Study of conduction behavior in Pr0.67Sr0.03Ag0.30MnO3 Masroor Ahmad Bhat, Anchit Modi, Devendra K. Pandey, and N. K. Gaur
Citation: AIP Conference Proceedings 1953, 050044 (2018); doi: 10.1063/1.5032699 View online: https://doi.org/10.1063/1.5032699 View Table of Contents: http://aip.scitation.org/toc/apc/1953/1 Published by the American Institute of Physics
Study of Conduction Behavior in Pr0.67Sr0.03Ag0.30MnO3 Masroor Ahmad Bhat*, Anchit Modi, Devendra K. Pandey and N. K. Gaur Department of Physics, Barkatullah University, Bhopal-462026, India * Email:
[email protected] Abstract. In this paper, we report the conduction mechanism in Pr0.67Sr0.03Ag0.30MnO3 system synthesized via conventional solid state reaction route. The structural information was carried by X – Ray diffraction using Rietveld refinement which confirms the secondary phase of the sample. The SEM image shows the formation of double phase composite because of limited reaction of silver with parent compound. The resistivity behavior indicates the semiconducting behavior. The electronic nature can be estimated by means of variable range hopping (VRH) and small polaron hopping (SPH) model showing that the enhancement of double exchange interaction suppress the band gap and boost the carrier delocalization of charge carriers.
INTRODUCTION During last few decades a remarkable progress has been made in manganites which play a vital role showing interesting properties such as colossal magneto-resistance effect (CMR), charge/orbital ordering, metal to insulator transition and useful for promising applications of current era such as magnetic sensors, spintronic devices, bolometric sensors etc. [1, 2]. The importance of these materials is that their electronic and magnetic properties can be changed by different divalent and mono-valent substitutions at rare earth site [3]. Depending upon the requirement, the fascinating electronic and magnetic properties of these CMR materials can be altered by the application of electric/magnetic field, dopants, pressure, oxygenation, temperature and radiation etc giving rise to striking phenomena [2]. There are lots of reports on divalent dopants been considered at very extent and attention has been made on mono-valent substituent. The extraordinary benefit of mono-valant doing can vary carrier concentration and gives natural ideas which are favorable from application point of view in sensor technology [4]. By considering the above ascertained facts, we have induced silver at Sr site and got appealing purpose never has been reported earlier. Here, we have investigated the electronic properties envisaged by using different theoretical models of Pr0.67Sr0.13Ag0.20MnO3. We have observed that silver stimulation results in notable semiconducting behavior and can give better innovations from application point of view in manganites.
EXPERIMENTAL The polycrystalline samples of Pr0.67Sr0.33-xAgxMnO3 were synthesized via solid state reaction route. The stoichiometric quantities of high purity chemicals (Aldrich with better than 99.9% purity) Pr6O11, SrCO3, AgO and MnO2 were taken by using a muffle furnace operating in air. The compounds were mixed in agate mortar pastel and grinded for 2 hours. The calcination was performed twice at 950 °C for 12 hours with intermediate grindings. After calcinations the samples were grinded for 1 hour and were palletized by applying hydraulic pressure of 10 tons. The pallets obtained were finally sintered at 1200 °C for 24 hours. We carried out X- ray powder diffraction for structural identification by using FULLPROF program. The JEOL JSM - 6700 was used to observe the microstructure of the compound. The resistivity were measured by using standard four probe method in the temperature range 5K ≤ T ≤ 300K having liquid He cryostat and superconducting magnet.
2nd International Conference on Condensed Matter and Applied Physics (ICC 2017) AIP Conf. Proc. 1953, 050044-1–050044-4; https://doi.org/10.1063/1.5032699 Published by AIP Publishing. 978-0-7354-1648-2/$30.00
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RESULTS & DISCUSSION The X-ray diffraction pattern of our sample by using Rietveld refinement is shown in Fig. 1. It is evident that the diffraction pattern is having some secondary phase. The diffraction peak can be indexed on orthorhombic structure with the pnma space group. The obtained lattice parameters of reported sample a = 5.4113Å, b = 7.8198 Å, c = 5.4982 Å respectively and the cell volume 232.65 Å3. The goodness of fit (χ2 ≈ 2.051) and the presence of impurities indicate the limited reaction of silver with parent compound. The SEM image is shown in the inset of Fig.1 depicts that the excess Ag separates as metal and gathers at the grain surface of the host material which shows a two phase composite system.
FIGURE 1. Reitveld fitted XRD pattern of Pr0.67Sr0.03Ag0.3MnO3 compound and inset show the Scanning electron microscope (SEM) micrograph.
The Resistivity behavior shows the semiconducting nature of our compound. This behavior might be due to the fact that the excess silver doping delocalizes the charge carriers, causing local ordering of the electron spins. In order to investigate further the semiconducting nature of the present compound, resistivity data were analyzed by using small polaron hopping (SPH) model and Mott variable rang hopping (VRH) model.
FIGURE 2. Temperature dependence of electrical resistivity of Pr0.67Sr0.03Ag0.3MnO3 compound.
The VRH model originally verified in the lightly doped semiconductors with impurities randomly distributed. The expression for Mott-VRH model [5] is given as;
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With
Where r0 is the residual resistivity, T * is the characteristic temperature N (EF) is the density of state near the Fermi level, KB is the Boltzmann constant and x is the localization length.
(a)
(b)
FIGURE 3. (a) The relation between Log (r) vs. (1/T)-1/4 and (b) The relation between Log (r/T) vs. 1000/T.
The most probable hopping distance Rh (T) and the hopping energy Wh (T) can be written [6] at a given temperature T, as
The In(r) versus (1/T)-1/4 plot in Fig. 3(a) shows the linear behavior and fitted data which are shown as solid line. Using the fitted values of T * obtained from the above equations, we have estimated the values of N (E F), Rh and Wh by taking the localization length (ξ =lattice parameter). We have fitted the temperature dependence of resistivity data with the small polaron hopping model [6, 7] is given as
where Ea is the activation energy and A is the per-exponential. The polaron activation energy can be estimated form slop of the resistivity curve as In (r) versus 1/T curve displayed in Fig.3(b). The fitting procedure yielded a temperature scale T* = 16.453 × 10 5 K (R2 = 0.9992; standard error = 0.04). The encountered value is the same order of magnitude that determined for other transition metal oxides. By taking ξ = c = 5.4982 Å the estimated density of state N(EF) is 3.300 x1020 eV-1 cm-3. Further the Rh = 17.64 Å at room temperature and Wh = 5.55 meV. The calculated activation energy by small poloran hopping model is E a = 37.26 meV. The resistivity values increases with decreasing the temperature due to the fact that the excess silver doping delocalizes the charge carriers, causing local ordering of the electron spins. Resistivity behavior fits well with the VRH model and SPH model for the measured temperatures range signifying that the conduction mechanism.
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ACKNOWLEDGMENTS The authors are thankful to University Grant Commission (UGC), New Delhi for providing the financial support. Authors are also grateful to Dr. Rajeev Rawat and Dr. Mukul Gupta of UGC-DAE CSR, Indore for providing us experimental facilities.
REFERENCE 1. 2. 3. 4. 5. 6. 7.
Bhat et al., J. Alloys Compd. 661 (2016) 216. Choithrani et al., J. Mag. Mag. Mater. 361 (2014) 19. Lakshmi et al., Solid. State Sci. 12 (2010) 1731. Bhat et al., J Mater. Sci: Mater. Electron. 15 (2015) 3235. Modi et al., J. Mater. Sci. Mater. Electron. 27 (2016) 8899. Modi et al., J. Alloys Compd. 644 (2015) 575. Bhattacharya et al., Appl. Phys. Lett. 82 (2003) 23.
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