Indian Journal of Engineering & Materials Sciences
Vol. 15, April 2008, pp. 176-180
Preparation and characterization of perovskite PMN [Pb(Mg1/3Nb2/3)O3]
Kamal Singha & Tanveer Quazib*
a
Sant Gadgebaba Amravati University, Amravati 417 006, India.
Department of physics, R T M Nagpur University, Nagpur 400 033, India
b
Received 9 November 2006; acceptec 28 Februsry 2008
Lead magnesium niobate (PMN) of different compositions are prepared by combustion method using Pb(NO3)2,
Mg(NO3)2, Nb2O5, and urea. Obtained material is sintered at 870°C/3 h and the density of sintered pellet measured by using
Archimedes principle. The formation of phase has been confirmed by X-ray powder diffraction (XRD) pattern at room
temperature and phase change by high temperatures XRD analysis. The dielectric constant (εr) and dissipation factor (tanδ)
are measured at frequencies 100 Hz, 1 kHz and 10 kHz in temperature range of 25–200°C using 4192A LF impedance
analyzer. The composition (110% excess urea) has shown higher dielectric constant (approx.7000 at room temperature).
Keywords: Combustion, Solid state, Dielectric constant, Relative permittivity
Lead magnesium niobate (PMN) is one of the most
intensively investigated compound in the lead-based
relaxor ferroelectric family. It is used1-6 in the
multilayer ceramic capacitors, electrostrictive
actuators, optoelectronics, sonar projectors, novel
transducers for medical applications. In the form of
thin films, it is used in microelectronics as memory
chips (FRAM, DRAM) and integrated capacitors
because of its excellent electrical properties7-10,
associated with a low thermal expansion and low cost.
Over the past three decades, considerable efforts
have been made in the fabrication of PMN and PMNbased electro ceramics. Various synthesis methods
have been proposed and used to prepare PMN powder
with the cubic perovskite structure. Avoiding the
pyrochlore phase, whose occurrence significantly
degrades the dielectric properties of PMN8, and PbO
volatilization is a general major difficulty in its
preparation.
The solid state reaction among constituent oxides
(PbO, MgO and Nb2O5) at elevated temperature
(ceramic route) saw a major breakthrough in 1982, by
Swartz and Shrout12, who devised the well known
columbite method for the fabrication of pyrocholorefree PMN. The method consists of two stages first the
prepartion of columbite (MgNb2O6) and then its
reaction with the appropriate amount of PbO. This
method is most commonly used, even today, for the
_________________
*For correspondence (E-mail: [email protected])
synthesis of the Pb(Mg1/3Nb2/3)O313, though timeconsuming.
Several wet-chemistry processing routes have been
engineered in order to prepare a single phase PMN
pervoskite14-18. The powder synthesis can usually be
achieved at low temperature. However, many solution
processes involve sophisticated techniques which are
complicated and lengthy processes, and in which they
often require a subsequent calcining step at elevated
temperatures, in order to achieve the desired
pyrochloro to perovskite conversion.
In recent years, combustion synthesis has been
established as a quick preparation process to produce
multicomponent oxide ceramic powders without the
intermediate decomposition and calcining steps19-24
and the said technique has already been tried in the
synthesis of PMN-based materials20.
There is high purity single phase perovskite
powder of composition PMN will not, by itself rise to
pyrochlore-free PMN ceramics, because of different
variation of initial composition of PMN at optimised
temperature. The objective of the work is to produce
single phase PMN ceramic which have maximum
density and relative permittivity, moreover, the
suppression of PbO loss during sinterinng is also
another major objective. Thus consideration is given
here to the phase formed, densification and dielectric
properties in PMN ceramic sintered at optimized
temperature of various composition for their
characterization.
SINGH & QUAZI: PREPARATION AND CHARACTERIZATION OF PEROVSKITE PMN [Pb (Mn)1/3 Nb2/3)O3]
Experimental Procedure
The chemicals used for the synthesis of PMN by
combustion method are Pb(NO3)2(>99%, Merck),
Mg(NO3)2(>99%, Merck), Nb2O5(99.5% SigmaAldrich)
used
as
cation
precursors
and
urea[CO(NH2)2] (>99%, Merck) as fuel. The
following three different composition of reactant have
taken.
1. PMN1: Pb(NO3)2: Mg(NO3)2 : Nb2O5 : Urea
(CO(NH2)2) :: 3 :1:1:6.67 (stiochiometric)
2. PMN2: Pb(NO3)2 : Mg(NO3)2 : Nb2O5 : Urea
(CO(NH2)2) :: 3:1:1:13.34 (100% excess urea)
3. PMN3: Pb(NO3)2 : Mg(NO3)2 : Nb2O5 : Urea
(CO(NH2)2) :: 3:1:1:14 (110% excess urea)
The reactants were first weighted and then mixed
in agate mortar and transferred to precleaned borosil
beaker. Then 50 mL distilled water was added to form
a homogeneous mixture by stirring with the glass rod
(cleaned by chromic acid) for 15 min. The reactants
were first melted in the beaker by heating upto 250300°C. The liquid froths for a while and then starts
thickening by giving out the gases evolved. Thus
prepared material is then transferred to muffle
preheated furnace at a 550°C, where oxidation occurs.
The reaction occurred for 1 min and produces a dry
yellowish-brown fumes and very fragile foam. The
temperature was slowly lowered to 200°C and was
kept for 2 h for complete oxidation, finally foam
crumbled into powder and crushed into powder by
using ball mill.
The obtained materials were sintered at 870°C /3 h.
The powder was characterized by X-ray diffraction
(XRD) using Cu-Kα1 radiation PANalytical X-ray
diffractometer, at 40 kV and 30 mA in the range 20°<
2θ >60° with step size of 0.02° 2θ and scanning speed
of 0.5° 2θ per minute.The obtained materials were
also characterized at temperatures 200, 400, 600, and
800°C for 8 h under vacuum pressure 10-3 torr on
same diffractometer to obtain XRD of materials.
177
cell parameter a= 4.0490Å. However, some additional
reflection, which correlate with a pyrochlore phase of
composition Pb1.83Nb1.71Mg0.29 O6.39 (JCPDS file 37–
71) are found on some XRD pattern. This phase has a
cubic structure with cell parameter a=10 Å in space
group Fd3m(no. 227).
The relative percentage of perovskite and
pyrochlore phase present in each sintered ceramic
may be calculated from the intensities of the major Xray reflection for the pervoskite and pyrochlore
phases. In this connection, the following
approximation proposed by Swartz and Shrout12 was
employed
Wt% perovskitephase=
I perov
I pervo + I pyro
× 100
... (1)
Here, Iperov and Ipyro refer to the intensities of the
(110) pervoskite and (222) pyrochlore peaks
respectively, these being the most intense reflections
in the XRD patterns of both phases. Consequently, in
order to estimate the concentrations of pyrochlore
phase present in the different sample. Eq.(1) has been
applied to the diffraction patterns obtained and
density by Archmides principle, as given in Table 1.
Result and Discussion
Analysis of phases formed
XRD pattern of the PMN ceramics formed at
specific temperature (870°C/ 3 h) for different
compositions are given in Fig. 1. The strongest
reflections in the majority of the XRD patterns
indicate formation of the pervoskite phase of PMN,
which was matched with JCPDS file 27–1199. To a
first approximation, this phase has a cubic pervoskitetype structure in space group Pm3m (no. 221), with
Fig. 1— XRD pattern of PMN1, PMN2 and PMN3, at room
temperature
INDIAN J ENG. MATER. SCI., APRIL 2008
178
The partical size is calculated by considering, the
coherrently diffracting domain size (dXRD) was
calculated from the full width at half maximum of
(110) diffraction peak using the Scherrer formula26,
which assume the small crystalline size to be the only
case of line brodening. [Eq. (2)].
Table 1—Effect of composition on phase formation and
densification
Composition
Density (%)
PMN1
PMN2
PMN3
Perovskite
(wt%)
90
96
90
Pyrochlore
(wt%)
10
4
10
Density
%
4.909
5.628
5.890
Table 2—Particle size of PMN1, PMN2, PMN3
Composition size(nm)
Crystaline size (nm)
PMN1
PMN2
PMN3
41
52
34
Fig. 2—High temperature XRD pattern of PMN1 at 200, 400, 600
and 800°C
dXRD =
kλ
β (θ ) cosθ
... (2)
Where λ is X-ray wavelength, β(θ) is FWHM of the
diffraction line, θ is the angle of diffraction and the
constant k~1 .The particle size of different
compositions of PMN is shown in Table 2
The high tempreture XRD of PMN1, PMN2 and
PMN3 as shown in Figs 2-4 respectively. There is
phase change observed between range of 200-800°C
Dielectric response of the ceramic
Figure 5 depicts the variation of relative
permittivity (εr) and dielectric loss (tanδ) with
temperature at three different frequency 100 Hz, 10
kHz and 100 kHz for sample PMN1, PMN2 and
PMN3. It is evident from these that PMN3 have
higher relative permittivity (appox. 7000) and less
dielectric loss (appox. 0.04) at room temperature than
Fig. 3—High temperature XRD pattern of PMN2 at 200, 400, 600
and 800°C
SINGH & QUAZI: PREPARATION AND CHARACTERIZATION OF PEROVSKITE PMN [Pb (Mn)1/3 Nb2/3)O3]
179
Fig. 5—Variation of relative permittivity dissipation factor for
PMN1, PMN2 and PMN3
References
Fig. 4—High temperature XRD pattern of PMN 3 at 200, 400,
600 and 800°C
PMN1 and PMN2. for PMN3 (110% excess urea) the
relative permittivity and dielectric loss less varing with
the frequency, with the increses frequency the
dielectric constant decreses and dielectric loss increses.
The relative permittivity of PMN3 is higher at room
temperature these is due to higher compactness have
small particle size and higher density
Conclusions
The XRD show that PMN 2 (100% excess urea)
have sharp peak and higher intensity, which have
higher 96% perovskite phase than PMN1 and PMN3,
but the dielectric constant of PMN 3 maximum
(~7000) and less dielectric loss as compared to PMN1
and PMN2 due to small particle size and higher
density and close packing. However, PMN3 (110%
excess urea) better for obtain maximum permittivity
(~7000) at room temperature.
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