J. Modern Physics, 2010, 1, 93-99
doi:10.4236/jmp.2010.12014 Published Online June 2010 (http://www.SciRP.org/journal/jmp)
Copyright © 2010 SciRes. JMP
Structural, Magnetic and Dielectric Studies on
Strontium Substituted Nd2CuO4 System
Venugopalan Anbarasu, Appasamy Manigandan, Kandasamy Sivakumar*
Department of Physics, Anna University Chennai, Chennai, India.
Email: ksivakumar@annauniv.edu
Received March 7th, 2010; revised April 23rd, 2010; accepted May 15th, 2010.
The substitution of Strontium on T'–structured Nd2CuO4 system has been carried out through solid state reaction tech-
nique. From the Powder XRD patterns, it is found that the compounds are formed in single phase and crystallizes in
orthorhombic structure. The variation in lattice parameters with decreasing nature of volume of the prepared com-
pounds confirms the incorporation of lower atomic radii Strontium in Neodymium site. Surface morphology and ele-
mental composition studies are also carried out to know the nature of the compounds and effect of Strontium substitu-
tion in Nd2CuO4 system. The paramagnetic nature of all the prepared compounds has been identified through magneti-
zation studies and the results are correlated with the electron spin resonance studies by the way of variation in reso-
nance field and broad peak width. Increasing order of dielectric constant on higher doping concentration of Strontium
and the least value of dielectric loss at higher frequencies confirms the improved surface transport properties of the
prepared compounds.
Keywords: Ln2CuO4, Structural Analysis, Powder XRD, Dielectric Studies, Magnetization, ESR Analysis
1. Introduction
The Ln2Cu O4 oxides exhibit two different crystal struc-
tures with respect to the size of the Ln3+ ion (Ln, Lan-
thanide element) that differ mainly in the respective
coordination number of cations. In the Nd2CuO4 system,
two types of crystal structures are observed namely T/O
and T'. The occurrence of superconductivity in the
Ln2–xCexCuO4–y (Ln = Nd, Pr and Sm) family gives a
new prospect for understanding the attractive forces as
the valence of the Ce dopant suggests that the supercon-
ducting carriers are electrons rather than holes. In most
high temperature superconducting compounds, CuO2
layers are the fundamental structural units, in which the
charge carriers responsible for superconductivity are
localized. It is known that electron correlations play an
important role in determining the physical properties of
these materials. These correlations manifest themselves as
two dimensional magnetic fluctuations, which are due to a
strong super exchange interaction within the CuO2 layers.
The magnetic properties of the Ln2CuO4 (Ln = Nd, Pr,
Eu & Gd) compounds have attracted considerable inter-
est since the discovery of high-temperature superconduc-
tivity in these compounds when doped by Ce [1,2].
These compounds having tetragonal type structure (T'),
in which the Ln3+ and Cu2+ ions are in eightfold and
fourfold coordination respectively [3,4]. The structure of
compounds in the Ln2CuO4 (where Ln = Nd, Pr, Eu, Sm)
system is similar to the compounds in the La based cop-
per oxides [5]. The main difference arises due to the po-
sitions of the oxygen atoms, giving rise to an O2 layer
instead of the La–O layer. The most important feature of
Nd based materials derives the fact that superconductiv-
ity in this system is by electron conduction or n–type
rather than hole conduction as in La based superconduc-
tors. The electron conducting (n–type) compound Nd1.85
Ce0.15CuO4-y with TC = 24 K is the most studied material
in this system [6]. The Nd1.85Ce0.15CuO4-y compound has
the same crystal structure as of Nd2CuO4 [I4/mmm, a =
3.945 Å and c = 12.17 Å] but has slight variation in lat-
tice parameters [a = 3.945 Å and c = 12.076 Å] due to
the substitution of tetravalent Ce in the trivalent Nd lat-
tice [7,8]. It is therefore of high interest to study the
structural characteristics of a divalent dopant (Sr2+) in
Nd2CuO4 system and to assess influence on dielectric and
magnetic properties of defective structures.
In the Nd/Ce–Cu–O system, trivalent Nd3+ is replaced
with tetravalent Ce4+ element which induces n–type su-
perconductivity and crystallizes in two different crystal
structures as mentioned earlier namely T' and T/O. In the
Structural, Magnetic and Dielectric Studies on Strontium Substituted Nd2CuO4 System
Copyright © 2010 SciRes. JMP
present work, Strontium doped Nd2CuO4 system has
been prepared by substituting Strontium (Sr2+) in Neo-
dymium (Nd3+) site inducing excess number of holes in
the system which leads to p–type superconductivity in
the prepared compounds. Structure identification, surface
morphology with composition analysis, magnetic proper-
ties, electron spin resonance and dielectric studies have
been carried out and the results are discussed.
2. Experimental Model
2.1 Sample Preparation
The ceramic compounds Nd2–xSrxCuO4 (where x = 0.05
to 0.2) have been prepared by carefully mixing stoichio-
metric quantities of Nd2O3 (99.9% purity), SrCO3
(99.99% purity) and CuO (99.99% purity) in an agate
mortar with acetone as a mixing medium. Solid state
reaction takes place during successive sintering sessions
in alumina crucibles. The samples were precalcined ini-
tially at 850˚C for 24 hours and the calcined samples
were once again ground thoroughly prior to heating at
900˚C for 24 hours. The final processing of sintering was
done thrice at 925˚C for 24 hours to obtain homogeneity
and then slow cooled at a rate of 5˚C/hour down to
300˚C. These hard sintered samples after final sintering
were well ground and taken for characterization process.
2.2 Powder X – Ray Diffraction
The single phase formation of the compound was con-
firmed through powder XRD patterns which were re-
corded using PANalytical X’Pert PRO Diffractormeter
with CuKα1 radiation (λ = 1.54056 Å). The diffraction data
of the samples were collected with 0.02˚ 2θ steps and 1 sec
count time per step for a 2θ range of 10˚ to 80˚.
2.3 SEM and EDAX
Micro structural surface morphology and elemental com-
position of the prepared compounds were carried out
using Scanning Electron Microscope (SEM) added with
Energy Dispersive X–ray Analysis (EDX) facility. In the
present work, microscopic imaging and energy disper-
sive X–ray analysis (EDX) were simultaneously carried
out using Hitachi S–3400N instrument. The surface of
the pelletized compounds were focused with 5 kV accel-
erating voltage under high vacuum condition.
2.4 Magnetization Studies
The variation in induced magnetic moment with respect
to the applied magnetic field would be identified by Vi-
brating sample magnetometer (VSM) for the analysis of
magnetic nature of the materials. In the present work, the
magnetization experiment was carried out by employing
LAKESHORE Vibrating Sample Magnetometer at room
temperature (300 K) to categorize the magnetic property
of all the prepared compounds.
2.5 Electron Spin Resonance Studies
Interaction of unpaired electron spins with respect to the
external magnetic field yields the electronic nature of the
source material utilized. Electron Spin Resonance (ESR)
or Electron Paramagnetic Resonance (EPR) is a sophis-
ticated spectroscopic technique that detects free radicals
of inorganic complexes by which electronic structure and
magnetic nature may be identified.
In the present work, ESR measurements were carried
out using Varian E-4 spectrometer having X-band fre-
quencies (9.45 GHz). ESR spectra were recorded at room
temperature and all the observations were performed
with approximately 10 mW microwave power incident
upon the sample cavity. The spectrometer was equipped
with an electromagnet capable of producing a stable
magnetic field from 0.001 T up to 0.8 T with the accu-
racy of 0.0001 T. The spectrum is the first derivative
microwave absorption with respect to field (dP/dH). For
each sample, the Hr resonant magnetic field [9] and the
value of peak-to-peak line-width (ΔHpp) was computed
as the difference between the extreme values H1 and H2
of the magnetic field (the maximum and minimum of the
resonance curves, respectively). The resonant magnetic
field (Hr) was computed as (H1+H2)/2. In order to make
better comparative analysis the spectra were recorded by
keeping the instrument settings same for all the samples.
2.6 Dielectric Studies
The study on dielectric constant with respect to the ap-
plied a.c frequency enumerates the nature of the atoms,
ions and its bonding in the material. It is a measure of
polarization in the medium. In the present work, HIOKI
3532–50 LCR HITESTER has been employed for the
analysis of dielectric nature of the prepared compounds
in pelletized form at room temperature condition with in
the frequency range of 50 Hz to 5 MHz. Silver electrode
pasting has been incorporated for to improve the surface
conductivity of the prepared samples.
3. Results and Discussion
3.1 Powder X–ray Diffraction Analysis
The observed powder X–ray diffraction patterns of the pre-
pared polycrystalline samples Nd2CuO4, Nd1.95Sr0.05CuO4–y,
Nd1.9Sr0.1CuO4–y, Nd1.85Sr0.15CuO4–y and Nd1.8Sr0.2CuO4–y
are shown in Figure 1(a) which reveals the single phase
formation of the prepared compounds. Lattice parameters
of the compounds were calculated through AUTOX–93,
a program for auto indexing reflections from multiphase
polycrystals [10]. The comparison of lattice parameters
observed for the prepared compounds with the parent
compound is given in Table 1. The calculated unit cell
parameters shows that the crystal structure of all the pre-
Structural, Magnetic and Dielectric Studies on Strontium Substituted Nd2CuO4 System
Copyright © 2010 SciRes. JMP
pared compounds vary from the parent tetragonal structure
to orthorhombic with least difference in magnitudes. Fig-
ures 1(b) and 1(c) show the shift in the higher intensity
peaks of the prepared compounds with the formation of
newer peaks (marked in * symbol) which reveals variation
in the crystal system and lattice parameters of the prepared
compounds. Due to the substitution of lower atomic radii
element (Sr – 2.45 Å) in the higher atomic radii element
site (Nd – 2.64 Å), the volume of the prepared compounds
decreases with respect to the parent compound. Hence
from the XRD patterns, it may be concluded that the
Neodymium site is partly replaced with the Strontium
3.2 Surface Morphology and Elemental Analysis
The surface morphology and crystallization nature of the
samples were analyzed by scanning electron microscope
images and the observed images for the prepared com-
pounds are shown in Figure 2. In the present work, the
pelletized samples annealed at 925˚C were used for the
surface morphology analysis.
The images of the inner portion of the pellets show
that all the compounds have regular crystallites with the
size in the micrometer range. The regular arrangement of
particles reveals that the compounds were formed in well
crystalline nature without clustering. Some amount of
agglomeration of particles in the parent compound may
be due to low melting point of the same as compared
with Strontium substituted compounds. The elemental
composition analysis confirms the presence of Strontium
in the host matrix of Nd2CuO4 system with increasing
concentrations in the samples. The decrease in the con-
centration of Nd reveals the replacement of trivalent
Neodymium with divalent Strontium element.
3.3 Magnetization Analysis
The observed magnetization nature of the prepared
compounds is shown in Figure 3. It is observed that the
intensity of magnetization varies linearly with the ap-
plied magnetic field for all the prepared compounds
which reveals the paramagnetic nature of the resultant
Table 1. Comparative statement of lattice parameters ob-
served for parent and substituted compounds
Compounda (Å) b (Å) c (Å) Volum
e (Å3)
3.945 3.945 12.17 189.2 T
3.945(3) 3.927(6)12.16(1)188.6 O
3.826(5) 3.943(3)12.19(1)184.1 O
3.832(3) 3.946(2)12.18(6)184.3 O
3.897(6) 3.901(6)12.09(1)183.9 O
* T – Tetragonal and O – Orthorhombic
Figure 1. (a) Powder X–Ray Diffraction patterns of the
prepared compounds; (b) Comparison of diffraction pat-
terns of the major intensity peak; (c) Comparison of dif-
fraction patterns of the 50% intensity peak
Structural, Magnetic and Dielectric Studies on Strontium Substituted Nd2CuO4 System
Copyright © 2010 SciRes. JMP
Figure 2. Surface Morphology and EDX spectrum of the prepared compounds
compounds [11,12]. In the earlier reports, it is identified
that the parent compound Nd2CuO4 exhibits paramag-
netic nature [13] and the same is obtained for both parent
and prepared compounds now. The net magnetic moment
attained by the prepared compounds is in very minimal
level (memu/g) which exhibits the least possible mag-
netization of the prepared compounds and not more sig-
nificant changes on the magnetization nature are ob-
served on substitution of Strontium in Neodymium site.
Hence it is confirmed that all the prepared compounds
Structural, Magnetic and Dielectric Studies on Strontium Substituted Nd2CuO4 System
Copyright © 2010 SciRes. JMP
are exhibiting paramagnetic nature at room temperature.
3.4 ESR Analysis
Figures 4(a) and 4(b) show the room-temperature X-band
(9.45 GHz) ESR spectra of Nd2CuO4 samples with four
different concentrations of Strontium. The room tem-
perature ESR spectrum shows an intense resonance sig-
nal for the Nd2CuO4 and Nd1.95Sr0.05CuO4–y compounds
with both peak to peak line width (ΔHPP) and resonance
field (Hr) that vary depending on the samples. The line
width of the samples was calculated as 0.2852T and
0.2892T for the samples Nd2CuO4 and Nd1.95Sr0.05CuO4–y
respectively. The Lande factor of the samples with sharp
resonance is calculated and the values are 2.37 and 2.33
for Nd2CuO4 and Nd1.95Sr0.05CuO4–y respectively. The
samples with an effective g value of around 2 shows the
paramagnetic behavior which has a good agreement with
results obtained from magnetic measurements (M vs H
curves). Other three samples with higher Strontium con-
centration show no resonance absorption bands. But the
intensity remains constant up to 3000 Gauss and then
decreases exponentially. This condition implies the least
magnetization nature of the prepared samples. The varia-
tion in ΔHPP with respect to Strontium substitution in the
parent system may be due to the presence of inhomoge-
neities and differences in the chemical composition or in
the oxygen stoichiometry [14,15].
3.5 Dielectric Analysis
The dielectric studies have been carried out for the parent
and the strontium substituted compounds. This study
gives experimental values such as capacitance at parallel
and dielectric loss for the frequency range between 50
Hz to 5 MHz at the room temperature for the analysis of
Figure 3. Magnetization nature of the prepared compounds
Figure 4. Electron Spin Resonance nature of the prepared
dielectric behaviour of the prepared compounds. The
dielectric constant was calculated from the formula; εr =
(CP d)/(εo A) where CP is the capacitance in parallel (F),
d is the thickness of the pellet (m) and A is the cross sec-
tional area of the pellet (m2).
The plots of logf versus dielectric constant and dielec-
tric loss have been drawn (Figures 5(a) and 5(b)). It is
observed that the parent compound has the highest di-
electric constant values than the strontium substituted
compounds. It may due to the fact of introduction of
holes in the host Nd2CuO4 system. At the same time,
increasing order of dielectric constant on higher doping
concentration of strontium shows the improved surface
transport properties. The high value of dielectric constant
at low frequencies may be associated with the establish-
ment of polarizations namely; space charge, orientational,
electronic and ionic polarization. The low value of di-
electric constant at higher frequencies may be due to the
loss of significance of these polarizations gradually. The
Structural, Magnetic and Dielectric Studies on Strontium Substituted Nd2CuO4 System
Copyright © 2010 SciRes. JMP
Figure 5. (a) Plots of dielectric constant of the prepared
compounds; (b) Plots of dielectric loss of the prepared com-
frequency dependence of dielectric loss exhibits inter-
esting results. At the lower frequencies, the dielectric
loss reaches the instrumental saturation value (tan δ =
9.9999) but at higher frequencies the value drops down
from this saturation drastically. The low value of dielec-
tric loss at higher frequencies implies that all the samples
possess superior optical quality and shows the possibility
of using the prepared compounds for high frequency
4. Conclusions
In the present work, the effect of partial substitution
on Neodymium site in Nd2CuO4 system with Strontium
was carried out. The ceramic compounds Nd2CuO4,
Nd1.95Sr0.05CuO4–y, Nd1.9Sr0.1CuO4–y, Nd1.85Sr0.15CuO4–y
and Nd1.8Sr0.2CuO4–y were prepared by solid state reac-
tion technique with high purity chemicals. Structural
characterization was carried out by using powder X–ray
diffraction technique and it was found that the parent
compound crystallized in tetragonal structure and the
other newly prepared compounds were crystallized in
orthorhombic structure. Surface morphology confirms
the high crystalline nature of the prepared compounds
whereas increasing order of Strontium in the Nd2CuO4
system is confirmed through elemental compositions
using energy dispersive analysis. The magnetic nature of
the compounds was identified with vibrating sample
magnetometer and it was found that both parent and
prepared compounds exhibit paramagnetic nature at
room temperature. Increasing concentration of Strontium
in the Nd2CuO4 system results in the decrease in net
magnetization of all the prepared compounds. The same
results are also identified in the electron paramagnetic
resonance studies through the least resonance absorption
intensity of the parent and the prepared compounds. In-
crease in dielectric constant on higher doping concentra-
tion confirms the incorporation of Strontium in the
Nd2CuO4 system and the least value of dielectric loss at
higher frequencies confirms the improved surface trans-
port properties of the prepared compounds.
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