Synthesis Growth and Characterization of La1.8m0.20cu1-Xmnxo4, (M=Sr,Ca) Oxides

Introduction

There is now extensive research work on lamellar copper oxide materials to explain the mechanism of various phenomenons in oxides [1-6]. To study the phenomenon like superconductivity, magnetoresistance & other physical properties the doping of various elements at Cu site was done by various research groups [5-7]. In this paper we attempt to explain the accurate condition.

Materials and Methods

The polycrystalline samples were prepared by means of a conventional solid state reaction method using high-purity powders of La₂O₃, SrCO₃/CaCO₃, CuO, and MnO₂. The powders were mixed, pressed into pellets, were then reacted at 1100ºC for 7 days with three intermediate grinding. The chemical formula for the final compounds is La_1.8M_0.20Cu_1-xMn_xO₄ with x=0, 0.10, 0.15, 0.20 & M=Sr/Ca. Phase identification was done with the help of X-ray Diffraction (XRD) pattern recorded on powder Rikagu Diffractometer using Cuk_α radiation. Rikagu Diffractometer has scanning rate of 2 degree per minute. Microstructure was analyzed by Scanning Electron Microscopy (SEM) JEOL JSM 5600. Also EDAX was done on these samples to map the elements present in samples (not shown). Resistance as a function of temperature for all the samples of LSCO was measured using a standard four-probe method. Magnetoresistance (MR) was measured as a function of Temperature.

Results and Discussion

Each sample of  La_1.8Sr_0.20Cu_1-xMn_xO₄ & La_1.8Ca_0.20Cu_1-xMn_xO₄ was carefully characterized by powder X-ray diffraction and confirmed to be single phase which can be indexed as having K₂NiF₄-type tetragonal symmetry (not shown) & Orthorhombic symmetry respectively (see figure 1). No impurity peaks are present in the X-ray Diffraction patterns. Mn definitely substitutes for Cu site as confirmed by the fact that the samples with Mn doping remain single phase.

Figure 1: X-ray diffraction of LCCO i.e. La1.8Ca0.20Cu1-xMnxO4with x=0,0.10, 0.15,0.20 Click here to View figure

Figure 2a:  LSCO, y=0 and Figure 2b: LSCO Click here to View figure

The SEM pictures of the LSCO samples with irregular grain size <1 µm are shown in fig. 2a, fig.2b. We observe the grains are randomly distributed and there is low intergrain porosity.   The SEM of LCCO (not shown).

 

Figure 3: The magnetoresistance (MR) of La1.8Ca 0.2Cu0.85Mn0.15O4. Click here to View figure

The figure 3 shows that the MR of  La_1.8Ca_0.2Cu_0.85Mn_0.15O₄ decreases with increasing temperature due to less scattering from Mn at constant magnetic field of 0,1,3,5 tesla. Thus LCCO is magnetoresistive oxide.

Figure 4: R-T plot for undoped LSCO. Click here to View figure

Figure 4 shows the temperature dependence of resistance of the La_1.8Sr_0.20CuO₄.For undoped LSCO the transition temperatures was measured to be 36.766k.

Conclusion

In summary, the polycrystalline samples of    La_1.8Sr_0.20Cu_1-xMn_xO₄  (LSCO) & La_1.8Ca_0.20Cu_1-xMn_xO₄ (LCCO) were synthesized using solid state reaction method. The powder XRD shows that La_1.8Sr_0.20Cu_1-xMn_xO₄ was tetragonal K₂NiF₄ type phase which is well suited for polycrystalline sample while La_1.8Ca_0.20Cu_1-xMn_xO₄ was orthorhombic symmetry. The La_1.8Ca _0.2Cu_0.85Mn_0.15O_4.

sample was found to be magnetoresistive while the La_1.8Sr_0.20CuO₄ sample was found to be superconducting. These different effects need further study.

Acknowledgements

The authors express their thanks to Dr.J.S.Verma, Dr.R.P.singh & Dr B.Das for their technical supports and discussion in the La_1.8Sr_0.20Cu_1-xMn_xO₄ & La_1.8Ca_0.20Cu_1-xMn_xO₄ samples synthesis and characterization. This work was supported by UGC-DAE-CSR, Indore (India) and University of Lucknow (India).

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