Particle size dependence on the structural, transport and optical properties of charge-ordered Pr0.6Ca0.4MnO3

Article abstract of DOI:10.1016/j.jallcom.2015.07.160

Abstract Structural, transport and optical properties of nano-crystalline Pr_0.6Ca_0.4MnO₃ have been investigated to emphasize on the semiconducting properties of charge-ordered manganite. Rietveld refinement of X-ray diffraction pattern of Pr_0.6Ca_0.4MnO₃ nanoparticles show that due to increase in sintering temperature, MnO₆ octahedra elongated along z-direction and compressed in x-y plane. Both Mn-O-Mn angles are found to decrease with increasing sintering temperature. Fourier transform infrared (FTIR) spectroscopy measurements reveal that the stretching and bending vibration of Mn-O-Mn is responsible for the change in Mn-O-Mn bond length and bond angle respectively. With increasing sintering temperature, these vibrations tend to increase, which resulted in the further distortion of MnO₆ octahedra. Magnetic measurements suggest that charge ordering is established and system becomes antiferromagnetic with increasing particle size. Resistivity behavior of Pr_0.6Ca_0.4MnO₃ nanoparticles clearly exhibit semiconducting nature of these systems, which is due to the formation of charge-ordered state of Mn³⁺ and Mn⁴⁺. Estimated optical band-gap of ～3.7 eV for Pr_0.6Ca_0.4MnO₃ nanocrystals, makes it a potential candidate for wide band-gap magnetic semiconductors.

Full text of DOI:10.1016/j.jallcom.2015.07.160

Accepted Manuscript
Particle size dependence on the structural, transport and optical properties of charge-
ordered Pr Ca MnO
0.6 0.4
3
Satyam Kumar, G.D. Dwivedi, J. Lourembam, Shiv Kumar, U. Saxena, A.K. Ghosh,
H. Chou, Sandip Chatterjee
PII:
S0925-8388(15)30557-0
10.1016/j.jallcom.2015.07.160
JALCOM 34853
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 5 April 2015
Revised Date: 26 June 2015
Accepted Date: 19 July 2015
Please cite this article as: S. Kumar, G.D. Dwivedi, J. Lourembam, S. Kumar, U. Saxena, A.K.
Ghosh, H. Chou, S. Chatterjee, Particle size dependence on the structural, transport and optical
properties of charge-ordered Pr Ca MnO , Journal of Alloys and Compounds (2015), doi: 10.1016/
0.6 0.4
3
j.jallcom.2015.07.160.
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ACCEPTED MANUSCRIPT
Graphical Abstract
3
2
0.9
0.6
Pr0.6Ca0.4MnO3
T = 5 K
1000 o
C
1
Eg=3.47 eV
600
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0.3
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T = 5 K
800 o
C
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Energy (eV)

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Particle size dependence on the structural, transport and optical
properties of charge-ordered Pr0.6Ca0.4MnO3
Satyam Kumar,a G. D. Dwivedi,a,b J. Lourembam,c,d Shiv Kumar,a U. Saxena,a A. K. Ghosh,a H.
Chou,b and Sandip Chatterjeed,*
aDepartment of Physics, Banaras Hindu University, Varanaasi-221005, India
bDepartment of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
cDivision of Physics and Applied Physics, School of Physical and Mathematical Sciences,
Nanyang Technological University, Singapore 637371, Singapore
dDepartment of Physics, Indian Institute of Technology (Banaras Hindu University), Varanasi-
221005, India
*Corresponding author e-mail id: schatterji.app@iitbhu.ac.in
Abstract
Structural, transport and optical properties of nano-crystalline Pr0.6Ca0.4MnO3 have been
investigated to emphasize on the semiconducting properties of charge-ordered manganite.
Rietveld refinement of X-ray diffraction pattern of Pr0.6Ca0.4MnO3 nanoparticles show that due to
increase in sintering temperature, MnO6 octahedra elongated along z-direction and compressed
in x-y plane. Both Mn–O–Mn angles are found to decrease with increasing sintering temperature.
Fourier transform infrared (FTIR) spectroscopy measurements reveals that the stretching and
bending vibration of Mn–O–Mn is responsible for the change in Mn–O–Mn bond length and
bond angle respectively. With increasing sintering temperature, these vibrations tend to increase,
which resulted in the further distortion of MnO6 octahedra. Magnetic measurements suggest that
charge ordering is established and system becomes antiferromagnetic with increasing particle
size. Resistivity behavior of Pr0.6Ca0.4MnO3 nanoparticles clearly exhibit semiconducting nature
of these systems, which is due to the formation of charge-ordered state of Mn3+ and Mn4+.
Estimated optical band-gap of ~ 3.7 eV for Pr0.6Ca0.4MnO3 nanocrystals, makes it a potential
candidate for wide band-gap magnetic semiconductors.
Key-Words: Manganites; Wide band-gap semiconductors; Charge-ordering; Nano-materials
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1. Introduction
Hole doped perovskite manganites, R1-xAxMnO3, with orthorhombic crystal structures
(where, R represents rare earth elements and Arepresents divalent alkaline earth elements) have
attracted much attention mainly due to the vastand unprecedented physical properties they
exhibit [1–3]. Charge ordering (CO) of Mn3+ and Mn4+ions, a representative phenomenon of
these manganite materials, is a consequence of the dominant Coulomb interaction over the
kinetic energy of the charge carriers [4]. The charge ordering phenomenon has been observed
mostly when the concentration of charge carriers takes a rational value of the periodicity of the
crystal lattice [5,6]. It has been shown that in a crystal, which favors an antiferromagnetic
insulating phase, the charge ordered phase often competes with a ferromagnetic metallic phase
and can be melted to the ferromagnetic metallic phase by the introduction of some external
forces, such as a magnetic field, a high pressure, an exposure to laser radiation, even an electrical
field or some internal strain induced by chemical substitution [7–11].
Manganite materials have been the subject of intense research because of differing
properties of nanostructures from their bulk counterparts and their great potential technological
application, including sensing devices, ferrofluids, magneto-tunable photocurrent devices, Spin
Hall-Magnetoresistive devices and many more [12-20]. Doped perovskite manganites exhibit
strong dependence of their properties on the particle size of the systems, especially on the charge
ordered state. Evidence of the suppression of the antiferromagnetic charge ordered state in the
Pr0.5Sr0.5MnO3 and Nd0.5Sr0.5MnO3 nanoparticles was obtained [21,22]; the charge ordered and
antiferromagnetic phase transition observed in thebulk Nd0.5Ca0.5MnO3 disappeared in the
nanoparticles and ferromagnetic metallic phase emerged [23].The strong charge ordered state in
bulk Pr0.5Ca0.5MnO3, where a strong magnetic field is necessary to suppress the charge ordered
antiferromagnetic insulating phase and to develop ferromagnetic metallic phase, has also been
reported to be suppressed in both Pr0.5Ca0.5MnO3 nanoparticles and nanowires [24,25].So from
these reports, it has been observed that the reduction of particle size can suppress the formation
of the CO state. However, this conclusion is not applicable to all the CO systems. Biswas et al.
observed charge ordering in nanocrystalline Pr0.65Ca0.35MnO3 [26], which was obviously
contradictory to the situation of Pr0.5Ca0.5MnO3nanoparticles though the two compounds in bulk
form show the same generic behavior. This result is quite in agreement with the reports of
La0.4Ca0.6MnO3 systems, where the disappearance of charge orderedstate in nanoparticles was
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reported by Lu et al. [27], but later an opposite result of the enhanced stability ofthe
antiferromagnetic charge ordered ground state in La0.4Ca0.6MnO3 with a particle sizeof 17 nm
was reported [28].It seems that whether the reduction of the particle size can suppress the CO or
not is still disputed and needs further investigation.
It is a well-studied fact that Pr1-xCaxMnO3 shows charge-ordered antiferromagnetic
insulating phase for 0.3 ≤ x ≤ 0.5. But, this charge ordered antiferromagnetic state can be
suppressed by reducing the particle size [29]which leads to coexistence of canted
antiferromagnetic and ferromagnetic state. Because of semiconducting nature of this charge
ordered antiferromagnetic-ferromagnetic state these systems can be useful for the magnetic
semiconductor devices.In this work, we have prepared Pr0.6Ca0.4MnO3 nanoparticles with
varying particle size by sintering at three different temperatures (600 ºC, 800 ºC and 1000 ºC)
and studied its structural, transport and optical properties. Idea is to investigate the effect of
particle size on the band-gap of semiconducting Pr0.6Ca0.4MnO3 nanostructures. Exploring the
optical behavior of these charge-ordered antiferromagnetic semiconductors may provide
opportunity to apply these manganite materials in the area of magnetic semiconducting devices.
2. Experimentaldetails
To synthesized Pr0.6Ca0.4MnO3 nanoparticles, stoichiometric amount (0.6 mol: 0.4 mol) of
as purchased Pr6O11 and CaCO3 powders were dissolved in 40 ml nitric acid and mixed for 30
minutes. Equimolar amount of thus obtained metal nitrates and Mn(NO3)3.4H2O were mixed
together in aqueous solution of citric acid, to obtain a homogeneous precursor solution. Ethylene
glycol was added in the solution while stirring. Metal nitrates, ethylene glycol and citric acid
were taken in 1:3:4 molar ratio, respectively. The precursor solution was heated at 90°C till the
formation of xerogel. The obtained xerogel was dried in oven at 200°C for 12 hrs and then
swelled xerogel was kept at 300° C for 5 hrs to complete evaporation of liquid phases. The dried
xerogel were ground into powder and then were sintered at 600, 800, 1000° C for 5 hrs. Prepared
nanoparticles have been abbreviated as PCMO6, PCMO8 and PCMO10 respectively. Phase
formation of as prepared Pr0.6Ca0.4MnO3 samples were confirmed with Rigaku Miniflex-II
DEXTOP X-ray diffractometer using CuKα radiation (λ = 1.5406 Å).Transmission electron
microscopy (TEM)measurements were done with Tecnai G2 S-Twin (FEI, The Netherlands).
Fourier transform infrared (FTIR) spectroscopy measurements were performed with FTIR
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spectrometer (Spectrum One, Perkin Elmer Instrument, USA) in the range of 4000–400 cm-1 with
a resolution of 1 cm-1. Magnetic measurements were done with VSM-SQUID magnetometer.
Resistivity measurements were done via 2-probe method using Keithley 2400 sourcemeter. Two
electrodes were prepared with silver paste on the opposite sides of circular disc. The optical
absorption spectra were measured in the range of 300–800 nm using UV-Vis spectrometer
(Perkin Elmer Instrument, Lamda-25, USA).
3. Results and Discussion
3.1.Structural analysis
Phase purity of PCMO nanoparticles have been checked with their X-ray diffraction
patterns (Fig.1). Rietveld refinement of X-ray diffraction pattern of each sample has been carried
out considering Pbnm space group using Fullprof suite program. The red circles represent
observed X-ray diffraction pattern and the black line going through the red circles represents
calculated pattern of Pbnm space group model. Blue horizontal line in the bottom shows the
difference between observed and calculated pattern. Green vertical bars represent allowed
Bragg’s reflection peaks. As one can see that the observed X-ray diffraction data of all the three
samples are fitted well with Pbnm space group model which suggests that each sample has been
crystallized in orthorhombic Pbnm space group without any secondary or impurity phases.
Refined parameters have been given in Table 1. Lattice volume of PCMO6, PCMO8, PCMO10
increases with increasing sintering temperature (Table 1). In MnO6 octahedra, all the six Mn–O
bonds are not equivalent, Mn–O bonds directed along z-direction are significantly bigger than
bonds in x-y plane; resultantly the MnO6 octahedra gets distorted. Here it should be understood
that the calculated distortion in the MnO6 octahedra have some limitations and there might have
some error due to the limitations in resolution of X- ray powder diffractometer. With increasing
the sintering temperature, Mn–O bonds elongated more along the z-direction and compresses in
x-y plane (Table 1), which shows increase in Jahn-Teller distortion (Fig.2). Average crystallite
size of PCMO6, PCMO8 and PCMO10 calculated from Scherrer’s equation comes around 21
nm, 26 nm and 30 nm respectively.
To know the morphology and microstructure of nano-crystalline Pr0.6Ca0.4MnO3 surface,
low-resolution transmission electron microscopy (TEM) measurements have been performed.
TEM images of these samples show almost irregular granular shape. Due to the suppression of
antiferromagnetic ordering in nano-regime the effective magnetic moment increases and because
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of this increased magnetic moment nanoparticles are strongly agglomerated with each other to
make irregular sizes and shapes which makes it rather difficult to separate them. Estimated
average grain sizes of three samples sintered at 600°C, 800°C and 1000°C comes about 36 nm,
38 nm and 42 nm respectively, which is consistent with the X-ray diffraction results of increase
in crystallite sizes with increasing sintering temperature (Fig.3(a, c & e)). Selected area electron
diffraction (SAED) image shows the increase of crystalline nature of Pr0.6Ca0.4MnO3 system with
increase of sintering temperature (Fig.3(b, d & f)). Pr0.6Ca0.4MnO3 sintered at 1000°C shows
much clearer and brighter Bragg’s spots than rest of the two systems sintered at 600°C and
800°C, which guides us to realize better crystalline nature of this system. To further check the
crystalline nature of Pr0.6Ca0.4MnO3 nanoparticle with increasing particle size, we have examined
the TEM and SAED images of Pr0.6Ca0.4MnO3 sintered at 1200°C (figures not shown). TEM
image shows that after sintering at 1200°C particle size becomes 130 nm and system corresponds
to bulk material. X-ray diffraction, low-resolution TEM and SAED measurements have
confirmed single phase nature of our samples with almost homogeneous distribution. Electron
dispersive X-ray spectra (EDS) of as prepared Pr0.6Ca0.4MnO3 samples have been presented in
Fig.4. Elemental composition (weight % and atomic %) presented in Table 2 show that samples
are in desired stoichiometric proportions. EDS also provides the information that there is no
oxygen deficiency present in these systems.
3.2. Fourier transform infrared spectroscopy
We have probed Fourier transform infrared (FTIR) spectroscopy technique to investigate
about the functional species and lattice vibration present in our systems (Fig.5). In finger-print
region, the band arising from 490-750 cm-1 corresponds to characteristic Mn–O bond (stretching
and bending). This confirms that each sample strongly contains the Mn–O bond and due to the
internal motions, bond length and bond angle of Mn–O–Mn changes, which is responsible for the
band formation. Stretching vibration of Mn-O bond (range 490-600 cm-1) is responsible for the
change in Mn–O–Mn length, while the bending vibration (600-750 cm-1) involves the change of
Mn–O–Mn bond angle. With increasing sintering temperature, these vibrations tend to increase,
which resulted in the further distortion of MnO6 octahedra. The band around 1400 cm-1 (1370-
1440 cm-1) and wide band around 1640 cm-1 correspond respectively to antisymmetric stretching
-
and water bending mode of hydrated NO3 ions [30] (which formed in the solution and may
present on the surface of nano-crystals).
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3.3. Magnetic Property
To get the information about the charge-ordered state in Pr0.6Ca0.4MnO3 and its impact on
the magnetic properties, VSM-SQUID magnetometer have been probed. Magnetization versus
temperature (M-T) measurements have been done with Zero field cooling (ZFC) and field
cooling (FC) condition under 100 Oe magnetic field [Figures: 6(a), 6(b) &6(c)]. M-T
measurements of PCMO6, PCMO8 and PCMO10 show a broad peak around 230 K, which
indicates establishment of charge-ordering (CO) in the system. The charge ordering is increasing
with sintering temperature. This increase in charge-ordering with increasing particle size is found
in accordance with the other manganite systems [21-25, 31]. To get the clear picture about
charge-ordering of Pr0.6Ca0.4MnO3 nanocrystals, we have plotted the 1/χ versus T from FCW
curve (figures: 6(a), 6(b) &6(c)). At higher temperatures, 1/χ versus T curve follows the Curie-
Weiss law and Curie-Weiss fitting provided Weiss constant (Θ) ~ 145 K for each systems. As it
is clear from these plots, 1/χ starts to deviate from Curie-Weiss law around 230 K. This deviation
of 1/χ towards lower temperature side is due to the reduced magnetic moment, which is an
indication of the onset of AFM-CO states. This deviation is stronger in PCMO10, but it is still
quite evident in PCMO6 and PCMO8. These results have established that the AFM-CO states
have been induced in Pr0.6Ca0.4MnO3 systems. Non-saturating M-H hysteresis curves of
Pr0.6Ca0.4MnO3 indicate the competition between antiferromagnetic and ferromagnetic phases of
these systems at low temperature [figures: 6(d)]. PCMO6 shows higher magnetic moment and
clear hysteresis behavior, while for PCMO8 and PCMO10 magnetic moment decreases and
hysteresis gradually diminishes. This indicates that with increasing particle size, charge-ordered
states became prominent, which led to antiferromagnetic ordering. Magnetic properties clearly
establish the induction of charge ordered states with increasing particle size.
3.4. Resistivity Measurement
Pr0.5Ca0.5MnO3 shows charge ordered type insulating behavior down to low temperature [26].The
charge ordering arises due to the competition between double exchange interaction and super-
exchange interaction of Mn- core spins and Coulomb interaction among electrons of distinct
orbitals of the same Mn-site [32,33]. Resistivity behavior of PCMO6, PCMO8 and PCMO10
systems have been studied as a function of temperature in Fig.7. Pr0.6Ca0.4MnO3 systems show
semiconducting behavior throughout the measured temperature range. This semiconducting
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behavior is due to the formation of charge-ordered state in Pr0.6Ca0.4MnO3 nano-systems. The
transport properties of nanoparticles depend on the particle size and significantly affected by the
grain boundaries of nano-crystalline system. X-ray diffraction analysis and low-resolution
transmission electron microscopy analysis show that particle size is increasing with increase in
sintering temperature. With increase in particle size, resistivity of systems decreases, which
might be due to the fact that with increasing particle size, the grain boundaries become less and
hence the charge carriers experience less restriction. The semiconducting properties in
manganites can also arise due to the presence of oxygen deficiency. But, as we have already seen
from EDS results that there is no signature of oxygen deficiency in present systems and hence it
is not playing any role in semiconducting behavior of Pr0.6Ca0.4MnO3 nano-crystals.
Resistivity behavior of PCMO6, PCMO8 and PCMO10 have been fitted with
ρ=ρ0exp(Ea/kBT) for nearest-neighbour hopping of small polarons (Fig.8) where, kB is the
Boltzmann’s constant and Ea is the activation energy. Calculated activation energy (Ea) have
been presented in Table 3. Resistivity and activation energy both decrease with increasing
annealing temperature. The linear fit of high temperature region indicates that conduction in this
region is dominated by thermally activated polarons. At low temperature, thermal activation
mechanism is not valid as shown by the deviation of curve. Instead of that, variable-range-
hopping (VRH) conduction of polarons has been found to dominate in low temperature region.
The conduction mechanism due to the VRH of polarons can be stated by the Mott’s equation
[34-36] ρ(T)=ρ0exp[T0/T]1/4 where, ρ0 and T0 are constants and are given by
ρ0={[8παkBT/N(EF)]1/2}/(3e2νph) and T0=18α3/[kBN(EF)] where, νph (~1013 s−1) is the phonon
frequency at Debye temperature, N(EF) is the density of localized electron states at the Fermi
level, and α is the inverse localization length. These equations lead to a linear relation between
ln(ρT−1/2) versus (1/T)1/4 graph for VRH conduction. The linear fit of ln(ρT−1/2) versus (1/T)1/4
graph (see inset Fig.8) establishes that below a certain temperature Th, conduction mechanism is
dominated via variable range hopping (VRH). The Th values for PCMO6, PCMO8 and PCMO10
are 124 K, 115K and 109K, respectively. The average hopping distance (R) and average hopping
energy (Eh) at 150 K have been calculated from R = [9/8παkBTN(EF)]1/4 and Eh= 3/[4πR3N(EF)].
Alternatively, two conditions (i) αR > 1 and (ii) Eh> kBT [37] are responsible and should be
followed for VRH conduction. All the three samples are following above mentioned conditions
as shown in Table-2. It is very important to mention that while fitting the resistivity data of
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polycrystalline Pr0.6Ca0.4MnO3, we have ignored the contribution from grain boundary effect of
nanoparticles and have focused on intrinsic behavior of manganite systems. Variation in particle
size cannot change the density of states at Fermi level, which could have been responsible for the
large decrease of T0. Instead of that, increase of localization length α-1 which favors electronic
delocalization, can be responsible for the observed suppression of T0.
3.5. Ultraviolet-Visible spectroscopy
Optical absorbance has been studied and optical band-gap have been estimated for
Pr0.6Ca0.4MnO3 by using Ultraviolet-Visible (UV-Vis) spectroscopy (Fig.9). UV-Vis spectra of
all the three samples display three different characters ranging from ultraviolet to infrared region.
A sharp absorption near 300 nm (ultraviolet region) followed by exponential decay region near
absorption edge (ultraviolet to visible region) and then a smooth extended region (visible to
infra-red region). The optical absorption edge can be analyzed by relation given below [38],
ꢀꢁꢂ ∝ ꢃꢁꢂ ꢄ ꢅꢆꢇꢈ
where, n can acquire value, ½ and 2 for direct and indirect type of transitions
respectively, while absorption coefficient ‘α’ depends upon the optical absorbance (A) and
thickness (d);
ꢋ
ꢀꢃꢂꢇ ꢉ 2.303 ꢊ ꢃ ꢍ ꢇ
ꢌ
(αhν)2 versus hν plot for PCMO6, PCMO8 and PCMO10 have been presented in Fig.10.
Linear variation of (αhν)2 as a function of photon energy (hν) for wide range, suggests direct type
of transition in these systems. The intercepts of these plots on the energy axis provide the optical
band-gap of systems. Optical band-gaps of PCMO6, PCMO8 and PCMO10 from these plots are
3.68 eV, 3.63 eV and 3.47 eV respectively. The decrease in band-gap with increasing sintering
temperature can be attributed to the increased particle sizes which have been related to decreased
resistivity of the systems. Earlier reported band-gap of manganites are well below than the band-
gap observed in this system [39,40]. The observed band-gaps of these systems comes in wide
band-gap semiconductors region and these band-gaps are even wider than the reported wide
band-gaps of ZnO (3.37 eV) and GaN (3.44 eV) [41,42]. After sintering at 1200°C, optical band-
gap of Pr0.6Ca0.4MnO3 system increases drastically and becomes almost insulator (figure not
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shown). Additionally, manganite systems endow much better magnetic ordering and magnetic
moment than any known diluted magnetic semiconductors. With the magnetic behavior they
possess as well as semiconducting nature of studied manganite material can prove it’s worth as a
magnetic semiconductor material and can prove pivotal in the field of semiconductor spintronics.
4. Conclusion
Structural measurements (X-ray diffraction, low-resolution TEM and SAED
measurements) provide information regarding the phase formation and nano-crystalline nature of
our Pr0.6Ca0.4MnO3 systems. Rietveld refinement of X-ray diffraction pattern of Pr0.6Ca0.4MnO3
nanoparticles reveals elongation in Mn–O bonds along z-direction and compression in Mn–O
bonds in x-y plane, with increasing sintering temperature. Both Mn–O–Mn angles are found to
decrease with increasing sintering temperature. Crystallite size and grain size calculated from
XRD and TEM respectively, confirms nano-crystalline structure of our systems. SAED images
show, system becomes more crystalline with increasing sintering temperature. FTIR
measurement confirms the presence of characteristic Mn–O stretching vibration mode near 600
cm-1, which is responsible for the structural distortion, magnetic and transport properties of this
system. Magnetization behavior clearly demonstrates the antiferromagnetic charge ordering in
the systems. Resistivity measurement shows that due to the presence of Pr in A-site, systems
behave like charge ordered semiconductor. UV-Vis measurement confirms the semiconducting
nature of our Pr0.6Ca0.4MnO3 nanocrystals with band-gap of ~ 3.5 - 3.7 eV, which falls in wide
band-gap semiconductor range. The wide band-gap semiconducting behavior along with their
already well known magnetic properties, makes Pr0.6Ca0.4MnO3 nanoparticles a suitable
candidate for magnetic semiconductor device applications.
Acknowledgement
SC is grateful to the funding agencies DST (Grant No.: SR/S2/CMP-26/2008), CSIR (Grant No.:
03(1142)/09/EMR-II) and BRNS, DAE (Grant No.: 2013/37P/43/BRNS) for financial support.
Satyam Kumar is grateful to UGC for financial support. Authors gratefully acknowledge Prof.
O.N.Srivastava, Prof. P.C.Srivastava and Bio-physics lab, BHU for their help in providing
experimental facilities for TEM, UV-Vis and FTIR respectively.
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Figure Captions:
Fig.1 Rietveld refinement of X-ray diffraction pattern of Pr0.6Ca0.4MnO3 nanoparticles sintered at
600°C, 800 °Cand 1000 °C.
Fig.2 Schematic diagram of distorted MnO6octahedra of Pr0.6Ca0.4MnO3sintered at 600°C and
1000°C.
Fig.3 Low-resolution transmission electron microscopy images of Pr0.6Ca0.4MnO3 nanoparticles
sintered at 600°C (a), 800°C (c) and 1000°C (e); selected area electron diffraction images
of Pr0.6Ca0.4MnO3 nanoparticles sintered at 600°C (b), 800°C (d) and 1000°C (f).
Fig.4 Electron dispersive X-ray spectra (EDS) of Pr0.6Ca0.4MnO3nanoparticles sintered at 600°C,
800°C, and 1000°C have
Fig.5 Fourier transform infrared spectroscopy of Pr0.6Ca0.4MnO3 nanoparticles sintered at 600°C,
800°C and 1000°C.
Fig.6 Zero field cooled (ZFC) and field cooled (FC) magnetization (M-T) measurement of
Pr0.6Ca0.4MnO3 nanoparticles sintered at (a) 600°C, (b) 800°C and (c) 1000°C at 100 Oe
magnetic field. M-H hysteresis loop of Pr0.6Ca0.4MnO3 nanoparticles sintered at 600°C,
800°C and 1000°C at 5 K.
Fig.7 Variation of resistivity with temperature of Pr0.6Ca0.4MnO3nanoparticles sintered at 600°C,
800°C and 1000°C.
Fig.8 Variation of ln(ρ) as function of 1000/T for Pr0.6Ca0.4MnO3 nanoparticles sintered at
600°C, 800°C and 1000°C at low temperature region (respectively, for T>124K, 115K
and 109K). Inset: ln(ρT-1/2) vs. T-1/4 at lower temperature region (respectively, for
T<124K, 115K and 109K). The linear fit indicates the variable range hopping conduction
is active in this temperature range.
Fig.9 Ultraviolet-visible spectra of Pr0.6Ca0.4MnO3 nanoparticles sintered at 600°C, 800°C and
1000°C.
Fig.10 Variation of (αhν)2 versus photon energy ‘hν’ for Pr0.6Ca0.4MnO3 nanoparticles sintered at
600°C, 800°C and 1000°C.
12

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Table 1. Selected refined parameters (lattice parameters, lattice volume, Wyckoff’s positions,
bond-length and bond-angles) of Pr0.6Ca0.4MnO3 sintered at 600oC, 800oC and 1000oC.
Sample
Pr0.6Ca0.4MnO3
Pr0.6Ca0.4MnO3
Pr0.6Ca0.4MnO3
sintered at 600 oC
sintered at 800 oC
sintered at 1000 oC
a (Å)
b (Å)
5.391(3)
7.6563(15)
5.382(2)
5.4385(14)
7.6344(15)
5.4091(14)
224.5842
5.4301(11)
7.6449(10)
5.4147(11)
224.7782
c (Å)
Volume (Å3)
222.1427
x
y
z
x
y
z
x
y
0.03250
0.25000
0.01548
0.00000
0.00000
0.00000
0.27977
0.02791
0.654(4)
0.51240
0.25000
-0.013(16)
2 × 1.7342
2 × 1.9165
2 × 2.2188
148.7(6)
0.03250
0.25000
0.01548
0.00000
0.00000
0.00000
0.27977
0.02791
0.665(6)
0.51240
0.25000
0.025(12)
2 × 1.7768
2 × 1.9146
2 × 2.1825
151.1(9)
0.03250
0.25000
0.01548
0.00000
0.00000
0.00000
0.27977
0.02791
0.623(7)
0.51240
0.25000
0.024(6)
2 × 1.6724
2 × 1.9168
2 × 2.3752
142.0(9)
Pr/Ca
Mn
O1
z
x
y
O2
z
Octahedral
site
Mn-O
(Å)
Mn-O1-Mn (deg)
Mn-O2-Mn (deg)
174.21(14)
170.95(18)
171.24(10)
Table 2.Electron dispersive X-ray spectroscopy (EDS) measurement of Pr0.6Ca0.4MnO3
nanoparticles sintered at 600 °C, 800 °Cand 1000 °Cprovides the elemental composition of
synthesized compounds.
Sample
600 °C
800 °C
1000 °C
Element % Weight %
Atomic %
14.34
4.96
Weight % Atomic % Weight % Atomic %
Pr
Ca
Mn
O
47.3
4.66
23.53
22.99
1.53
44.55
5.43
12.85
5.51
47.62
5.86
14.50
6.28
18.30
61.37
1.03
23.63
24.89
1.50
17.47
63.21
0.96
23.82
22.57
0.12
18.60
60.53
0.08
Cu
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Table 3.Values of various parameters of variable-range-hopping mechanism of Pr0.6Ca0.4MnO3
and activation energy from small polaron theory.
Samples
T0 (K)
α (cm−1)
(inverse
localization
length)
R (cm)
Activation
Energy(eV)
(From SPT) Eh(eV)
Hopping
Energy
(average
hopping
distance)
(From
VRH)
6.313×106
3.209×107
8.994×107
2.648×108
1.368×109
1.498×1015
2.378×10-5
5.000×10-10
6.984×10-13
3.21×10-2
Pr0.6Ca0.4MnO3
sintered at 600 oC
Pr0.6Ca0.4MnO3
sintered at 800 oC
Pr0.6Ca0.4MnO3
sintered at 1000 oC
0.1113
2.88×10-2
1.84×10-1
0.1063
0.0963
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Fig. 1
15

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Fig. 2
16

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Fig.3
17

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Pr0.6Ca0.4MnO3 Sintered at 800 °C
Pr Ca MnO Sintered at 1000 °C
Pr00..66Ca00..44MnO33 Sintered at 600 °C
Fig.4
18

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Pr0.6Ca0.4MnO3
600 oC
Mn-O
NO3-
800 oC
1000 oC
400 800 1200 1600 2000 2400 2800 3200 3600 4000
Wavenumber (cm-1)
Fig.5
19

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0.14
5000
4000
3000
2000
1000
0
Pr0.6Ca0.4MnO3 sintered at 800 oC
Pr0.6Ca0.4MnO3 sintered at 600 oC
0.18
0.15
0.12
0.09
0.06
0.03
0.00
6000
4000
2000
0
0.12
0.10
0.08
0.06
0.04
0.02
ZFC
FC
ZFC
FC
100 Oe
100 Oe
TCO ~ 230 K
(b)
TCO ~ 230 K
(a)
Θ
= 151 K
Θ
= 144 K
0
50
100
150
200
250
300
0
50
100
150
T (K)
200
250
300
T (K)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
5000
4000
3000
2000
1000
0
Pr0.6Ca0.4MnO3 sintered at 1000 oC
0.9
0.6
Pr0.6Ca0.4MnO3
T = 5 K
ZFC
FC
600
800
1000
100 Oe
0.3
0.4
0.0
T = 5 K
TCO ~ 230 K
0.2
0.0
-0.3
-0.6
-0.9
(d)
600
800
1000
-0.2
-0.4
(c)
Θ
= 158 K
-0.9 -0.6 -0.3 0.0
0.3
0.6
0.9
H (Tesla)
0
50
100
150
200
250
300
-5 -4 -3 -2 -1
0
2
3
4
5
H (Tesl1a)
T (K)
Fig.6
20

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3.0x104
2.5x104
2.0x104
1.5x104
1.0x104
6000C
8000C
10000C
Pr0.6Ca0.4MnO3
5.0x103
0.0
100
150
200
250
300
Temperature (K)
Fig.7
21

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Pr0.6Ca0.4MnO3
Sintered at 6000C
10
8
8
6
6
4
T ~ 124 K
2
0
4
-2
2
0.24
0.26
0.28
0.30
0.32
0.34
-1/4
(1/T)1/4(K
)
2
4
6
8
10
12
14
1000/T (K-1)
4.5
Pr0.6Ca0.4MnO3
Sintered at 800 oC
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
8
6
T ~ 115 K
4
2
0
-2
0.24
0.26
0.28
(1/T)1/4(K
0.30
0.32
0.34
-1/4
)
2
4
6
8
10
12
14
1000/T (K-1)
Pr0.6Ca0.4MnO3
Sintered at 1000 oC
10
8
8.2
8.0
7.8
7.6
7.4
7.2
7.0
6
T ~ 109 K
4
0.315
0.320
0.325
0.330
(1/T)1/4(K-1/4
0.335
0.340
0.345
0.350
2
)
2
4
6
8
10
12
14
16
18
1000/T (K-1)
Fig.8
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Pr0.6Ca0.4MnO3
600 oC
800 oC
1000 oC
300
400
500
600
700
800
Wavelength (nm)
Fig.9
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3
2
1000 oC
1
Eg=3.47 eV
0
1.6
2.0
2.4
2.4
2.4
2.8
2.8
2.8
3.2
3.2
3.2
3.6
4.0
4.0
4.0
0.6
0.4
0.2
800 oC
3.6
Eg=3.63 eV
0.0
1.0
1.6
2.0
600 oC
0.5
0.0
Eg=3.68 eV
1.6
2.0
3.6
Energy (eV)
Fig.10
24

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Highlights:
∑ Pr0.6Ca0.4MnO3 nanoparticles have been synthesized via sol-gel route.
∑ Optical properties of charge-ordered Pr0.6Ca0.4MnO3 have been investigated.
∑ Pr0.6Ca0.4MnO3 nanoparticles exhibit wide band-gap (3.7 eV) semiconducting nature.
∑ Potential candidate for wide band-gap magnetic semiconductor device applications.