X-ray diffraction, dielectric, conduction and Raman studies inNa0.925Bi0.075Nb0.925Mn0.075O3 ceramicChiheb Chaker, Y. Gagou, N. Abdelmoula, J.-L. Dellis, C. Masquelier et al. Citation: J. Appl. Phys. 111, 044101 (2012); doi: 10.1063/1.3684961 View online: http://dx.doi.org/10.1063/1.3684961 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v111/i4 Published by the American Institute of Physics. Related ArticlesGrowth and piezo-/ferroelectric properties of PIN-PMN-PT single crystals J. Appl. Phys. 111, 034105 (2012) Dielectric relaxation in the DyMn1−xFexO3 system J. Appl. Phys. 111, 034104 (2012) The effect of Li-substitution on the M-phases of AgNbO3 J. Appl. Phys. 111, 024107 (2012) Response to “Comment on ‘The electromagnetic property of chemically reduced graphene oxide and itsapplication as microwave absorbing material’” [Appl. Phys. Lett. 100, 046101 (2012)] Appl. Phys. Lett. 100, 046102 (2012) Evidence of ferroelectricity and phase transition in pressed diphenylalanine peptide nanotubes Appl. Phys. Lett. 100, 043702 (2012) Additional information on J. Appl. Phys.Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors

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X-ray diffraction, dielectric, conduction and Raman studiesin Na0.925Bi0.075Nb0.925Mn0.075O3 ceramic

Chiheb Chaker,1,2,a) Y. Gagou,2 N. Abdelmoula,1 J.-L. Dellis,2 C. Masquelier,3

H. Khemakhem,1 and M. El Marssi21Laboratoire des Materiaux Ferroelectriques (LMF), Unite de Recherche Physique-Mathematiques05UR15-04, Universite de Sfax, Faculte des Sciences de Sfax, Route de Soukra km 3,5 - B.P.1171,3000 Sfax, Tunisia2Laboratoire de Physique de la Matiere Condensee (LPMC), Universite de Picardie Jules Verne,Pole Scientifique, 33 rue Saint-Leu, 80039 Amiens Cedex 1, France3Laboratoire de Reactivite et Chimie des Solides (LRCS), UMR 6007, Universite de Picardie Jules Verne,Pole Scientifique, 33 rue Saint-Leu, 80039 Amiens Cedex 1, France

(Received 12 August 2011; accepted 9 January 2012; published online 17 February 2012)

Ceramic with composition Na0.925Bi0.075Nb0.925Mn0.075O3 (NNBM0075) was synthesized by high

temperature solid state reaction technique. It was studied using X-ray diffraction (XRD), dielectric

measurements and Raman spectroscopy. The sample crystallizes in orthorhombic perovskite

structure with space group Pbma at room temperature. Dielectric properties of the ceramic was

investigated in a broad range of temperatures (�150 to 450 �C) and frequencies (0.1–103 kHz), and

show two different anomalies connected to the symmetry change and electrical conductivity.

Dielectric frequency dispersion phenomena in the NNBM0075 ceramic was analyzed by

impedance spectroscopy in the temperature range from 55 to 425 �C. The Cole-Cole analysis based

on electrical circuit and least square method was used to characterize the conduction phenomenon.

A separation of the grain and grain boundary properties was achieved using an equivalent circuit

model. The different parameters of this circuit were determined using impedance studies. Four

conduction ranges, with different activation energies, were determined using the Arrhenius

model. Raman spectra were studied as a function of temperatures and confirmed the X-ray and

dielectric results. This composition is of interest for applications due to his physical properties and

environmentally friendly character. VC 2012 American Institute of Physics. [doi:10.1063/1.3684961]

I. INTRODUCTION

The past few years have seen a flurry of studies on ferro-

electric materials due to their large range of applications:

capacitors using their high dielectric permittivity, trans-

ducers and actuators using their piezoelectric properties and

ferroelectric memories using the remanent polarization of

these materials. Our study is based on the modification of

Na1-xBixNb1-xMnxO3 ceramics belonging to the system

NaNbO3-BiMnO3. These compounds show relaxation phe-

nomenon visible in the dielectric permittivity and conductiv-

ity dependences. It is worthwhile mentioning that they

correspond to the niobate NaNbO3 and manganite BiMnO3,

which attract attention as multiferroic materials. There is

much interest in multiferroic materials1,2 showing simultane-

ous ferroelectricity, ferromagnetism, and ferroelasticity

given their potential applications in magneto-electrics and

spintronics. The ferromagnetism of BiMnO3, along with

recent experimentally verified ferroelectric (FE) behavior,3

makes this compound potentially interesting for technologi-

cal applications.

BiMnO3 attracts much interest as a multiferroic mate-

rial,4,5 where anti-ferroelectricity and magnetism coexist.6

However, despite of a large number of works on BiMnO3,

there is still no consensus on its FE properties. There are a

growing number of publications recently emphasizing that

FE properties of BiMnO3 have not been well established.7

On the other hand, pure NaNbO3 is anti-ferroelectric (AF) at

room temperature, the FE phase can be rather easily induced

by a small amount of appropriate dopants (e.g., Li or K) or

by application of a moderate electric field and also by intrin-

sic defects like oxygen vacancy.8–10

A preliminary work has been reported on (Na1-xBix(Nb1-yMny)O3 ceramics by Lawniczak-Jablonska et al.,11

where they have studied the chemistry and the structure. In

this system, the manganese valence is Mn2þ and in order to

fulfill the charge neutrality condition, the varying amounts of

x and y of the two constituents have to form a stable solid so-

lution at steady proportion of xBi : yMn¼ 3:2 while xBi3þ

replaced (1�x)Naþ and yMn2þ replaced (1�y)Nb5þ. In addi-

tion, a series of works were carried out by Molak et al.12,14

where they have also studied (Na0.75Bi0.25)(Mn0.25Nb0.75)O3

(Ref. 12) and (Bi1/9Na2/3)(Mn1/3Nb2/3)O3 (Refs. 13 and 14)

electric properties in which the manganese valence is Mn2þ

or Mn4þ. The (Na1-xBix)(Nb1-yMny)O3,11 (Na0.75Bi0.25)

(Mn0.25Nb0.75) O3,12 and (Bi1/9Na2/3)(Mn1/3Nb2/3)O3 (Ref.

14) ceramics were prepared by dry sintering at ambient air

pressure, using a two-stage synthesis process. In the first

stage, (Na1-x)(MnyNb1-y)O3 precursor phase was produced

from Na2CO3, Nb2O5, and MnO powders prepared with stoi-

chiometric proportions. In the second stage, the crushed con-

stituent of the precursor phase was mixed with Bi2O3, but ina)Electronic mail: chakerchiheb@yahoo.fr. Fax:þ 216 74 274 437.

0021-8979/2012/111(4)/044101/8/$30.00 VC 2012 American Institute of Physics111, 044101-1

JOURNAL OF APPLIED PHYSICS 111, 044101 (2012)

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(Bi1/9Na2/3)(Mn1/3Nb2/3)O3 (Ref. 13) ceramics preparation,

the same preparation method was used with the MnO2 precur-

sor instead of MnO.

In the present paper, we have studied the

NNBM0075 ceramic derived from the NaNbO3 and

BiMnO3 mixture where Naþ and Nb5þ cations are substi-

tuted by Bi3þ and Mn3þ, respectively. Compared to the

last studies,11–14 our system was prepared by a traditional

solid state reaction using the Mn2O3 precursor where the

valence of the manganese is Mn3þ. We have reported, in

particular, the structure, dielectric properties, conduction

phenomenon, and Raman scattering of NNBM0075 ce-

ramic. This ceramic exhibits many interesting features,

such as diffuse phase transition. It is therefore, of great

interest to study the origin of these remarkable dielectric

properties in this material. The structure analysis versus

temperature was studied using X-ray diffraction (XRD).

The diffuse phase transition, observed by dielectric meas-

urements and confirmed by Raman spectroscopy charac-

terizations, is in agreement with XRD measurements. A

relationship between dielectric properties and conduction

phenomenon through the modified Cole-Cole analysis is

reported. Equivalent circuit model, impedance, and

Arrhenius studies are carried out.

II. EXPERIMENTAL PROCEDURE

NNBM0075 ceramic was prepared by a conventional

standard solid state reaction technique. Powders of Na2CO3,

Nb2O5, Bi2O3, and Mn2O3 of high purity 99.99% were taken

in stoichiometric ratio, weighed and mixed in an agate mor-

tar for 2 h. The 5% excess bismuth oxide was added to com-

pensate for the expected evaporation during sintering. The

appropriate mixture of powders was pressed into pellets and

calcined at 900 �C in air for 10 h. After calcination, powder

was mixed for 2 h and pressed into 8 mm diameter and about

1 mm in thickness. Finally, the pressed pellet was sintered in

oxygen atmosphere at 1130 �C for 3 h.

X-ray powder diffraction pattern of the sample was

recorded at several temperatures using a high-resolution

Brucker D8 diffractometer with filtered cobalt Ka1 and Ka2

radiations (kKa1¼ 1.788970 A and kKa2¼ 1.792850 A) in the

angular range of 10� � 2h � 90� with 20 s counting time for

each step of 0.02� in order to determine the structure of the

NNBM0075 ceramic. A profile matching of the XRD spectra

were made using the FullProf software.15 A good fitting was

obtained using a pseudo-Voigt (pV) profile function and the

background level was defined by an interpolation polynomial

function. Raman scattering data was collected in the fre-

quency range 50-1000 cm�1 using a Raman spectrometer

(J.Y. T64000).

The compactness value C defined as the ratio between

the experimental density dexp (determined from the weight

and geometrical dimensions of the cylindrical pellets) and

theoretical density dtheor (determined from XRD) and the rel-

ative diameter shrinkage of ceramic disks was systematically

determined as DU/U¼ (Uinit – Ufin)/Uinit where Uinit and Ufin

represent initial and final diameter. Their values were 95%

and 0.15, respectively.

III. RESULTS AND DISCUSSION

A. X-ray diffraction analysis

Powder XRD patterns profile analysis of NNBM0075

ceramic, at the temperature range between room temperature

(RT) and 500 �C, was performed to determine structural

phase transitions in this compound. The structural analysis

shows a pure perovskite phase and a good homogeneity.

Figure 1 shows the XRD pattern of NNBM0075 sample

taken at room temperature. Experimental conditions and rel-

evant data for refinements at room temperature are reported

in Table I. The background was fitted by a polynomial inter-

polation function from about 90 chosen points. The refine-

ment takes into account instrument zero point, unit cell

parameters, and the profile shape related to instrument

parameters (U,V,W) through the Caglioti function. The cal-

culations lead to a rapid convergence with a mean reliability

factor v2¼ 1.41 deduced from all calculated diagrams

through this temperature range. We have successfully per-

formed profile adjustment in high temperature region basing

on NaNbO3 high temperature tetragonal phase with space

group P4/mbm (N� 127). The structure was stabilized when

decreasing temperature until 320 �C. Lattice parameters were

found to be closed and can be considered as pseudo cubic.

On the other hand, the room temperature phase was success-

fully refined in the orthorhombic system with space group

Pbma (N� 57). This structural symmetry is conserved until

175 �C with good reliability factors. We deduce that this

compound presents the existence of an intermediate phase

which seems to be stabilized in the space group Ccmm (N�

63). Refinement in this space group leads to a rapid conver-

gence and consistent parameters.

Moreover, we do not observe any other different inter-

mediate phase as it was proved in pure NaNbO3 by Ahtee

et al.16 and the phase diagram is shifted to the left side at

about 270 �C when compared with the transition observed by

Ishida et al.17 This phase transition is tetragonal to the ortho-

rhombic type as confirmed in X-ray data by the splitting of

the line (400) or (222) in the high symmetry to the line (044)

FIG. 1. (Color online) XRD pattern of Na0.925Bi0.075Nb0.925Mn0.075O3 ce-

ramic at room temperature.

044101-2 Chaker et al. J. Appl. Phys. 111, 044101 (2012)

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and (440) or (440) and, (404) in the low symmetry phases as

shown in Fig. 2. We can conclude that chemical elements

substitution in NaNbO3 lead to the destruction of two others

intermediate complementary phases; only one intermediate

antiferroelectric remained. Lattice parameters versus temper-

ature were shown in Fig. 3. Notice that for T< 300 �C, all

lattice parameters correspond to their real value (ao, bo, co)

in the orthorhombic structure accepted in the space groups

Pbma and Ccmm, respectively.

The lattice parameters ao¼ 2ap and bo¼ 2bp represent

the double value of the perovskite lattice ap and bp while

co¼ 2cp represents the double value of c-axis parameter of

the perovskite. This means that the unit cell in the ortho-

rhombic phases of the NNBM0075 ceramic represents then

eight times the perovskite unit cell. On the other hand, the

perovskite unit cell is doubled since ap and bp are multiplied

by square 2 in the quadratic phase of the NNBM0075 com-

pound at high temperature. To show coherent evolution of

the lattice parameter in the complete temperature range, the

lattice parameters are normalized as

aq ¼ 2 � ap=:ffiffiffi2p

and bq ¼ 2 � bp

� ffiffiffi2p

;

where aq and bq are the perovskite unit cell diagonal and

cq¼ cp for data with T> 300 �C where we can observe

clearly a tetragonal reorganisation of the structure. This con-

figuration, with 2ap� 2ap, leads to a rapid convergence of

the profile adjustment without any superstructure reflexion.

However, the reliability factors are better in the first case.

Notice that the stability of the NNBM0075 compound

having perovskite-type structure can be discussed in term of

the tolerance factor value defined by Goldschmidt,18 as

t ¼ 0:925 rNaþ þ 0:075 rBi3þð Þ þ rO2�ffiffiffi2p

0:925 rNb5þ þ 0:075 rMn3þð Þ þ rO2�½ �:

The distorted perovskite-type structure is stable over the

range 0.75 � t< 1. Based on Shannon’s ionic radii,19

r(Naþ)¼ 1.18 A and r(Bi3þ)¼ 1.20 A in an eightfold coordi-

nation, r(Nb5þ)¼ 0.64 A, r(Mn3þ)¼ 0.645 A in high spin

case and r(O2-)¼ 1.40 A in a sixfold coordination, the calcu-

lated tolerance factor of the NNBM0075 ceramic is

t¼ 0.893. This value was included in the distorted perovskite

stability range.

TABLE I. Experimental conditions and relevant data for refinements of the

NNBM0075 ceramic at room temperature.

Formula Na0.925Bi0.075Nb0.925Mn0.075O3

Crystal system Orthorhombic

Space group Pbma (N� 57)

a (A) 7.8135(3) (2ap)

b (A) 7.8001(4) (2bp)

c (A) 7.8316(11) (2cp)

Volume (A3) 477.305

Angles a¼b¼ c¼ 90�

Radiation type, source X-ray, Co

Wavelengths values used 1.78897 A and 1.79285 A

2h range, time/step 10-90, 20 s=0.02

Reliability factors Rp¼ 7.38, Rwp¼ 10.9,

Rexp¼ 9.14, v2¼ 1.41

FIG. 2. (Color online) X-ray diagram for several temperatures showing the

splitting of the line (400) or (222). Arrows show the frontier of the two phase

transitions.

FIG. 3. (Color online) Evolution of the lattice parameters of

Na0.925Bi0.075Nb0.925Mn0.075O3 ceramic as a function of the temperature,

showing standard deviations. The inset shows the volume of cell parameters

as a function of temperature.

044101-3 Chaker et al. J. Appl. Phys. 111, 044101 (2012)

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B. Dielectric measurements

Dielectric measurements were performed on pellets

ceramic which both sides are polished by platinised electrodes

using a cathodic sputtering technique with Baltec-SCD500.

The dielectric permittivity was measured as a function of

temperature at different frequencies. Measurements were

performed with a heating rate of 1 �C/min, using a Solartron

SI-1260 spectrometer in the temperature and frequency

ranges between �150 �C and 450 �C and 100 Hz to 103 kHz,

respectively. The temperature is controlled using a Linkam

TMS94 allowing a temperature stability of 60.1 �C.

Figures 4(a) and 4(b) show the temperature dependence

of the permittivities e0r and e00r determined for the NNBM0075

ceramic. On the e0r(T) curved presented in Fig. 4(a) and

according to the XRD analysis, two interesting behaviors

were noticed: a first anomaly at the temperature T1¼ 155 �Ccorresponding to the transition from the first anti-

ferroelectric (AF1) phase to the second anti-ferroelectric

(AF2) phase, and a second anomaly at the temperature

T2¼ 380 �C corresponding to the transition from the AF2

phase to the paraelectric (PE) phase. This intermediate AF2

phase seems to be stabilized at low frequencies and disap-

pears at high frequencies electrical field excitation as showed

clearly in Fig. 4(a), where the second anomaly vanishes for

high frequencies.

When analyzing the permittivity thermal hysteresis,

shown in Fig. 4(c) at the frequency 10 kHz, we remark 10 �Cunder room temperature where the heating and cooling

curves became again identical after a thermal hysteresis loop

of about 5 �C. That could be the Q phase considered as the

beginning (under �10 �C) of the FE as reported by Yuzyuk

et al.20 This temperature can be also considered as depolar-

ized temperature as reported by Ying et al.21 In addition,

this study shows that the value of the first temperature

(T1¼ 155 �C) is not depending on frequency, implying that

this composition is without any relaxor-type perovskite. A

similar behavior was seen in the Na1-xLixNbO3 (Ref. 22)

solid solution where the AF phase was observed up to

x¼ 0.02 and the ferroelectric Q-phase was appeared when

x> 0.03 as reported by Yuzyuk et al.23 and also in the

Na1-xLixNb1-xSbxO3 (Ref. 24) and Na1-xLixNbO3 (Ref. 25)

systems with compositions 0.05 � x � 0.15. The broadened

peaks indicate that the transition, in this composition, is of

diffuse type showing an important characteristic of a disor-

dered perovskite structure. It appears from experiments that

the titled compound has specific properties. In particular, a

clear evidence of enhanced dielectric anomaly around the

temperature 155 �C at heating and 150 �C at cooling runs

exhibiting then the existence of a thermal hysteresis of about

5 �C. That proves also a first-order-type structural transition

as shown in Fig. 4(c) at the frequency 10 kHz. The principal

parameters, determining the phase transitions and related to

the physical properties of the crystalline materials possessing

the oxygen octahedral, is a non-stoichiometric cationic sub-

stitution which may cause additional increase of an harmonic

electron-phonon interactions responsible for the phase transi-

tions, as it was shown for niobate.26 The loss factor

(tan d ¼ e00=e0), at different frequencies (100 Hz, 1 kHz, and

10 kHz), exhibits also a peak at the transition temperature TC

as shown in Fig. 4(d) where a dielectric loss of about

8� 10�2 was observed. The rapid increasing of loss factor in

the PE phase is related to the ionic conduction phenomena.

FIG. 4. (Color online) (a) Temperature de-

pendence of the permittivity e0r at various

frequencies of the NNBM0075 ceramic. (b)

Temperature dependence of the imaginary

part of the relative permittivity e00r at various

frequencies of the NNBM0075 ceramic. (c)

Temperature dependence of the dielectric

constant at 10 kHz (heating and cooling

runs) of the NNBM0075 ceramic. (d) Tem-

perature dependence of the dielectric loss

(tan d) of the NNBM0075 ceramic.

044101-4 Chaker et al. J. Appl. Phys. 111, 044101 (2012)

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C. Conduction phenomenon

1. Cole-Cole plot analysis

NNBM0075 ceramic presents also the presence of con-

ducting phenomenon. As we can see in Figs. 4(b) and 4(d),

the imaginary part of the dielectric permittivity and the loss

factor present a sharp increasing which suggests the presence

of conductivity. On the real part of dielectric permittivity, a

first anomaly at the temperature T1¼ 155 �C has been seen

and also a second anomaly around T2¼ 380 �C can be

observed for low frequencies (for example at 100 Hz). The

second anomaly must correspond to the change of a struc-

tural phase accompanied with ion motions through the com-

pound since the peak tends to vanish at high frequencies. So,

we perform our investigation using modified Cole-Cole anal-

ysis through our own simulation based on electrical circuit

model and least square method in order to optimize the e00-e0,Z00-Z0 or M00-M0 curve plots of the compound, where e00-e0,Z00-Z0, and M00-M0 are, respectively, the imaginary and real

part of the permittivity, the impedance and the electric mod-

ulus characteristic of the compound. The real (e0, Z0, M0) and

imaginary (e00, Z00, M00) parts of the complex parameters are

in turn related to one another as follows:

e� ¼ e0 � je00 where

e0 ¼ � Z00

xC0 Z02 þ Z002ð Þe00 ¼ � Z0

xC0 Z02 þ Z002ð Þ

8>><>>:

Z� ¼ Z0 � jZ00 ¼ 1

jxC0e�where

Z0 ¼ e00

xC0 e02 þ e002ð ÞZ00 ¼ e0

xC0 e02 þ e002ð Þ

8>><>>:

M� ¼ M0 þ jM00 ¼ 1

e�¼ jxC0Z� where

M0 ¼ e0

e02 þ e002

M00 ¼ e00

e02 þ e002;

8>><>>:

where x is the angular frequency linked to the frequency fby the relation x¼ 2pf, j2 ¼ �1 and C0 is the geometrical

capacitance. These relations offer wide scope for a graphical

analysis of the various parameters under different conditions

of temperature or frequency. The useful separation of inter-

granular phenomena depends ultimately on the choice of an

appropriate equivalent circuit to represent the sample

properties.

The displaying method data is in the complex plane in

which Z00 is plotted against Z0. In the ideal case, a plot of Z00

versus Z0 is a semicircle whose center lies in the Z0 axis and

whose intercepts with the Z0 axis. Figure 5 shows the com-

plex impedance plot of the NNBM0075 ceramic, plotting the

imaginary part Z00 against the real part Z0 at different tempera-

tures. Arrhenius type law was used to elucidate the conduc-

tion phenomenon and the activation energy calculation.

2. Equivalent circuit model

A better understanding of the conductivity mechanisms

requires an equivalent circuit model that provides the best

representation of the electrical properties. The overall elec-

trical properties of a polycrystalline ceramic have a contribu-

tion from grains and grains boundaries. In our case, the best

calculation is obtained using circuits containing resistor (R)

and a constant phase elements (CPE) instead of simple

capacitances. The best equivalent circuit modeling conduc-

tion phenomenon in this compound is constituted by a paral-

lel connection of one resistance R and two different CPE as

shown in Fig. 6. In this model, the resistance impedance is

ZR¼R and the CPE impedance is expressed as the Warburg

element by the formula,

ZCPE ¼1

A jxð Þa ;

where A is a physical quantity and a is the circuit parameter

which gives to ZCPE its limiting behavior as a capacitance

for a¼ 1, a resistor for a¼ 0, and an inductance for

a¼�1.27,28 Intermediate values correspond to Warburg im-

pedance.29 The Z00-Z0 curve fitting leads to the determination

of five parameters: the resistance R and two other parameters

(A and a) of each CPE. The resistance and the first CPE cor-

respond to the ceramic grain behavior and the second CPE

corresponds to interstice or grain boundary and space charge

behaviors modeled by CPE.

FIG. 5. (Color online) Complex-plane impedance plots for

Na0.925Bi0.075Nb0.925Mn0.075O3 at different temperatures.

FIG. 6. Equivalent circuit model for Na0.925Bi0.075Nb0.925Mn0.075O3

ceramic.

044101-5 Chaker et al. J. Appl. Phys. 111, 044101 (2012)

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3. Arrhenius study

In order to understand the conduction phenomena, we

have used the Arrhenius modeling equation,

r ¼ r0 e� DE=kTð Þ;

where DE is the activation energy, r0 is the pre-exponential

factor, k is the Boltzmann constant, and T is the temperature.

We have determined the conductivity of the sample bulk

response using the calculated resistors. The plot of logarithm

(r) as a function 1000/T of the NNBM0075 ceramic, shown

in Fig. 7, allowed us to highlight four areas characterized by

four different activation energies. The results are summar-

ized in the Table II.

When compared to dielectric measurements, we can

attribute the slope change occurring at the temperature of

275 �C to the beginning of the second anomaly observed in

er(T) variation at low frequencies. This can be attributed to

ions motion through the compound. Thermal energy is suffi-

cient to activate ions or carrier motion. The second slope

change corresponds to the paraelectric to anti-ferroelectric

structural phase transition at 155 �C. Every phase is charac-

terized by a different cohesion energy needed to structure

stability. The last slope change at 135 �C, corresponds to the

beginning of the diffuse phase transition. At this temperature

in the case of low frequencies, the system begins the struc-

tural change mechanism. These behaviors are in favor of ion

conduction that can be attributed to the displacement of

atoms at octahedral sites of the solution solid because of the

occupation disorder. In addition, the displacement can result

in jumping from one site to another because of the crystal

lattice dilatation.

D. Raman scattering

Raman spectroscopy measurements were performed

using the 514.5 nm calibration line from an argon ion laser

and analyzed using a Jobin Yvon T64000 spectrometer

equipped with a charge coupled device. An optical micro-

scope was used to focus the incident light as a spot of about

2 lm in diameter on the sample. Depolarized Raman spectra

were obtained in backscattering geometry.

Raman spectroscopy has been successfully used as a

tool for studying the structure and the phase transitions of

NaNbO3 (Refs. 30 and 31) and Li doped NaNbO3 (Ref. 22)

compounds. Figure 8 shows the temperature dependence of

the Raman spectra of NNBM0075 ceramics showing distinct

changes. As can be shown in Table III, the Raman peaks

reported in anti-ferroelectric phase of NaNbO3 (Ref. 32) at

95, 126, 157, and 186 cm�1 are forbidden in NNBM0075

ceramic. Similar room temperature spectrum of NNBM0075

is observed in the orthorhombic anti-ferroelectric phase of

Na1-xLixNbO3.22 This confirms the anti-ferroelectric charac-

ter of the NNBM0075 room temperature.

On the other hand, the temperature dependence of the

Raman spectra (Fig. 8) does not show any significant change

on heating up to the transition temperature TC. Above TC, the

symmetry changes obtained in X-ray refinements between

space groups Pbma and Ccmm have not been observed

significantly on Raman spectra, because of the broadened

Raman modes. We have observed the merging of Raman

modes around 800 cm�1 when the temperature approaches

300 �C. It is clear therefore that orthorhombic anti-

ferroelectric to paraelectric phase changes, in this wide tem-

perature range appear, when going to the paraelectric phase.

Above 160 �C, the intensity of all Raman modes decreases

gradually and disappears around 300 �C. This result confirms

the structural phase transition occurring at TC, observed by

XRD and dielectric measurements. In addition, our Raman

results confirm that the anti-ferroelectric paraelectric phase

transition is diffuse as suggested by the broad peak of the

dielectric maximum observed around TC.

FIG. 7. (Color online) Logarithm of r as a function 1000=T for

Na0.925Bi0.075Nb0.925Mn0.075O3 ceramic.

TABLE II. The values of the conductivity r0 and the activation energy DE

obtained at fitting with the modified Cole-Cole of the NNBM0075 ceramic.

Zone 1 from

T¼ 425 �C to

T¼ 275 �C

Zone 2 from

T¼ 275 �C to

T¼ 155 �C

Zone 3 from

T¼ 155 �C to

T¼ 135 �C

Zone 4 from

T¼ 135 �C to

T¼ 55 �C

r0 (Sm�1) 0.1075 1.2523� 10�3 3.0698� 10�10 1.1211� 10�6

DE (eV) 0.235 0.118 0.598 0.075

FIG. 8. (Color online) Raman spectra for Na0.925Bi0.075Nb0.925Mn0.075O3

ceramic at different temperatures.

044101-6 Chaker et al. J. Appl. Phys. 111, 044101 (2012)

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Based on the model purposed by Ross33 and the study

by Last34 and Quittet et al.,35 the vibrational modes of the

NNBM0075 ceramic derived from NaNbO3-BiMnO3 for the

composition x¼ 0.075 can be classified as internal modes of

the NbO6 octahedron and the lattice transitions involving

motion of the cations. The vibrational modes of an isolated

NbO6 octahedron can be decomposed into two pure bond

stretching vibrations of symmetry A1g(�1) and Eg(�2), two

interbond angle bending vibrations �5 and �6 of symmetry

F2g and F2u, respectively, and two vibrations �3 and �4, con-

sidered as combinations of stretching and bending, both of

F1u symmetry. The high frequency vibrational modes

observed at 605 and 560 cm�1 on NaNbO3 (Ref. 32) Raman

spectra are assigned as the �1 and �2 stretching mode in

NbO6, respectively. The observed mode wave numbers and

proposed assignments of NaNbO3 (Ref. 32) and NNBM0075

are collected in Table III.

For T> TC (Fig. 8), the normal modes are not Raman

active in the paraelectric phase, and the origin of their activa-

tion should be found in a strong disorder in the material lat-

tice. As shown in Fig. 8, the peak at 62 cm�1 of NNBM0075

at the temperature of 30 �C gradually decrease in intensity

and finally disappear as the temperature is increased. This

peak can be assigned as the translation modes involving Naþ

cation motion against the NbO6 octahedron. In addition, the

peaks at 820 and 870 cm�1 of NNBM0075 gradually

decrease in intensity as the temperature is increased, and this

evolution can be assigned as the structural transition from

orthorhombic to the cubic system at high temperature.

In fact, the peak attributed to the Nb-O phonon Raman

spectrum observed at 258 cm�1 for NaNbO3 but in the

NNBM0075 is observed at 250 cm�1 and 600 cm�1. The

peaks attributed to the Mn-O phonon were observed at 820

cm�1 and 870 cm�1. When the temperature increases all the

bands show significant broadening, a weaker intensity, and

shifted to the high frequency. This would be undoubtedly con-

nected with the disorder created on the A and B sites of

NaNbO3 as a consequence of Na/Bi and Nb/Mn substitutions.

The A1 transverse optical (TO) modes are observed as

broad lines at 260 cm�1 and 600 cm�1. The A1 longitudinal

optic (LO) modes can be identified at 820 cm�1 and 870

cm�1. Indeed, the Nb ions do not occupy the octahedral cen-

ters but eight positions slightly shifted on the cube diagonal.

The real instantaneous symmetry is lower than cubic and

which relaxes the selection rules. This behavior and width of

the Raman spectra mean that the substitution of NaNbO3 in

the A and B sites of the perovskite structure introduces an

important disorder in the structure.

IV. CONCLUSION

Well-sintered Na0.925Bi0.075Nb0.925Mn0.075O3 (NNBM0075)

ceramic was elaborated by solid state reaction method and

investigated by several physical experiments. The results are

summarized as follows:

(1) Lattice parameters are deduced from the whole pattern

profile refinement of the X-ray data. It was shown by

XRD at room temperature that the NNBM0075 com-

pound structure is of perovskite-type and crystallizes in

orthorhombic symmetry with space group Pbma.

(2) Dielectric measurements show one peak at TC¼ 155 �Cwithout any relaxor-type phenomenon, and also a second

anomaly at T2¼ 380 �C connected to symmetry change

and electrical conductivity.

(3) In order to understand the presence of electrical conduc-

tion in the NNBM0075 ceramic, we have used a modi-

fied Cole-Cole analysis based on electrical circuit and

the least square method in order to highlight the effects

of the charge carriers based on the Arrhenius-type

model. We have demonstrated that there is a conduction

mechanism piloted by four activation energies.

(4) The evolution of the Raman spectra at various tempera-

tures confirms our structural study and dielectrics results.

(5) We can consider that this compound is of a great interest

for technical applications as environmentally friendly

dielectric materials.

ACKNOWLEDGMENTS

We wish to thank Mr. Jean-Claude PICOT for his tech-

nical help and Mr. Karim DJELLAB for a scanning electron

microscopy (SEM) of the sample. Chiheb Chaker would like

to acknowledge the Cooperation French Institute (IFC) in

Tunisia for the financial support through the French level

higher scholarship (SSHN).

1M. Maglione and M. Belkaoumi, Phys. Rev. B 45, 2029 (1992).2W. Kleemann and J. Kreisel, Phase Transitions 79, 12 (2006).3A. Moreira dos Santos, S. Parashar, A. R. Raju, Y. S. Zhao, A. K.

Cheetham, and C. N. R. Rao, Solid State Commun. 122, 49 (2002).4T. Atou, H. Chiba, K. Ohoyama, Y. Yamaguchi, and Y. Syono, J. Solid

State Chem. 145, 639 (1999).5C. H. Yang, J. Koo, C. Song, T. Y. Koo, K. B. Lee, and Y. H. Jeong, Phys.

Rev. B 73, 224112 (2006).

TABLE III. Observed wave numbers of Na0.925Bi0.075Nb0.925Mn0.075O3

ceramic.

NaNbO3a � (cm�1) (300 K)

Na0.925Bi0.075Nb0.925Mn0.075O3

� (cm�1)

64 Naþ 60 Naþ

76 Naþ 71 Naþ

95

126

146 140

157

180 �6 179 �6

186

223 220

258 �5 250 �5

279

281

375 �4 371 �4

433 428

560 �2 544 �2

605 �1 600 �1

820

870

aReference 32.

044101-7 Chaker et al. J. Appl. Phys. 111, 044101 (2012)

Downloaded 17 Feb 2012 to 194.57.107.121. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions

6N. A. Hill, J. Phys. Chem. B 104, 6694 (2000).7W. Eerenstein, F. D. Morrison, F. Sher, J. L. Prieto, J. P. Attfield, J. F.

Scott, and N. D. Mathur, Philos. Mag. Lett. 87, 249 (2007).8Z. Kutnjak, C. Filipic, R. Pirc, A. Levstik, R. Farhi, and M. El Marssi,

Phys. Rev. B 59, 294 (1999).9F. Le Marrec, R. Farhi, M. El Marssi, J.-L. Dellis, M. G. Karkut, and D.

Ariosa, Phys. Rev. B 61, 6447 (2000).10I. P. Raevski, S. A. Prosandeev, A. S. Emelyanov, S. I. Raevskaya, E. V.

Colla, D. Viehland, W. Kleemann, S. B. Vakhrushev, J.-L. Dellis, M. El

Marssi, and L. Jastrabik, Phys. Rev. B 72, 184104 (2005).11K. Lawniczak-Jablonska, I. N. Demchenko, E. Piskorska, A. Molak,

J. Kachiarz, and M. Heinonen, Microchim. Acta 145, 95 (2004).12A. Molak, M. Paluch, S. Pawlus, J. Klimontko, Z. Ujma, and I. Gruszka,

J. Phys. D: Appl. Phys. 38, 1450 (2005).13A. Molak, M. Paluch, S. Pawlus, Z. Ujma, M. Pawelczyk, and I. Gruszka,

Phase Transitions 79, 447 (2006).14A. Molak and M. Pawelczyk, Ferroelectrics 367, 179 (2008).15J. Rodriguez-Carvajal, computer program FullProf, Laboratoire Leon

Brillouin, CEA-CNRS, version April 2008, LLB-LCSIM, 2008.16M. Ahtee, A. M. Glazer, and H. D. Megaw, Phil. Mag. 26, 995 (1972).17K. Ishida and G. Honjo, J. Phys. Soc. Jpn. 34, 1279 (1973).18P. Ganguly and C. N. R. Rao, J. Solid State Chem. 53, 193 (1984).19R. D. Shannon and C. T. Prewitt, Acta Crystallogr., Sect. A: Cryst. Phys.,

Diffr., Theor. Gen. Crystallogr. A32, 751 (1976).20Yu. I. Yuzyuk, R. A. Shakhovoy, S. I. Raevskaya, I. P. Raevski, M. El

Marssi, M. G. Karkut, and P. Simon, Appl. Phys. Lett. 96, 222904

(2010).

21Y. Ying, Z. Shuren, Z. Xiaohua and L. Jingsong, J. Mater. Sci. 41, 565

(2006).22W. L. Zhong, P. L. Zhang, H. S. Zhao, Z. H. Yang, Y. Y. Song, and H. C.

Chen, Phys. Rev. B 46, 10583 (1992).23Yu. I. Yuzyuk, E. Gagarina, P. Simon, L. A. Reznitchenko, L. Hennet, and

D. Thiaudiere, Phys. Rev. B 69, 144105 (2004).24C. Chaker, W. Elgharbi, N. Abdelmoula, H. Khemakhem, A. Simon, and

M. Maglione, J. Alloy. Compd. 481, 305 (2009).25C. Chaker, W. Elgharbi, N. Abdelmoula, A. Simon, H. Khemakhem, and

M. Maglione, J. Phys. Chem. Solids 72, 1140 (2011).26I. V. Kityk, M. Makowska-Janusik, M. D. Fontana, M. Aillerie, and F.

Abdi, J. Appl. Phys. 90, 5542 (2001).27P. Zoltowski, J. Electroanal. Chem. 443, 149 (1998).28J. Ross Macdonald, Impedance Spectroscopy: Emphasizing Solid Materi-

als and Analysis (Wiley & Sons, New York, 1987), p. 133.29J.-B. Jorcin, M. E. Orazem, N. Pebere, and B. Tribollet, Electrochim. Acta

51, 1473 (2006).30Y. D. Juang, M. L. Hu, and W. S. Tse, J. Appl. Phys. 76, 3746 (1994).31Yu. I. Yuzyuk, P. Simon, E. Gagarina, L. Hennet, D. Thiaudiere, V. I.

Torgashev, S. I. Raevskaya, I. P. Raevskii, L. A. Reznitchenko, and J. L.

Sauvajol, J. Phys. Condens. Matter 17, 4977 (2005).32Y. D. Juang, S. B. Dai, Y. C. Wang, W. Y. Chou, J. S. Hwang, M. L. Hu,

and W. S. Tse, Solid State Commun. 111, 723 (1999).33S. D. Ross, J. Phys. C 3, 1785 (1970).34J. T. Last, Phys. Rev. 105, A1740 (1957).35A. M. Quittet, M. I. Bell, M. Krauzman, and P. M. Raccah, Phys. Rev. B

14, 5068 (1976).

044101-8 Chaker et al. J. Appl. Phys. 111, 044101 (2012)

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