Synthesis Growth and Characterization of Mn Doped La_1.8Sr_0.20cuO₄

Manish Verma¹*, N. P. Lalla², D. M. Phase² and V. K. Ahire²

¹University of Lucknow, Department of Physics, Lucknow - 226 007, India. 

²Ugc-Dae Csr, Indore, University Campus, Khandwa Road, Indore - 452 017, India.

DOI : http://dx.doi.org/10.13005/msri/080113

ABSTRACT:

Polycrystalline samples of La1.8Sr0.20Cu1-yMnyO4 (0≤y≤0.15) were synthesized by solid state reaction method. The phase purity was confirmed by powder X-ray diffraction. The scanning electron microscopy was done on the La_1.8Sr_0.20Cu1-yMnyO4 (0≤y≤0.15) samples. The superconductivity and Transition temperature were studied by four probe resistivity temperature method. The transition temperatures were measured nearly 37 k and were unchanged on Mn doping at Cu site in La1.8Sr0.20CuO4.

KEYWORDS: Solid state reaction method; X-ray diffraction; Scanning electron microscopy; Microstructure; SEM; Transition temperature; LSCO; Resistivity.

Copy the following to cite this article: Verma M, Lalla N. P, Phase D. M, Ahire V. K. Synthesis Growth and Characterization of Mn Doped La1.8Sr0.20cuo4. Mat.Sci.Res.India;8(1)

Copy the following to cite this URL: Verma M, Lalla N. P, Phase D. M, Ahire V. K. Synthesis Growth and Characterization of Mn Doped La1.8Sr0.20cuo4. Mat.Sci.Res.India;8(1). Available from: http://www.materialsciencejournal.org/?p=2501

Introduction

The discovery of high Tc superconductor by Bednorz and Muller in 1986 led to extensive research work on lamellar copper oxide materials to explain the high Tc superconducting mechanism.^1-4 To study the high Tc superconductivity and other physical properties the doping of various elements at Cu site was done by various research groups.^5-10 In La_2-xSr_xCuO₄, various attempts have been made to substitute a great variety of transition /rare earth metals for copper in La_2-xSr_xCuO_4.^9-11 When the Cu-site is doped by the other atoms, the superconducting transition temperature generally decreases monotically with increasing impurity doping concentration, which is usually explained by the traditional magnetic pair-breaking theory and other theories.^12-15 Among the various ions chosen as substitutes for Cu ions, C.H.Lee et.al found that the Mn ion doping at Cu site in La_1.85Sr_.15CuO₄ leads to unchanged Transition temperature.^12,16,17 In this paper we attempt to study the effect of Mn impurity doping at Cu site in La_1.80Sr_.20CuO₄.

Material and Methods

The polycrystalline samples were prepared by means of a conventional solid state reaction method using high-purity powders of La₂O₃, SrCO₃, CuO, and MnO₂. The powders were mixed, pressed into pellets, were then reacted at 1100°C for 7 days with three intermediate grinding. The chemical formula for the final compounds is La_1.8Sr_0.20Cu_1-yMn_yO₄ with y=0, 0.06, 0.10, 0.15. Phase identification was done with the help of X-ray Diffraction (XRD) pattern recorded on powder Rikagu Diffractometer using Cuk_α radiation. 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). Resistivity as a function of temperature for all the samples was measured using a standard four-probe method. Resistivity measurement was done in the temperature range of 1.5-300 K with DC resistivity precision one part in 10⁶.

Results and Discussion

Each sample was carefully characterized by powder X-ray diffraction and confirmed to be single phase which can be indexed as having tetragonal symmetry (see fig .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. The unit cell lattice parameters of the polycrystalline samples obtained by fitting a number of typical X-ray diffraction peaks are summarized in Table 1 below

It can be seen that the lattice parameter a increases with increasing Mn doping, which means that Mn doping alters the in-plane Cu(Mn)–O bond length effectively. Similarly the lattice parameter b increases with increasing Mn doping. The SEM picture of the LSCO sample with irregular grain size ≤ 1 µm is shown in fig. 2. We observe the grains are randomly distributed and there is low intergrain porosity.

In the present paper Mn doping at Cu site in La_1.8Sr_0.20CuO₄, the Mn impurity influences the superconductivity locally. However the most important difference between the nonmagnetic impurities doping case (like Zn and Al) and magnetic impurity Mn doping case is that former one decreases the Tc value while the latter does not. In 2007 the behavior of the unchanged Tc onset was investigated by one more research group, who obtained in La1.85 4/3xSr0.15+4/3xCu1-xMnxO4 polycrystalline ceramics alike result [18]. In 2008, C.J.Zhang et.al confirmed that Mn doping in La1.85Sr0.15CuO4 does not lead to a rapid decrease in the superconducting transition temperature, unlike in the case of doping with other elements (such as Ni, Zn, Fe, etc.) [12, 19, 20].We found that superconducting transition temperature (Tc) of La1.8Sr0.20Cu1-yMnyO4 with y=0, 0.06, 0.10 samples was unchanged on doping Mn at Cu site (see fig.3). These results does not agree with the view that Mn impurity doping destroys superconductivity by decreasing the Tc. Studying the diûerence between the Mn doping case and other elements(Zn, Al etc.) doping cases should provide us with a new way of understanding the mechanism of superconductivity. In summary, the polycrystalline samples of La_1.8Sr_0.20Cu_1-yMn_yO₄ were successfully synthesized using solid state reaction method. The powder XRD shows that La_1.8Sr_0.20Cu_1-yMn_yO₄ was tetragonal type phase which is well suited for polycrystalline sample. The superconducting properties of Mn doped La_2-xSr_xCuO₄ are clearly different from those of other elemental doping cases (such as Zn, Ni, Al etc). These different effects need further study.

Table 1: The unit cell lattice parameters of LSCO

Click on image to enlarge

Figure 1: X-ray diffraction of LSCO i.e. La_1.8Sr_0.20Cu_1-yMn_yO₄ with y=0, 0.06, 0.10, 0.15

Click on image to enlarge

Figure 2: SEM of LSCO i.e. La_1.8Sr_0.20Cu_1-yMn_yO₄ with y=0.15

Click on image to enlarge

Figure 3: The temperature dependence of Resistivity of the LSCO i.e. La_1.8Sr_0.20Cu_1-yMn_yO₄ with y=0, 0.06, 0.10 samples

Click on image to enlarge

Acknowledgements

The authors express their thanks to Dr.J.S.Verma, Dr.B.Das for their technical supports and discussion in the La_1.8Sr_0.20Cu_1-yMn_yO₄ sample synthesis and characterization. This work was supported by UGC-DAE-CSR, Indore (India) and University of Lucknow (India).

References

---

This work is licensed under a Creative Commons Attribution 4.0 International License.