Structural and Transport Properties of Nd0.6Sr0.4CoO3 Compound
Anchit Modi1*, Masroor Ahamd Bhat1, Devendra K. Pandey1, Tarachand3, Shovit Bhattacharya2, G. S. Okram3, N. K. Gaur1 1Department
of Physics, Barkatullah University, Bhopal 462026, India 2Technical Physics Division, Bhabha Atomic Research Center, Mumbai-400085, India 3UGC-DAE, Consortium for Scientific Research, University Campus, Khandwa Road, Indore-452001, India *Email-
[email protected]
Motivation The Rare-earth cobaltates of the general formula Ln1-xAxCoO3 (Ln = rare earth, A = alkaline earth), possessing the perovskite structure, demonstrate a wide range of different phenomena: spin-state transitions, metal–insulator transition, giant magnetoresistance various types of magnetic, orbital/charge ordering; and structural phase transitions. The spin-crossover transition in LaCoO3 identified several years ago, was first considered to transform from the low-spin (t62ge0g; S = 0) state to the highspin (t42ge2g; S = 2) state and the transition has been studied by various methods including Mossbauer spectroscopy. While LaCoO3 is rhombohedral, PrCoO3 and NdCoO3 are orthorhombic due to the greater distortion of the CoO6 octahedron and with the decrease in the size of the rare earth ion a behavior commonly found similar to other rare earth compounds such as the manganites.
Characterization
Synthesis
The electronics transport properties visualized by using small poloran model (SPH) in Nd0.6Sr0.4CoO3 compound. We have observed that Sr doping results in remarkable semiconducting behavior and exhibits larger thermopower near room temperature can be used for semiconducting and thermoelectric application.
Samples have been synthesized by conventional solid state reaction
Electrical Resistivity
technique.
Using the symbol of the temperature coefficient of resistivity, here, dρ/dT < 0 for both samples shows the semiconductor nature. The resistivity data have been fitted with the small polaron hopping model is given as
The stoichiometric amounts of high purity (≥ 99.99%) chemical of Nd2O3, SrCO3 and Co3O4 were mixed in an agate mortar pestle. The calcined powders were thoroughly grinded and compacted into circular pallets of 10 mm diameter with around 2-3 mm thickness.
Ea AT exp KT
The pallets were sintered at 12000C for 24 hours each with intermediate grindings to ensure the chemical reaction goes to completion and that the material product contains only the desired homogenous single phase.
Where Ea is the activation energy and A is the perexponential. The activation enrgy is 0.0123 eV for Nd0.6Sr0.4CoO3 and the correlation factor R= 0.99514 of sample.
Structural
X-ray Diffraction, Cu Ka radiation, 20 ≤ 2θ ≤ 100, Rietveld Analysis
Morphology
Scanning electron microscopy at room temperature
The responsible issue for increasing the resistivity at low temperature is that there is a decline in the carrier concentration along with the reduction of mobility that can be recognized due to breaking of the conduction path along Co-O arrangement and thus suppress the Co3+/Co4+ ratio.
Resistivity Thermopower
Four probe method, 5 K ≤ T ≤ 300K, liquid He cryostat
Thermo-electric power (S) measurements, 10 K ≤ T ≤ 300K, liquid He cryostat
Results and Discussion Reitveld fitted XRD
SEM Images
Thermopower
The seeback cofficient is positive remains for the whole temperature region of our measurements without any change in the sign, indicating the holes are the major charge carriers responsible for thermoelectric transport.
Conclusion
The XRD analysis shows that the both samples are homogenous and mono-phase in nature with no detectable secondary phase. The crystal structure of both compounds are orthorhombic with Pbnm space group.
The morphology of these samples are found to be quite uniform which suggest the good crystalline nature of these sample
Strctural, electrical and tharmal transport properties of the polycrystyalline Nd0.6Sr0.4CoO3 perovskites synthesized by solid state reaction method have been studied systematically. The structure study shows that the synthesized compound crystallizes in the orthorhombic structure with Pbnm space group. The temperature dependent resistivity study indicates the semiconductor behavior. The small poloran hopping conduction model described semiconducting phase fairly well and the calculated activation energy EP ≈ 0.0123eV with the best correlation factor R ≈ 0.99514. The seeback coefficient is positive in whole temperature range indicates the hole is the majority charge carrier in the reported system.
References Stauffer et al., Phys. Rev. B 70 (2004) 214414 Asai at al., Phys. Rev. B 86 (2012) 014421 Kumar et al., J. Appl. Phys. 113 (2013) 043918 Mahendiran et al., Appl. Phys. Lett. 101 (2012) 042411 Modi et al. J. Mater. Sci. Mater. Electron. 27 (2016) 8899–8905. Modi et al., J. Alloys Compd. 644 (2015) 575-581.
