Lead nitroprusside: A new precursor for the synthesis of the multiferroic Pb2Fe2O5, an anion-deficient perovskite

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Highlights

  • Pb[Fe(CN)5NO] was synthesized and characterized.

  • Pb[Fe(CN)5NO] belongs to orthorhombic crystal system, space group Pnma.

  • Pb2Fe2O5 was obtained by thermal decomposition of Pb[Fe(CN)5NO].

  • Pb2Fe2O5 is a weak ferromagnet due to spin canting.

  • Ordering temperature of Pb2Fe2O5 from the fit of a phenomenological model was 520 K.

Abstract

In order to investigate the formation of multiferroic oxide Pb2Fe2O5, the thermal decomposition of Pb[Fe(CN)5NO] has been studied. The complex precursor and the thermal decomposition products were characterized by IR and Raman spectroscopy, thermal analysis, powder X-ray diffraction (PXRD), scanning electron microscopy and magnetic measurements. The crystal structure of Pb[Fe(CN)5NO] was refined by Rietveld analysis. It crystallizes in the orthorhombic system, space group Pnma. The thermal decomposition in air produces highly pure Pb2Fe2O5 as final product. This oxide is an anion deficient perovskite with an incommensurate superstructure. The magnetic measurements confirm that Pb2Fe2O5 shows a weak ferromagnetic signal probably due to disorder in the perfect antiferromagnetic structure or spin canting. The estimated ordering temperature from the fit of a phenomenological model was 520 K. The SEM images reveal that the thermal decomposition of Pb[Fe(CN)5NO] produces Pb2Fe2O5 with small particle size.

Graphical abstract

Field cooling (FC) and zero field cooling (ZFC) magnetization curves at H = 10 and 1000 Oe for Pb2Fe2O5 obtained at 750 °C. Remnant magnetization after applying H = 1 T, FC procedure at 0.8 Oe. The fitted expression (see text) yield an ordering temperature To = 520 K.

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Introduction

Nitroprussides of the type A[Fe(CN)5NO]·nH2O (A = Ca, Sr, Ba) have been studied as precursors for the synthesis of perovskite type oxides AFeO3–δ [1], [2]. The thermal decomposition of heteronuclear complexes was demonstrated to be a promising method for the preparation of homogeneous mixed oxides at an atomic level at low temperatures compared with the conventional ceramic method [1], [2], [3], [4], [5], [6], [7]. The use of a precursor containing the appropriate A/B ratio enforces the formation of ABO3 perovskites with the appropriate stoichiometry, thus controlling and preventing any elements segregation generally observed in conventional methods (ceramic method) and allowing the synthesis of the desired mixed oxide at very low temperatures and with a high purity [7]. The mixed oxides obtained by this method of synthesis have relatively high surface area compared with ceramic method and could be used as catalysts in different chemical reactions [8]. On the other hand, if the ratio A/B is not appropriate like in the case of Pb2[Fe(CN)6]·4H2O, mixtures of compounds are obtained [9], [10].

Perovskite type oxides with general formula ABO3–δ (A = Pb(II), Bi(III)) are considered good candidates for multiferroic materials in which ferroelectricity and magnetism coexist. This phenomena were observed in oxides such as BiFeO3 [11], BiCrO3 [12], PbCrO3 [13] and PbMnO3 [14]. The stereochemical effect of the 6s2 lone pair and the covalent A–O bonds (A = Pb(II) and Bi(III)) are expected to stabilize distorted non-centrosymmetric structures generating permanent electric dipoles (ferroelectricity) [13], [14]. Taking these observations into account, the preparation and study of perovskite materials that have both, a cation containing lone-pair of electrons as well as a magnetic ion located at the A and/or B perovskite sites is a design strategy to obtain new multiferroic compounds. Pb2Fe2O5, a perovskite with an incommensurate superstructure, was obtained by different methods of synthesis including ceramic method [15] or sol-gel synthesis [16]. In Pb2Fe2O5 the co-existence of ferromagnetism and ferroelectricity has been reported [16], being in this way a good multiferroic material candidate.

In the present article we report the synthesis, structural and spectroscopic characterization of lead nitroprusside (Pb[Fe(CN)5NO]) used as precursor for the synthesis of high purity Pb2Fe2O5. The crystal structure of the complex was refined by means of Rietveld analysis using laboratory powder X-ray diffraction (PXRD). These measurements were complemented with thermogravimetric and differential thermal analysis, IR and Raman spectroscopy. The mixed oxide Pb2Fe2O5 was obtained by thermal decomposition of the complex at 750 °C in air and it was characterized with the techniques mentioned previously. The magnetic properties of Pb2Fe2O5 have also been investigated.

Section snippets

Synthesis

Lead nitroprusside (PbNP) was obtained by an indirect method previously reported by different groups [1], [2], [17], [18], [19], [20]. The first step corresponds to the preparation of Ag2[Fe(CN)5NO] which was obtained by mixing aqueous solutions of Na2[Fe(CN)5NO] and AgNO3 in stoichiometric quantities under continuous stirring during two hours. The pink precipitate was separated by filtration and stored in a dry box with silica gel. In the second step, a suspension of Ag2[Fe(CN)5NO] in water

Crystal structure refinement

The PXRD pattern of PbNP refined at RT is shown in Fig. 1. Final cell parameters, atomic positions and discrepancy factors are shown in Table 1. Fig. 2 shows the atomic packing within the unit cell and the coordination environment for Pb and Fe atoms. Anhydrous PbNP crystallizes in the orthorhombic crystal system, in the space group Pnma. In the crystal structure the iron atom is coordinated to five C atoms of CN ligands and to the N atom of the NO group. The resulting octahedron, [Fe(CN)5NO]2−

Conclusions

In this study, highly pure Pb2Fe2O5 was synthesized by thermal decomposition of Pb[Fe(CN)5NO] (PbNP). PbNP decomposes in one step by losing the CN and NO groups to produce Pb2Fe2O5 as final product.

The crystal structure of PbNP was refined from PXRD data using Rietveld analysis. This compound crystallizes in the orthorhombic system, space group Pnma and Z = 4. In this structure the Fe atoms are octahedrally coordinated to five CN ligands and a NO group and Pb(II) cations are penta-fold

Acknowledgments

R.E.C. thanks FONCYT for PICT2007 303, CONICET for PIP #11220090100995 and SECyT-UNC for the Project 162/12. D.M.G. and D.G.F. thank CONICET for a fellowship. D.M.G. and M.I.G. thank CIUNT for financial support, Project 26D-428. G.N. thanks FONCYT for PICT2007 819, CONICET for PIP #11220090100448 and SECTyP-UNCuyo.

References (26)

  • M.I. Gómez et al.

    J. Solid State Chem.

    (1999)
  • M.I. Gómez et al.

    J. Solid State Chem.

    (2001)
  • P.K. Gallagher

    Mater. Res. Bull.

    (1968)
  • M.C. Navarro et al.

    J. Solid State Chem.

    (2005)
  • Y. Itagaki et al.

    Sens. Actuators B

    (2007)
  • D.M. Gil et al.

    Polyhedron

    (2012)
  • M. Wang et al.

    Mater. Res. Bull.

    (2011)
  • J. Amalvy et al.

    J. Phys. Chem. Solids

    (1985)
  • M.M. Vergara et al.

    Spectrochim. Acta

    (1993)
  • C.O. Della Vedova et al.

    J. Mol. Struct.

    (1981)
  • E. Traversa et al.

    J. Mater. Res.

    (1998)
  • M.C. Navarro et al.

    J. Therm. Anal. Calorim.

    (2010)
  • D.M. Gil et al.

    J. Therm. Anal. Calorim.

    (2011)
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