pushes MgO to the bulk, 
therefore Mg2+ substitutes for Ti4+, since Ti4+and Mg2+ ions 
have respectively, 0.605 and 0.720Å radius. Mg2+ ion is more 
likely to replace the Ti4+ions instead of substituting for Ba2+ 
(1.61Å) [16]. Also, as the mixing enthalpies of components 
BaO and MgO are very close, the dissolution of MgO into 
BaTiO3 was easier. Thus, when MgO content is greater than 
1.5% (as carried out in [21]), the exceed is located in the grain 
boundaries or adsorbed at the surface [16, 23].   

Concerning the fourth phase (TiO), it is known that beyond 
the oxygen solubility limit into titanium, different oxides can 
be formed such as Ti6O, Ti3O and TiO. However, stability of 
TiO has been obtained for an oxygen content between 34.5 
at.% and 55.6 at.% [31]. The ratio of measured oxygen (60.25 
at.%) is beyond this limit confirming the stability of the TiO 
phase. However, the driving force for the formation of the TiOx 
originates from the respective energies of formation [32]. 
Segregation and Ti oxide formation depend on temperature, 
oxygen pressure and exposition time. TiO phase has been 



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detected only in BTM10 which contains 60.25 at.% oxygen. 
The energy of TiO formation is greater than that of TiO2, 
therefore, it is expected to detect, especially TiO2 but the result 
indicates reduction of TiO2 into TiO if one considers that the 
titanium segregates, under TiO2 form. In this case, the chemical 
reaction of TiO2 reduction can be considered. As the energy of 
TiO formation (-517.9kJ/mol) is greater than that of BaO, β 
will be greater than 0, since it is equal to 91.5 kJ/mol. Thus, 
TiO cannot segregate from grains towards grain boundaries. It 
is formed in the grain boundaries after the reduction of TiO2 
into TiO. The chemical reaction can be explained by using 
Ellingham diagram which shows the stability of the oxide as a 
function of temperature. A given metal can reduce the oxides 
of all metals whose lines lie	above its own on the diagram. For 
Mg, 2Mg � O� ↔ 2MgO line lies below the Ti � O� ↔	TiO�	 
line and so Mg can reduce TiO2 into Ti. For higher content of 
MgO (greater than 5 mol%.) a part of TiO2 is dissolved in the 
matrix, another part is reduced into TiO if the partial oxygen 
pressure in the matrix is lower than the equilibrium pressure 
value with the metal oxide at a given temperature. The 
remainder of TiO2 is located in the grain boundaries. The result 
is in agreement with [20-22] since MgO was detected in the 
grain boundary regions of the system.  

TiO2 reduction into TiO, can be explained in the following 
way. Ti atoms, or a portion of them, can segregate in the grain 
boundaries under metallic form, instead of oxide form, and Mg 
atoms (under metallic form) diffuse into the matrix. Oxidations 
of Ti and Mg occur respectively in the grain boundaries and in 
the matrix. The formed oxides will depend of the oxygen 
amount in the matrix. If the oxygen amount located in the 
grains boundaries is low, TiO oxide can be formed, in addition 
to TiO2 oxide. Finally, from the results of the microstructure, 
density data and XRD analysis as reported in [22] suggest that 
a quantity of MgO did not dissolve into the BaTiO3 and 
remains present under the form of phase inclusion in the 
BaTiO3 matrix and is located in the BaTiO3 grain boundaries. 
Some Mg2+ ions have dissolved  into the lattice to substitute 
Ti4+ ions on the B site of BaTiO3 maintaining the perovskite 
structure of solid solution with additional phases such as TiO2 
and TiO when MgO content is greater than 5 mol%. The results 
confirm the ones carried out in [21]. Concerning the 
microstructure of this system, abnormal grain growth was 
found in pure BaTiO3 with a 10µm average grain size. After 
addition of MgO particles into the system, the grain size 
decreased to less than 1µm for BTM5 and continuously 
decreased, with increasing MgO content (sample BTM10). 
MgO incorporation in the grain boundaries might be the grain 
growth inhibitor as reported in [8, 20-22]. 

High and stable electric permittivity, over a broad 
temperature range is significant for BaTiO3-based ceramics due 
to their use in multi-layer ceramic capacitors [20, 23]. MgO is 
an important additive in BaTiO3-based ceramics, because of its 
interesting electric properties. It has low electric permittivity (9 
to 10.1), high dielectric strength (10 to 35kV/mm), apparent 
porosity null (%), tgδ around 9.10-3 and high use temperature 
(1800°C) [33-35]. The presence of MgO in BaTiO3 matrix 
decreases the intergranular pores and increases the hardness of 
the MgO-BaTiO3 composite [27]. The four samples (BMT15, 

BMT20, BMT30 and BMT50), have been processed to achieve 
ultra-broad-temperature stability.  

B. Temperature Dependence of Dielectric Loss 

Energy losses in ferroelectric materials are one of the most 
critical issues of high power devices. Ferroelectrics combined 
with MgO as a function of intrinsic and extrinsic defects should 
have other behavior regarding dielectric loss. The tgδ of a 
dielectric material is a useful indicator of dielectric loss. The 
samples with uniform microstructure, narrow grain size 
distribution, and less defects, exhibits low dielectric loss 
properties. Figure 5 shows the tgδ of the BTM0, BTM5, 
BTM10 samples over a temperature ranging from 25 to 300°C. 

 

 
Fig. 5.  tgδ versus temperature of all samples 

BTM0 exhibits broad peak between 270°C and 290°C. The 
dielectric loss increases with increasing MgO content. The 
maximum values of tgδ for the three samples are ∼ 0.15, 0.25 
and 1.15 and correspond to temperatures 285°C, 270°C and 
270°C respectively. For BTM5 and BTM10 the maximum is 
shifted to 270°C. The moving of loss peaks towards low 
temperature with increasing Mg content has been reported in 
[19]. In higher temperature range (200-500°C), the high 
dielectric loss peak may be induced by the polarization of free 
space charge associated with a thermally active relaxation 
process. The results are in agreement with [19-21, 36]. Authors 
in [21] attribute the result to the increase in the oxygen 
vacancies. In our case the oxygen vacancy concentration 
increases with increasing MgO content, since Mg2+ is an 
acceptor for BaTiO3 and a double ionized oxygen vacancy 
(V0

++) is formed in addition to the reduction of TiO2 into TiO 
phase. However, MgO addition with multi-component BaTiO3-
based ceramics, for example BaTiO3 co-doped with Y, Ga and 
Si [8], reduces dielectric loss, because of Y3+doping. When the 
amount of MgO increases, (BTM15 and BTM20), the maxima 
of the loss curves shifted towards lower temperatures. These 
curves are characterized by oscillations around 200°C. At this 
temperature, the losses are greater than that of BTM5 and 
BTM10. The curve of the sample BTM20 presents a peak well 
resolved at 200°C. However, for the samples BTM30 and 
BTM50, the losses increase in comparison with that of BTM15 
and BTM20, to reach respectively maxima at 9 and 12. These 
peaks are shifted towards higher temperatures (300°C) in 
comparison with that of BTM15 and BTM20. The increase of 
the losses can be so attributed to the increase of the oxygen 



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vacancies with the increase of MgO such as previously 
explained for BTM5 and BTM10. 

C. Temperature Dependence of Electrical Resistance  

Figure 6 shows the resistance versus temperature, in the 
temperature range from 25°C to 400°C, of all samples. It is a 
typical resistance-temperature characteristic of a BaTiO3 based 
PTCR material. Impurities and lattice imperfections play an 
important role in the exhibition of the PTC effect, in the doped 
samples, since the losses are in connection with these 
imperfections [21]. Their conductivities are influenced by 
intrinsic defects such as oxygen vacancies and cation 
vacancies, and the extrinsic defects produced by dopant 
addition. Here, divalent Mg ions (under oxide form) are added 
to substitute Ti ions in the BaTiO3. The conductivity seems to 
be influenced by oxygen vacancies generated by Ti, and the 
lattice deformation of the composite (4.0119Å) is larger than 
that of pure BaTiO3 (4.0060) (see Tables II and III), proving 
that Mg substitutes Ti. TiO phase has been detected in BTM10, 
contributing to cation vacancy generation. The evolution of 
resistance versus temperature in Figure 6 shows the influence 
of these imperfections on the resistance. We can see that as the 
MgO content increases, the resistance is increasing along. 
However, the switching temperatures of the samples BTM0 
and BTM5 are around 270°C, whereas that of BTM10 is 
located at 225°. The characteristic of BTM10 presents 
oscillations below the switching temperature (225°C). Authors 
in [17] attribute the temperature stability of the resistance, 
below the switching temperature (of PTCR ceramics), to the 
uniform grain size. 

 

 
Fig. 6.  Resistance versus temperature of all samples  

Looking to the SEM image in Figure 2(a)-(b) 
corresponding to the samples BTM0 and BTM5, the grain sizes 
are lightly different, whereas the grain size, in the two samples, 
is in the order of µm. The switching temperature of the two 
samples is remains equal to 270°C. Only the amplitude of 
BTM5 is enhanced beyond 105Ω because of MgO doping. 
However the grain size of BTM10 (Figure 2(c)) is smaller than 
that of the two precedent samples, in the order of a few 
hundred nanometers. We can see also that the resistance of this 
sample evolves differently. This one presents a broad peak 
where its maximum (smaller than that of BTM5) begins at 
225°C and ends by oscillations until 350°C. The resistance, at 
room temperature, increases with MgO content increasing but, 
that of BTM10 decreases at 100°C, becomes smaller than that 
of BTM5, and afterwards increases again.  

However, the curves of the samples BTM15, BTM20 are 
close in point of view form, and evolve in the same way with 
the sample BTM10. The maxima are less broad than that of 
BTM10 and their maxima are shifted towards 175°C. The 
minima are higher than the ones of the BM10. The sample 
BTM30 has a broad maximum which begins at 175°C and ends 
at 270°C. Its minimum is higher than the ones of BTM15 and 
BTM20. However, the curve of the sample BTM50 begins by a 
minimum, around 10000, greater than that of all other samples, 
and afterwards it increases to reach a maximum (around 
30000), greater than that of all other samples. It is inferred that 
more MgO content reduces more TiO2 into TiO or even into Ti, 
more cation vacancies are generated and the resistance is rising. 
This maximum appears at the Curie temperature (125°C) and 
ends with oscillations with a minimum well resolved at 300°C. 
These results confirm that, as MgO content increases, the 
dielectric loss of MgO-doped BaTiO3 increases and Curie 
temperature shifts lower. Consequently, the resistance of the 
system increases. The result is in agreement with the findings 
in [21].  

D. Electric Permittivity 

Figure 7 shows the electric permittivity of MgO-doped 
BaTiO3, for various MgO contents, in a temperature range from 
20°C to 300°C. A sharp dielectric peak is recorded at Curie 
temperature (120°C) for BTM0. This TC value has been found 
equal to the one reported in [20] for multicomponent BaTiO3-
based ceramics without MgO. Electric permittivity of BTMO 
reaches almost 6000 while in [20], it is only 1700. However, 
MgO effect on BaTiO3 begins to appear on BTM5 by an 
enlargement of εr peak. εr maximum (5000) is located at 50°C. 
This enlargement of εr peak, has been indicated in [20]

 for 
samples containing 1.0wt%, 1.5wt% and 2wt% MgO, where 
maxima (around 2000) was located at 250°C. However, εr of 
BTM10 and BMT15, corresponding to the maximum and 
TC=80°C, has been evaluated to 4500 and 4250 respectively. 
The minima are located around 240°C. A broaden peak has 
been recorded for BTM5. Mg plays a role, in Curie peak 
depression [8]. The εr peak is shifted towards lower 
temperatures. Authors in [21] attribute this result to the 
diffuseness of the phase transition. The electric permittivity 
decreases with increasing MgO content. This is in agreement 
with [8, 16, 21-23]. Our samples contain MgO, TiO2 and TiO 
phases in the grain boundaries and even perhaps Ti in BTM30 
and BTM50. BTM30 and BTM50 can be even two phase 
materials, with MgO as continuous phase. The grain boundary 
is a non-ferroelectric phase, therefore its electric permittivity is 
lower. Otherwise, the permittivity at room temperature can be 
explained by the ionic polarization. This one can be calculated 
using the Clausisus-Mossotti equation [8]. εr decreases with 
increasing Mg, because of the decrease in ionic polarizability 
(α) of the dipole as shown in [8]. The more the MgO content is, 
the smaller is the grain size, and the lower the εr. This justifies 
that εr changes as a function of MgO content over the studied 
temperature range (from ambient temperature to 250°C). At 
250°C and beyond, the curves of εr (BTM0 and BTM10) 
present a minimum and increase again. However, for BTM5, 
the minimum appears at 350°C from which εr begins to 
increase slowly but remains smaller than that of BTM0 and 
BTM10. Concerning the samples BTM20 and BTM 30, the 



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curve evolution of εr kept the same form but their maxima, 
evaluated respectively to 4250 and less than 4000, are shifted 
towards 100°C. With 20 mol.% of MgO and more (30 mol.%.) 
as dopant, TC shifts slightly again towards higher temperatures. 
After the minimum located at 300°C, as we can see in Figure 7, 
the εr of BTM30 decreases in comparison with that of BTM20. 
This part of the curve is comparable with that of BTM10. The 
εr of BTM50 is equal to 500. It is 10 times smaller than that of 
BTM5 and 12 times smaller than that of BTM0. Its curve is 
characterized by small maxima at 120°C and 200°C and ends 
by an increase towards 1000 at 400°C. The εr of the sample 
BTM50 is close to the value found in [25] where BaTiO3 and 
MgO were both in the ratios 50% in volume. The εr, of the two 
phase material depends not only on the electric permittivity of 
the two phases (MgO and BTiO3), but it is highly affected by 
the structure (phase distribution and grain size) and the stress 
level between the phases as a result of the differences in their 
thermal expansion result [25]. The two phases, are promising 
for the development of high electric permittivity and high 
dielectric strength capacitors, therefore, the breakdown voltage 
is expected to be high, since the paraelectric (MgO) phase is 
continuous at this concentration [25]. Our results confirm the 
findings in [25] since TiO2 and TiO phases have vanished in 
BTM50. Sample BTM50 is a two phase material which is 
promising to have excellent thermal shock resistance, 
mechanical strength, and chemical resistance preperties. 

 

 
Fig. 7.  Temperature dependence of electric permittivity 

IV. CONCLUSION 

The effects of MgO additions on the microstructure and the 
dielectric properties of BaTiO3, have been studied. Oxides 
MgO and TiO2 have been detected in the sample BTM5. MgO, 
TiO2 and TiO were detected in the sample BTM10. MgO 
addition at 10 mol.%. and more, reduces the TiO2 phase into 
TiO phase and can be even reduced into Ti phase. The grain 
size strongly depends on the MgO content. The average grain 
size of pure BaTiO3 was near 10µm, whereas that of doped 
samples was about 1µm for BTM5 and some hundred 
nanometers for BTM10. The bimodal microstructure of fine 
and large matrix grains in BTM0 has been attributed to the 
temperature effect and to the presence of titanium oxide. εr 
decreases with increasing MgO content, while grain size and εr 
decrease. The electric permittivity of BTM50 was 12 times 
smaller than that of BTM0.The maximum peak was broader for 
increased MgO content. The TC, of BTM10 and BTM15 has 
been evaluated to 80°C, and to 100°C for BTM20 and BTM30. 

Beyond 15mol.% MgO, TC is shifted again towards higher 
temperatures. The Curie temperature of BTM50 was equal to 
that of BTM0 (120°C). The conductivity is influenced by 
intrinsic defects, oxygen vacancies, and cation vacancies. The 
extrinsic defects were produced by dopant addition. Divalent 
ions (Mg) substitute Ti ions. Consequently, the conductivity 
was influenced by oxygen vacancies generated by Ti and the 
lattice deformation of the composite. The dielectric loss 
increases strongly with increasing MgO content. The loss peak, 
shifts towards low temperatures with increasing MgO content, 
whereas it may be induced by the polarization of free space 
charge associated with a thermally active relaxation process. 
The highest loss (tgδ=12) has been measured on the BTM50, 
whereas that of BTM30 was equal to 9. The lowest loss has 
been measured on BTM0 (tgδ=0.2) and BTM5 (tgδ=0.3). TiO2 
and TiO phases have probably vanished in BTM30 and 
BTM50 samples. These samples, particularly BTM50, can be 
considered as two-phase materials, which is promising 
regarding shock resistance, mechanical strength and chemical 
resistance properties. 

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