Structural and electrical properties of the ceramic manganite Pr 0.6 Sr 0.4 Mn 1-x Cu x O 3
R. Chihoub1,2*, A. Amira1, N.Mahamdioua1, E.Lekhel1
1LEND, Faculty of Science and Technology Jijel University, Jijel 18000, Algeria.
* rymchihoub@yahoo.fr
S. P. Altintas2, A. Varilci2, C. Terzioglu2
2Physics Department, Abbant Izzet Baysal University, Bolu 14280, Turkey.
Abstract— The ceramics that are the focus of this paper , have a Perovskite structure (ABO3),with the general chemical formula Pr0.6Sr0.4Mn1-xCuxO3 (x=0.05) .The compounds are prepared by solid state reaction. The X-ray diffraction data are analyzed and it has been found that all the compounds crystallize in the orthorhombic structure. The observations by SEM show that the grain size decreases by copper doping. The temperature of magneto-resistivity curves are registered from room temperature down to 50K under a magnetic field up to 5 Tesla and showed that the undoped sample present a metal- insulator transition (I-M) at a temperature TP ≈ 210,23 K.
Some physical parameters are extracted and their evolution with magnetic field are presented and discussed.
Keyworlds—Manganite; Ceramic; Doping; Resistivity.
I. INTRODUCTION
In recent years, there has been a lot of interest in manganite perovskite ceramics Re1-xAxMnO3 (where R is rare earth element, A divalent alkaline earth element). This kind of ceramic material has a wide variety of applications due to its ionic conduction, magnetic, Electric , thermal and mechanical properties [1–4].
The origin of CMR behavior is explained initially by double exchange (DE) and Jahn–Teller effect and is subsequently extended to include spontaneous electronic phase separation, but still remains controversial [5]. In these manganites, a cascade of magnetic, structural, metal–
insulator and charge-ordering phase transitions have been observed by change of doped level, temperature and applied magnetic field [6].
In the aim to understand the effect of Cu doping, we have elaboreted and caracterized ceramics samples of nominal composition Pr0.6Sr0.4Mn1-xCuxO3 (x=0 and 0.05). We will show, that only the undoped sample present a insulator-
metal transition, the doped sample has an insulating behavior throughout temperature range. And is revealed an increase in the values of resistivity of the compound when doping by Cu in Mn site. A strong magnetoresistance is obtained for Pr0.6Sr0.4MnO3compound (26.60%).
II. EXPERIMENTAL DETAIL
Polycrystalline samples Pr0.6Sr0.4Mn1-xCuxO3 (x= 0 and 0.05) are prepared by the solid state reaction method from dried high purity Pr2O3, SrCO3, CuO and MnO2 powders.
The starting materials are intimately mixed in a agate mortar to obtain a homogeneous mixture. These mixtures are calcined in air at 800C° for 20h, pressed into pellets (of about 2 to 2,5 mm of thickness) and sintered at1000C°/20h, 1080C°/20h and 1180C°/20h respectively. Finally obtained samples were annealed at 800C° for 10h.
Samples Pr0.6Sr0.4MnO3and Pr0.6Sr0.4Mn0.95Cu0.05O3 will be noted PSM and PSMC, respectively.
Room-temperature powder X-ray diffraction (XRD) measurements are carried out on a Siemens D8-advance diffractometer in the Bragg–Brentano geometry using CuKα
radiation. The microstructural study of the samples done on a JEOL JSM-6390 LV scanning electron microscope .The resistivity of the samples in 0 and 5 T magnetic field was measured by the standard four-probe method on a cryodine CTI-Cryogenics closed cycle cryostat.
Magnetoresistance (MR) refers to the relative change in the electrical resistivity by the application of an external magnetic field. It is given by :
Where 0 and H represent the resistivities under zero and magnetic field H, respectively.
III. RESULTS AND DISCUSSION A. structural aspect
Fig.1 shows the X-ray diffraction patterns of the elaborated samples. These patterns reveals that all samples are single phase when compared to previously published
100
%
0
0
H
MR
results. The XRD data are refined using Jana 2006 software [7]. and it is displayed that the structure of all samples is orthorhombic , space group Pnma (N°62). No trace of impurity phases were detected in the XRD data. The refined cell parameters are given in Table1. This result suggests that doping by Cu on the Mn site cause a slight decrease of the values of lattice parameters and volume in agreement with previously reported values[8,9].
Representative SEM micrographs for Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.95Cu0.05O3 are shown in Fig.2. The scanning electronic microscopy reveals that The surface morphology of all the compositions showed that the grain size decrease from about 2- 4 μm to about 1-2μm by copper doping.
Figure 1. The superposition of the observed (dots) and the calculated (line) patterns of of PSM and PSMC.
TABLE I. THE REFIND CELL PARAMETERS OF COMPOUNDSPSMAND
PSMC.
Figure 2. SEM image of PSM and PSMC
Samples PSM PSMC
a(Å) 5.4748(5) 5.4730(4)
b(Å) 5.4373(5) 5.4400(5)
c(Å) 7.6610(7) 7.6585(7)
V(Å3) 228.061(9) 226.4(7)
RP(%) 11.84 12.59
RWP(%) 16.85 16.80
Gof 1.13 1.14
PSM
PSMC results. The XRD data are refined using Jana 2006 software
[7]. and it is displayed that the structure of all samples is orthorhombic , space group Pnma (N°62). No trace of impurity phases were detected in the XRD data. The refined cell parameters are given in Table1. This result suggests that doping by Cu on the Mn site cause a slight decrease of the values of lattice parameters and volume in agreement with previously reported values[8,9].
Representative SEM micrographs for Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.95Cu0.05O3 are shown in Fig.2. The scanning electronic microscopy reveals that The surface morphology of all the compositions showed that the grain size decrease from about 2- 4 μm to about 1-2μm by copper doping.
Figure 1. The superposition of the observed (dots) and the calculated (line) patterns of of PSM and PSMC.
TABLE I. THE REFIND CELL PARAMETERS OF COMPOUNDSPSMAND
PSMC.
Figure 2. SEM image of PSM and PSMC
Samples PSM PSMC
a(Å) 5.4748(5) 5.4730(4)
b(Å) 5.4373(5) 5.4400(5)
c(Å) 7.6610(7) 7.6585(7)
V(Å3) 228.061(9) 226.4(7)
RP(%) 11.84 12.59
RWP(%) 16.85 16.80
Gof 1.13 1.14
PSM
PSMC results. The XRD data are refined using Jana 2006 software
[7]. and it is displayed that the structure of all samples is orthorhombic , space group Pnma (N°62). No trace of impurity phases were detected in the XRD data. The refined cell parameters are given in Table1. This result suggests that doping by Cu on the Mn site cause a slight decrease of the values of lattice parameters and volume in agreement with previously reported values[8,9].
Representative SEM micrographs for Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.95Cu0.05O3 are shown in Fig.2. The scanning electronic microscopy reveals that The surface morphology of all the compositions showed that the grain size decrease from about 2- 4 μm to about 1-2μm by copper doping.
Figure 1. The superposition of the observed (dots) and the calculated (line) patterns of of PSM and PSMC.
TABLE I. THE REFIND CELL PARAMETERS OF COMPOUNDSPSMAND
PSMC.
Figure 2. SEM image of PSM and PSMC
Samples PSM PSMC
a(Å) 5.4748(5) 5.4730(4)
b(Å) 5.4373(5) 5.4400(5)
c(Å) 7.6610(7) 7.6585(7)
V(Å3) 228.061(9) 226.4(7)
RP(%) 11.84 12.59
RWP(%) 16.85 16.80
Gof 1.13 1.14
PSM
PSMC
B. Electrical behavior and magntoresistance
The evolution of the resistivity with temperature under Zero and 5Tesla for samples PSM and PSMC is plotted in fig.3. It is clear that only the undoped sample has an insulator-metal transition at a temperature TP. The doping by Cu causes a great increase of resistivity and lowers the temperature of the insulator-metal transition (Tp). The transition from the metallic to insulating state disappears by this doping. Indeed, it is clear from the curves of resistivity that compound PSMC has an insulating behavior throughout temperature range.
A similar result was observed by Reddy et al. [10] in La0.67-xEuxCa0.33MnO3 (x=0.25), the disappearance of the transition I-M may be caused by the decrease in the probability of charge transferred due to the deformation of the octahedra MnO6. So , this disappearance can be explained also by an excess of copper at the site of Mn in La2+4x/3Sr1-4x/3Mn1-xCuxO3( x=0.02) according W.J. Li et al [11].
The application of magnetic field causes a reduction of the resistivity of all the samples .
The reduction of the resistivity by the application of magnetic field which makes the a ferromagnetic state on the same temperature range more ordered, then the scattering function on carriers weakens. Also, the magnetic field can restrain thermal fluctuation and cause paramagnetic(PM) – ferromagnetic (FM) transition to occur at higher temperature , the temperature of I-M transition shift to higher temperature[12].
The temperature dependence of magnetoresistance (MR) at 5 Tesla for all samples are shown in fig 4. The highest obtained MR values is about 26.60% and 26.57 % at 5T for the Pr0.6Sr0.4MnO3 and La0.6Sr0.4Mn0.95Cu0.05O3 samples, respectively.
Figure 3. Temperature dependance of resistivity under 0 and 5T of PSM and PSMC
Figure 4. MR%. vs. temperature plots of PSM and PSMC under 0 and 5T.
IV. CONCLUSION
In summary, we have reported the Mn site Cu-doping effect on structure, and transport properties in the Pr0.6Sr0.4Mn1- xCuxO3(0≤x≤5%) systems. All the samples are good single phases with perovskite orthorhombic structures (Pbnm space group). Measurements of resistivity as a function of temperature show that only the un-doped simple present a insulator-metal transition. This latter disappears by Copper dopin, which also causes an increase in the values of resistivity of the compound.
R
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