The effect of different synthesis techniques on structural, microstructural and electrical properties of La0.7Sr0.3MnO3 (LSMO) was investigated. Two different techniques viz solid state reaction (SSR) and sol-gel (SG) method were used to prepare the samples. X-ray studies have confirmed the single phase formation of LSMO by both the techniques. The average grain size was 2 m for solid state reaction sample and 22 nm for sol-gel sample. A substantial enhancement in electrical resistivity was observed in the sample with nanosized grains. The micro grain size sample exhibited metallic behaviour whereas nanoparticle sample showed metal-insulator transition around 250 K.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3554

Reshi, Hilal Ahmad

Shelke, Vilas

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 4, 04053(3pp) (2013) Том 5 № 4, 04053(3cc) (2013) 
 
 
2077-6772/2013/5(4)04053(3) 04053-1  2013 Sumy State University 
Grain Size Induced Metal-insulator Transition in La0.7Sr0.3MnO3 Compounds 
 
Hilal Ahmad Reshi, Vilas Shelke* 
 
Novel Materials Research Laboratory, Department of Physics, Barkatullah University, Bhopal (M.P.) India 
 
(Received 23 August 2013; published online 31 January 2014) 
 
The effect of different synthesis techniques on structural, microstructural and electrical properties of 
La0.7Sr0.3MnO3 (LSMO) was investigated. Two different techniques viz solid state reaction (SSR) and sol-
gel (SG) method were used to prepare the samples. X-ray studies have confirmed the single phase for-
mation of LSMO by both the techniques. The average grain size was 2 m for solid state reaction sample 
and 22 nm for sol-gel sample. A substantial enhancement in electrical resistivity was observed in the sam-
ple with nanosized grains. The micro grain size sample exhibited metallic behaviour whereas nanoparticle 
sample showed metal-insulator transition around 250 K. 
 
Keywords: Nanomaterials, Manganites, Metal-insulator transition,  
 
 PACS number: 72.80.Sk 
                                                          
* drshelke@gmail.com 
 
 
1. INTRODUCTION 
 
Doped perovskite manganites, exhibiting colossal 
magnetoresistance (CMR) effect have attracted consid-
erable attention not only for fundamental research, but 
also for potential applications [1, 2]. The magnetic 
property of ultrafine granular systems is an interesting 
subject of research for both theoreticians and experi-
mentalists. Considerable difference in magnetization 
has been observed by varying particle size and have 
attributed to the presence of nonmagnetic or magneti-
cally dead surface layer [3] or disordered spin orienta-
tion in the surface. The nature of interplay between the 
crystal structure, magnetic and transport properties of 
manganites is still a matter of discussion in spite of 
numerous investigations. The size and shape of parti-
cle, particle size distribution, and finite size effect and 
dipolar or exchange interaction between the particles 
strongly influence the properties of manganites [3, 4]. 
The underlying physical mechanism is that interac-
tions, one ferromagnetic (FM) and the other antiferro-
magnetic (AFM), shows variety of physical properties 
in magnetic (FM or AFM), charge (metal, insulator, or 
charge ordering), and orbital / lattice degrees of free-
dom [6]. The phenomenon of metal-insulator transition 
and electronic phase diagram in doped manganese ox-
ides with perovskite structure has not been satisfactori-
ly explained despite extensive efforts [2]. Most of the in-
vestigations show that the ferromagnetic Curie tempera-
ture and the metal-insulator transition temperatures in 
such materials are strongly dependent on composition and 
synthesis condition. A measurable effect, i.e. field induced 
modulation of resistance, has also been reported in the 
CMR manganites [7]. This makes the CMR oxides a likely 
candidate for use as semiconductors in novel field effect 
transistors with ferroelectric gate. These devices can be 
interrogated by reading the resistance (or conductance) of 
the CMR-based channel. Among all the compositions of 
La1 – xSrxMnO3, the La0.7Sr0.3MnO3 shows a variety of 
structural, electrical and magnetic transitions over a 
range of temperatures [8]. 
The physical properties of these materials are usually 
dependent on their preparation routes [9]. One of the most 
important aspects is the formation of high quality ceram-
ics and monophasic homogeneous thin films onto the suit-
able substrates for real applications. For applications a 
ceramic material consisting of small manganite particles, 
show a large grain boundary effect at low temperatures 
could also be interesting. It is therefore important to study 
the structure and physical properties of the CMR material 
at nanoscale. The samples with smaller grain sizes possi-
bly show richer electronic and magnetic properties, due to 
the influence of the structural and magnetic disorders at 
the grain interfaces. There have been several methods to 
prepare these manganites by varying micro to nanoparti-
cle size. We choose to prefer solid state reaction (SSR) and 
sol-gel (SG) technique due to the reason that in SSR, less 
expensive oxide precursors are used and the procedure is 
economical where as in SG method, low temperature, 
quality of precursors, homogeneity of precursors, and par-
ticle size can be controlled properly. In addition, a maxi-
mum possibility for quality formation of samples can be 
achieved in these techniques. 
In this report, an attempt has been made to sys-
tematically investigate the effect of different synthesis 
techniques on the structural and transport properties 
of LSMO bulk samples. We propose that metal-
insulator transition arises from particle size variation, 
is a universal feature of electron-correlated manganite 
nanoparticles. 
 
2. EXPERIMENTAL TECHNIQUE 
 
Powder samples of LSMO were prepared by tradi-
tional Solid state reaction (SSR) and sol-gel (SG) tech-
niques. In Solid state reaction method, the stoichio-
metric amounts of high purity chemicals La2O3, SrCO3 
and MnO2 were mixed in an agate mortar-pestle for 
several hours. In order to improve the reaction rate and 
ensure complete phase formation, intermediate grind-
ings were performed. The mix was calcined at 950 °C 
for 24. The well-calcined mass was pressed into pellets 
of 12 mm diameter and then sintered at 1100 °C for 
24 hours in an ambient air. 
 H.A. RESHI, V. SHELKE J. NANO- ELECTRON. PHYS. 5, 04053 (2013) 
 
 
04053-2 
During sol-gel process, (CH3COO)3La.XH2O, 
(CH3COO)2Sr.aq and (CH3COO)2Mn.4H2O were used 
as starting reagents. The precursors were dissolved in 
triple distilled water containing 30 ml acetic acid. The 
resulting transparent solution was thoroughly mixed 
with 100 ml ethylene glycol and then 20 % of ammoni-
um acetate solution was added. This complete solution 
was heated on a thermal plate under constant stirring 
at ~ 80 C to eliminate excess water. A homogeneous 
brown gel was achieved with heating at 110 C and 
finally brown-black powder was formed. The powder 
was ground for two hours and then calcined at 500 °C 
for 12 hours. The powder was pressed in the form of 
pellets and was sintered at 600 °C for 12 hours.   
The phase formation and crystal structure parame-
ters of the powder samples were identified by X-ray 
diffraction (D8 Advance Bruker) using CuKα radiation 
in the range 10≤ 2θ ≤ 60 with step size of 0.02°. Scan-
ning electron microscope (SEM) was used to obtain the 
grain structure and size. The electrical resistivity 
measurement was performed by standard four probe 
method using a commercial cryostat (Oxford Instru-
ments Inc., UK) in the temperature range 
10 K ≤ T ≤ 300 K. 
 
3. RESULT AND DISCUSSION 
 
3.1 Structural Analysis 
 
Figure 1 reveals the X-ray diffraction patterns for 
the samples with nominal composition LSMO sintered 
at 600 °C (SG) and 1100 °C (SSR) respectively. All the 
prominent peaks indicate the presence of parent com-
pound with orthorhombic (Pnma) and rhombohedral 
(R3C) lattice structure incase of SG and SSR sample. 
The grain size obtained through Scherer’s formula for 
nanocrystalline sample was 14 nm which is below the 
size obtained by SEM with a reasonable agreement.The  
 
 
 
Fig. 1 – X-Ray diffraction patterns for SG and SSR samples 
 
calculated values of lattice parameters along with 
synthesis conditions are shown in table 1. The XRD 
pattern of SG prepared sample indicates that the sam-
ple is fully crystallized without any kind of impurity. 
The synthesis of samples through SSR method needs 
higher temperature (1000-1600 °C) and long sintering 
time to obtain homogeneous composition and desired 
structures. High intensity of diffraction peaks for 
LSMO perovskite phase at high sintering temperature 
is the clear indication of better sample crystallinity. 
The SSR sample showed rhombohedral system which 
agree with early report [10, 11], however, we have ob-
served orthorhombic structure incase of SG sample. 
The rhombohedral-to-orthorhombic phase transition 
can be understood as a cooperative Jahn-Teller distor-
tion of MnO6 octahedra, one long and two short Mn-O 
bonds with reduced bond angle execute the orthorhom-
bic structure [12, 13] which is possible in nanosized 
LSMO compound.  
 
3.2 Microstructural Behaviour 
 
Figure 2 shows the polycrystalline samples synthe-
sized by SSR and SG techniques, depict the variable 
grain sizes observed through Scanning Electron  
Microscopy (SEM). There is a maximum variation in 
grain size as it is well known that grain size and grain 
connectivity varies with varying sintering and synthe-
sis techniques. The samples show spherical shape 
grains with average size of 2 m and 22 nm, a marginal 
variation observed in samples prepared through SSR 
and SG route. SG prepared samples consisted of ag-
glomerated nanoparticles organized by aggregation of 
smaller particles. Generally, the grain size increases as 
the sintering temperature is increased and at tempera-
ture above 1000 °C, rapid grain growth results in mi-
cron size particles. In general, the samples with large 
grain size showed linear electric behaviour while the 
small grain sized sample showed broader and wide 
metal-insulator transition. 
 
 
 
Fig. 2 – Scanning electron micrographs for a) SG and b) SSR 
samples 
 
3.3 Electrical Resistivity Measurement 
 
To assess the nature of resistivity, we measure the 
temperature dependent resistivity of LSMO samples 
 GRAIN SIZE INDUCED METAL-INSULATOR TRANSITION… J. NANO- ELECTRON. PHYS. 5, 04053 (2013) 
 
 
04053-3 
prepared by different synthesis techniques. Figure 3 
shows the temperature dependence of normalized zero 
field resistivity for LSMO SSR and SG samples. It is 
well known that electrical transport properties depend 
on grain size and the porosity of the pellets. The resis-
tivity value also appeared to be dependent to a large 
extent on the synthesis conditions. In order to perceive  
 
 
 
Fig. 3 – Temperature dependence of resistivity under zero 
fields for SG and SSR samples. 
 
the effect of grain size on the transport properties, our 
approach was to keep the sintering temperature in both 
the methods as low as possible. The sample prepared 
under SSR shows linear metallic behaviour throughout 
the measured range, however, the sample prepared by 
SG method shows a metal-insulator transition around 
250 K, indicates that the transition has a strong rela-
tion with reduced grain size, influenced by sintering 
and synthesis conditions. The resistivity of the sample 
increases with decrease in particle size changed by sys-
tematic sintering and synthesis method. A low tempe-
rature resistivity upturn appears in the SG sample, as 
a contribution of coulomb Blockade or Kondo effect  
[14, 15]. We argue that these features are predominant-
ly observed in nanomaterials with a possible existence 
of new interaction by strong correlation characteristics 
between the electrons in manganites. From the figure, 
it is observed that resistivity increases more than one 
order of magnitude as we move from SSR to SG. This 
increase in resistivity occurs due to enhanced scatter-
ing of the charge carriers by increasing the grain 
boundaries due to the smaller grain size as observed in 
SEM images. In SSR method, grain size increases leads 
to a decrease in grain boundaries and magnetic disor-
der. The resistivity for the samples with smaller crys-
tallite sizes shows the predominance of the grain 
boundary in the transport process. 
 
Table 1 – Synthesis conditions and the lattice parameters of 
La0.7Sr0.3MnO3 samples 
 
Sample 
Name 
Synthesis 
Technique 
Sintering 
Temperature 
a (Å) b (Å) c (Å) V (Å3) 
SSR 
Solid State 
Reaction 
1100 °C 
5.503 – 13.425 352.071 
SG Sol-Gel 600 °C 5.446 7.712 5.487 230.518 
 
4. CONCLUSION 
 
We synthesized the LSMO sample by solid state re-
action and sol-gel method and investigated their struc-
tural and transport properties. Both the samples have 
pure LSMO phase with orthorhombic and rhombohe-
dral unit cells. The sample prepared by SG method had 
nano range grain size and more disorder surface in 
comparison with SSR. The samples prepared with SG 
method restrict the grain growth due to low sintering 
and precursor temperature effects. The metal-insulator 
transition appears in finite sized sample is a character-
istic feature of strongly electron-correlated manganite 
system. 
 
ACKNOWLEDGEMENT 
 
We are thankful to University Grants Commission 
New Dehli and M. P. Council of science and technology, 
Bhopal for providing financial support. We are grateful 
to Dr. Rajiv Rawat and Dr. Mukul Gupta, UGC-DAE 
Consortium for Scientific Research, Indore for provid-
ing experimental facilities. 
 
 
REFERENCES 
 
1. E. Dagotto, Science 309, 257 (2005). 
2. Q.A. Pankhurst, J. Connolly, S.K. Jones, J. Dobson,  
J. Phys. D: Appl. Phys. 36, R167 (2003). 
3. M.B. Salamon, M. Jaime, Rev. Mod. Phys. 73, 583 (2001). 
4. S. Roy, I. Dubenko, D.D. Edorh, N. Ali, J. Appl. Phys. 96, 
1202 (2004). 
5. P.E. Jonsson, Adv. Chem. Phys. 128, 191 (2004). 
6. M. Suzuki, S.I. Fullem, I.S. Suzuki, L. Wang, C. Zhong, 
Phys. Rev. B 79, 024418 (2009). 
7. Y. Motome, N. Furukawa, Phys. Rev. B 71, 014446 (2005). 
8. P. Dey, T.K. Nath, U. Kumar, P.K. Mukhopadhyay,  
J. Appl. Phys. 98, 014306 (2005). 
9. M. Paraskevopoulos, F. Mayr, C. Hartinger, A. Pimenov, 
J. Hemberger, P. Lunkenheimer, A. Loidl, A.A. Mukhin, 
V.Y. Ivanov, A.M. Balbashov, J. Magn. Magn. Mater. 211, 
118 (2000). 
10. P. Dey, T.K. Nath, Phys. Rev. B 73, 214425 (2006). 
11. V. Shelke, A. Das, I. Dhiman, R. Yadav, S. Khatarkar, 
A. Anshul, R.K. Singh, J. Phys. Condens. Mater. 20, 
395218 (2008). 
12. K.P. Lim, S.W. Ng, S.A. Halim, S.K. Chen, J.K. Wong, Am. 
J. Appl. Sci. 6, 1153 (2009). 
13. J.F. Mitchell, D.N. Argyriou, C.D. Potter, D.G. Hinks, 
J.D. Jorgensen, S.D. Bader, Phys. Rev. B 54, 6172 (1996).  
14. O.L. Lebedev, J. Verbeeck, V. Tendeloo, C. Dubourdieu, 
M. Rosina, P. Chaudouet, J. Appl. Phys. 94, 7646 (2003). 
15. J. Zhang, Y. Xu, S. Cao, G. Cao, Y. Zhang, C. Jing, Phys. 
Rev. B 72, 054410 (2005). 
16. T. Sarkar, M.V. Kamalakar, A.K. Raychaudhuri, New J. 
Phys. 14, 033026 (2012). 
 


English

Grain Size Induced Metal-insulator Transition in La0.7Sr0.3MnO3 Compounds

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 4, 04053(3pp) (2013) Том 5 № 4, 04053(3cc) (2013)   2077-6772/2013/5(4)04053(3) 04053-1  2013 Sumy State University Grain Size Induced Metal-insulator Transition in La0.7Sr0.3MnO3 Compounds  Hilal Ahmad Reshi, Vilas Shelke*  Novel Materials Research Laboratory, Department of Physics, Barkatullah University, Bhopal (M.P.) India  (Received 23 August 2013; published online 31 January 2014)  The effect of different synthesis techniques on structural, microstructural and electrical properties of La0.7Sr0.3MnO3 (LSMO) was investigated. Two different techniques viz solid state reaction (SSR) and sol-gel (SG) method were used to prepare the samples. X-ray studies have confirmed the single phase for-mation of LSMO by both the techniques. The average grain size was 2 m for solid state reaction sample and 22 nm for sol-gel sample. A substantial enhancement in electrical resistivity was observed in the sam-ple with nanosized grains. The micro grain size sample exhibited metallic behaviour whereas nanoparticle sample showed metal-insulator transition around 250 K.  Keywords: Nanomaterials, Manganites, Metal-insulator transition,    PACS number: 72.80.Sk                                                           * drshelke@gmail.com   1. INTRODUCTION  Doped perovskite manganites, exhibiting colossal magnetoresistance (CMR) effect have attracted consid-erable attention not only for fundamental research, but also for potential applications [1, 2]. The magnetic property of ultrafine granular systems is an interesting subject of research for both theoreticians and experi-mentalists. Considerable difference in magnetization has been observed by varying particle size and have attributed to the presence of nonmagnetic or magneti-cally dead surface layer [3] or disordered spin orienta-tion in the surface. The nature of interplay between the crystal structure, magnetic and transport properties of manganites is still a matter of discussion in spite of numerous investigations. The size and shape of parti-cle, particle size distribution, and finite size effect and dipolar or exchange interaction between the particles strongly influence the properties of manganites [3, 4]. The underlying physical mechanism is that interac-tions, one ferromagnetic (FM) and the other antiferro-magnetic (AFM), shows variety of physical properties in magnetic (FM or AFM), charge (metal, insulator, or charge ordering), and orbital / lattice degrees of free-dom [6]. The phenomenon of metal-insulator transition and electronic phase diagram in doped manganese ox-ides with perovskite structure has not been satisfactori-ly explained despite extensive efforts [2]. Most of the in-vestigations show that the ferromagnetic Curie tempera-ture and the metal-insulator transition temperatures in such materials are strongly dependent on composition and synthesis condition. A measurable effect, i.e. field induced modulation of resistance, has also been reported in the CMR manganites [7]. This makes the CMR oxides a likely candidate for use as semiconductors in novel field effect transistors with ferroelectric gate. These devices can be interrogated by reading the resistance (or conductance) of the CMR-based channel. Among all the compositions of La1 – xSrxMnO3, the La0.7Sr0.3MnO3 shows a variety of structural, electrical and magnetic transitions over a range of temperatures [8]. The physical properties of these materials are usually dependent on their preparation routes [9]. One of the most important aspects is the formation of high quality ceram-ics and monophasic homogeneous thin films onto the suit-able substrates for real applications. For applications a ceramic material consisting of small manganite particles, show a large grain boundary effect at low temperatures could also be interesting. It is therefore important to study the structure and physical properties of the CMR material at nanoscale. The samples with smaller grain sizes possi-bly show richer electronic and magnetic properties, due to the influence of the structural and magnetic disorders at the grain interfaces. There have been several methods to prepare these manganites by varying micro to nanoparti-cle size. We choose to prefer solid state reaction (SSR) and sol-gel (SG) technique due to the reason that in SSR, less expensive oxide precursors are used and the procedure is economical where as in SG method, low temperature, quality of precursors, homogeneity of precursors, and par-ticle size can be controlled properly. In addition, a maxi-mum possibility for quality formation of samples can be achieved in these techniques. In this report, an attempt has been made to sys-tematically investigate the effect of different synthesis techniques on the structural and transport properties of LSMO bulk samples. We propose that metal-insulator transition arises from particle size variation, is a universal feature of electron-correlated manganite nanoparticles.  2. EXPERIMENTAL TECHNIQUE  Powder samples of LSMO were prepared by tradi-tional Solid state reaction (SSR) and sol-gel (SG) tech-niques. In Solid state reaction method, the stoichio-metric amounts of high purity chemicals La2O3, SrCO3 and MnO2 were mixed in an agate mortar-pestle for several hours. In order to improve the reaction rate and ensure complete phase formation, intermediate grind-ings were performed. The mix was calcined at 950 °C for 24. The well-calcined mass was pressed into pellets of 12 mm diameter and then sintered at 1100 °C for 24 hours in an ambient air.  H.A. RESHI, V. SHELKE J. NANO- ELECTRON. PHYS. 5, 04053 (2013)   04053-2 During sol-gel process, (CH3COO)3La.XH2O, (CH3COO)2Sr.aq and (CH3COO)2Mn.4H2O were used as starting reagents. The precursors were dissolved in triple distilled water containing 30 ml acetic acid. The resulting transparent solution was thoroughly mixed with 100 ml ethylene glycol and then 20 % of ammoni-um acetate solution was added. This complete solution was heated on a thermal plate under constant stirring at ~ 80 C to eliminate excess water. A homogeneous brown gel was achieved with heating at 110 C and finally brown-black powder was formed. The powder was ground for two hours and then calcined at 500 °C for 12 hours. The powder was pressed in the form of pellets and was sintered at 600 °C for 12 hours.   The phase formation and crystal structure parame-ters of the powder samples were identified by X-ray diffraction (D8 Advance Bruker) using CuKα radiation in the range 10≤ 2θ ≤ 60 with step size of 0.02°. Scan-ning electron microscope (SEM) was used to obtain the grain structure and size. The electrical resistivity measurement was performed by standard four probe method using a commercial cryostat (Oxford Instru-ments Inc., UK) in the temperature range 10 K ≤ T ≤ 300 K.  3. RESULT AND DISCUSSION  3.1 Structural Analysis  Figure 1 reveals the X-ray diffraction patterns for the samples with nominal composition LSMO sintered at 600 °C (SG) and 1100 °C (SSR) respectively. All the prominent peaks indicate the presence of parent com-pound with orthorhombic (Pnma) and rhombohedral (R3C) lattice structure incase of SG and SSR sample. The grain size obtained through Scherer’s formula for nanocrystalline sample was 14 nm which is below the size obtained by SEM with a reasonable agreement.The     Fig. 1 – X-Ray diffraction patterns for SG and SSR samples  calculated values of lattice parameters along with synthesis conditions are shown in table 1. The XRD pattern of SG prepared sample indicates that the sam-ple is fully crystallized without any kind of impurity. The synthesis of samples through SSR method needs higher temperature (1000-1600 °C) and long sintering time to obtain homogeneous composition and desired structures. High intensity of diffraction peaks for LSMO perovskite phase at high sintering temperature is the clear indication of better sample crystallinity. The SSR sample showed rhombohedral system which agree with early report [10, 11], however, we have ob-served orthorhombic structure incase of SG sample. The rhombohedral-to-orthorhombic phase transition can be understood as a cooperative Jahn-Teller distor-tion of MnO6 octahedra, one long and two short Mn-O bonds with reduced bond angle execute the orthorhom-bic structure [12, 13] which is possible in nanosized LSMO compound.   3.2 Microstructural Behaviour  Figure 2 shows the polycrystalline samples synthe-sized by SSR and SG techniques, depict the variable grain sizes observed through Scanning Electron  Microscopy (SEM). There is a maximum variation in grain size as it is well known that grain size and grain connectivity varies with varying sintering and synthe-sis techniques. The samples show spherical shape grains with average size of 2 m and 22 nm, a marginal variation observed in samples prepared through SSR and SG route. SG prepared samples consisted of ag-glomerated nanoparticles organized by aggregation of smaller particles. Generally, the grain size increases as the sintering temperature is increased and at tempera-ture above 1000 °C, rapid grain growth results in mi-cron size particles. In general, the samples with large grain size showed linear electric behaviour while the small grain sized sample showed broader and wide metal-insulator transition.    Fig. 2 – Scanning electron micrographs for a) SG and b) SSR samples  3.3 Electrical Resistivity Measurement  To assess the nature of resistivity, we measure the temperature dependent resistivity of LSMO samples  GRAIN SIZE INDUCED METAL-INSULATOR TRANSITION… J. NANO- ELECTRON. PHYS. 5, 04053 (2013)   04053-3 prepared by different synthesis techniques. Figure 3 shows the temperature dependence of normalized zero field resistivity for LSMO SSR and SG samples. It is well known that electrical transport properties depend on grain size and the porosity of the pellets. The resis-tivity value also appeared to be dependent to a large extent on the synthesis conditions. In order to perceive     Fig. 3 – Temperature dependence of resistivity under zero fields for SG and SSR samples.  the effect of grain size on the transport properties, our approach was to keep the sintering temperature in both the methods as low as possible. The sample prepared under SSR shows linear metallic behaviour throughout the measured range, however, the sample prepared by SG method shows a metal-insulator transition around 250 K, indicates that the transition has a strong rela-tion with reduced grain size, influenced by sintering and synthesis conditions. The resistivity of the sample increases with decrease in particle size changed by sys-tematic sintering and synthesis method. A low tempe-rature resistivity upturn appears in the SG sample, as a contribution of coulomb Blockade or Kondo effect  [14, 15]. We argue that these features are predominant-ly observed in nanomaterials with a possible existence of new interaction by strong correlation characteristics between the electrons in manganites. From the figure, it is observed that resistivity increases more than one order of magnitude as we move from SSR to SG. This increase in resistivity occurs due to enhanced scatter-ing of the charge carriers by increasing the grain boundaries due to the smaller grain size as observed in SEM images. In SSR method, grain size increases leads to a decrease in grain boundaries and magnetic disor-der. The resistivity for the samples with smaller crys-tallite sizes shows the predominance of the grain boundary in the transport process.  Table 1 – Synthesis conditions and the lattice parameters of La0.7Sr0.3MnO3 samples  Sample Name Synthesis Technique Sintering Temperature a (Å) b (Å) c (Å) V (Å3) SSR Solid State Reaction 1100 °C 5.503 – 13.425 352.071 SG Sol-Gel 600 °C 5.446 7.712 5.487 230.518  4. CONCLUSION  We synthesized the LSMO sample by solid state re-action and sol-gel method and investigated their struc-tural and transport properties. Both the samples have pure LSMO phase with orthorhombic and rhombohe-dral unit cells. The sample prepared by SG method had nano range grain size and more disorder surface in comparison with SSR. The samples prepared with SG method restrict the grain growth due to low sintering and precursor temperature effects. The metal-insulator transition appears in finite sized sample is a character-istic feature of strongly electron-correlated manganite system.  ACKNOWLEDGEMENT  We are thankful to University Grants Commission New Dehli and M. P. Council of science and technology, Bhopal for providing financial support. We are grateful to Dr. Rajiv Rawat and Dr. Mukul Gupta, UGC-DAE Consortium for Scientific Research, Indore for provid-ing experimental facilities.   REFERENCES  1. E. Dagotto, Science 309, 257 (2005). 2. Q.A. Pankhurst, J. Connolly, S.K. Jones, J. Dobson,  J. Phys. D: Appl. Phys. 36, R167 (2003). 3. M.B. Salamon, M. Jaime, Rev. Mod. Phys. 73, 583 (2001). 4. S. Roy, I. Dubenko, D.D. Edorh, N. Ali, J. Appl. Phys. 96, 1202 (2004). 5. P.E. Jonsson, Adv. Chem. Phys. 128, 191 (2004). 6. M. Suzuki, S.I. Fullem, I.S. Suzuki, L. Wang, C. Zhong, Phys. Rev. B 79, 024418 (2009). 7. Y. Motome, N. Furukawa, Phys. Rev. B 71, 014446 (2005). 8. P. Dey, T.K. Nath, U. Kumar, P.K. Mukhopadhyay,  J. Appl. Phys. 98, 014306 (2005). 9. M. Paraskevopoulos, F. Mayr, C. Hartinger, A. Pimenov, J. Hemberger, P. Lunkenheimer, A. Loidl, A.A. Mukhin, V.Y. Ivanov, A.M. Balbashov, J. Magn. Magn. Mater. 211, 118 (2000). 10. P. Dey, T.K. Nath, Phys. Rev. B 73, 214425 (2006). 11. V. Shelke, A. Das, I. Dhiman, R. Yadav, S. Khatarkar, A. Anshul, R.K. Singh, J. Phys. Condens. Mater. 20, 395218 (2008). 12. K.P. Lim, S.W. Ng, S.A. Halim, S.K. Chen, J.K. Wong, Am. J. Appl. Sci. 6, 1153 (2009). 13. J.F. Mitchell, D.N. Argyriou, C.D. Potter, D.G. Hinks, J.D. Jorgensen, S.D. Bader, Phys. Rev. B 54, 6172 (1996).  14. O.L. Lebedev, J. Verbeeck, V. Tendeloo, C. Dubourdieu, M. Rosina, P. Chaudouet, J. Appl. Phys. 94, 7646 (2003). 15. J. Zhang, Y. Xu, S. Cao, G. Cao, Y. Zhang, C. Jing, Phys. Rev. B 72, 054410 (2005). 16. T. Sarkar, M.V. Kamalakar, A.K. Raychaudhuri, New J. Phys. 14, 033026 (2012).  

https://essuir.sumdu.edu.ua/bitstream/123456789/35542/1/B2F69d01.pdf

Grain Size Induced Metal-insulator Transition in La0.7Sr0.3MnO3 Compounds

Abstract

Similar works

Full text

Available Versions

SocioEconomic Challenges Journal (Sumy State University)

Electronic Sumy State University Institutional Repository