using solid state route. XRD confirms that the sample is in single phase with tetragonal structure. Detailed analysis of temperature dependent resistivity revealed ...
Crystal structure and electrical transport properties of single layered perovskite LaSrCoO4 Abdul Ahad, D.K. Shukla, F. Rahman, S. Majid, Tarachand, G.S. Okram, D.M. Phase
Abstract
Department of Physics, Aligarh Muslim University, Aligarh, 202002, India UGC DAE Consortium for Scientific Research, Indore 452001, India
We have synthesized polycrystalline LaSrCoO4 that is single layered perovskite with K2NiF4 type structure. X-ray diffraction (XRD) studies confirms the phase with tetragonal structure. The structural parameters are refined by the Reitveld technique using FULLPROF code. Electrical resistivity performed in the temperature range 140300K shows semiconducting behavior of the sample.
Introduction A2BO4 Ruddlesden-Popper Excess AO
A2B2O7 Pyrochlore
Oxidation Perovskite ABO3 Reduction
Results Rietveld Refinement
Synthesis
A2B2O5 Brownmillerite
Excess of BO2
Stoichiometric La2O3 + SrCO3 + Co3O4
S O L I D
Grinding in room temperature
S T A T E S Y N T H E S I S
Refined lattice parameters:
Calcined for 8 hours, At 1000oC
Room temperature
a=3.80558 Å c=12.50108 Å
Re-grinding
Phase : Tetragonal
Pelletized Repeat if phase not obtained
Sintered for 12 hours, At 11500C
Space group : I4/mmm
Room temperature XRD
Fig. 1. Reitveld refined room temperature X-ray diffraction pattern
LaSrCoO4
Temperature dependent Resistivity
AB2O5 Pseudobrookite
The Cobaltite system under study belongs structurally to Ruddlesden-Popper series (AO)(ABO3)n. For n=1, K2NiF4 type structures are known as single layered oxides. Strontium doped La2CoO4 is fascinating because of mixed valence state of Cobalt. Spin state degree of freedom of the Co3+ play an important role in structural and transport properties.
T=225K
Thermally Activated behavior
S T R U C T U R A L
Fig. 3. Left panel: Representation of the K2NiF4 type structure of LaSrCoO4. Right panel: Representation of the cations coordination
Variable Range Hopping
Thermally Activated Behaviour Characterization Techniques Used X-Ray Diffraction Reitveld Refinement Temperature dependent Resistivity
Conclusions We have successfully synthesized the polycrystalline LaSrCoO4 using solid state route. XRD confirms that the sample is in single phase with tetragonal structure. Detailed analysis of temperature dependent resistivity revealed that in the high temperature region above 225K it follows the thermally activated behavior. Below 225K,it has been found that resistivity follows Variable range hopping model.
Fig. 2. Temperature dependent electrical resistivity (140-300K)
Variable range hopping (VRH) Mott Proposed variable range hopping mechanism for conduction at low temperature in 3D system
Here the exponent of T is 1/d+1, where d represent the dimensionality of the system
Fig. 4. lnρ vs. T-1/4 . Straight line is linear fitting to the 3D VRH model.
T R A N S P O R T
Here Ea represent the activation energy
Activation Energy Ea = 211meV Fig. 5. Left panel: The plot of lnρ against 1/T. Right panel: linear fitting to the High temperature resistivity data( above 225K)
Acknowledgement The authors gratefully acknowledge to UGC DAE CSR, Indore to provide experimental facilities for this work.
