Infrared emission properties of RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn co-doped Co0.6Zn0.4Fe2O4 ferrites

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Abstract

The RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn ions co-doped Co–Zn ferrites were prepared by solid-state reaction method. X-ray diffraction, infrared spectra, X-ray photoelectron spectroscopy, Mössbauer spectroscopy and infrared emission measurement (IRE-2) were employed to investigate the effect of the substitution RE3+ and Mn ions for Fe3+ ones on the spinel structure, the chemical homogeneity, and the infrared emission properties of the Co–Zn ferrites. The substitution leads to non-monotonous change of the lattice parameters and infrared emissivity properties, which is mainly attributed to the partial cation exchange among the spinel structure of Co–Zn ferrites. The infrared emission properties of Co–Zn ferrites seem to be greatly influenced by the co-doped of RE3+ and Mn ions—maxima values were 0.96–0.97, found for LaF, NdF and GdF, respectively.

Introduction

Infrared radiant materials are widely used in various fields, such as infrared heating and infrared health, which possess excellent corrosion resistance, chemical stability, high abrasion resistance and easy workability [1], [2]. However, there are some disadvantages for this class of material for the application in military field. For example, how to further enhance their infrared emission properties in the particular wavebands still remains a challenging. The conventional silicate minerals cannot meet the requirements with an optional infrared emission property [3], [4], [5]. In order to solve the problems, selecting proper metal ions and/or rare earth ions, such as Mn, Ni, and Nd ions as additives, to doping ferrites may be an efficient way to improve their infrared emission properties in the particular wavebands. Study found that it can effectively enhance the infrared emission properties of spinel ferrites doped with transition metal or rare earth ions. This effect is quite prominent in the transition metal and rare earth ions co-doped spinel ferrites [6], [7].

The attractive infrared emission properties of spinel ferrites are essential due to its local structure. The general formula of spinel ferrite is denoted as AB2O4 [8], [9], where tetrahedral (A) sites and octahedral (B) sites are mainly located by divalent and trivalent cations [10], [11]. In spinel structure, cations preferentially occupy A sites or B sites, which depend on the cation size and the preference energy of octahedral sites. In actual situation, a completely random cations distribution occurs in most of the cases and the distribution may be represented as (A1−xBx)tet[AxB2−x]octO4 [12], [13], where x is the fraction of the A-site occupied by B cations. The partial substitution of high spin transition metal ions-3d elements and the rare earth ions-the 4f elements series-for Fe3+ ions in ferrites exhibit a strong spin-orbital (3d–4f) coupling.

Currently, there are several classic preparation methods for Co–Zn ferrites, such as solid-state reaction, chimie douce route and micro emulsion-assisted precipitation route [14], [15]. However, considering the perspective of industrial production, solid-state reaction method is more practical than other methods. Although solid-state reaction method will require at high-temperature treatment to decompose precursors and improve crystallinity, which results in lots of defects; however, the method has been widely used to prepare a variety of micron-scaled spinel ferrite materials [16], [17]. Recently, we successfully prepared the Co–Zn ferrites and the RE/Ni substituted Co–Zn ferrites (RE = Sm, Eu and Gd) by the solid-state reaction method. The particle size of the obtained Co–Zn ferrites is around 2 μm [7]. We propose to extend this work to other transition metal ions and rare earth ions co-doped Co–Zn ferrites, such as RE3+ and Mn4+ ions. On the one hand, and we tend to increase the types of the RE3+ ion, with a special emphasize on the lanthanide contraction effect on the infrared emission properties; on the other hand, to the best of our knowledge, there is no systematic and comprehensive report as to how RE/Mn co-doping influences the infrared emission properties of Co–Zn ferrites, particularly in the 8–14 μm spectral wavelength ranges. Therefore, the aim of this study is to incorporate RE3+ and Mn4+ into Co–Zn ferrites and optimize their co-doped effect on infrared emission properties in the 8–14 μm spectral wavelength ranges.

Section snippets

Experimental

The Co0.6Zn0.4(RE/Mn)0.8Fe1.2O4 (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) ferrites were synthesized by solid-state reaction method. The RE3+ and Mn ions co-doped ferrites (RE/Mn mol ratio are 0.00 and 0.02) were defined to UF and ReF, respectively. Starting materials were RE2O3, MnO2, Co2O3, ZnO and Fe2O3. These were mixed in required proportions in agate mortar and the powder mixture was pressed into pellets of 60 mm diameter under a uni-axial pressure of 30 MPa. The samples were sintered by

Phase analysis

The XRD patters of the samples under investigation are shown in Fig. 1. They are indexed in the spinel-like structure with no evidence of foreign phases. The lattice parameters (a) of ReF are listed in Table 1, which show an appreciable increase compared to that of UF. The change of lattice parameter has something to do with the larger radius of RE3+ ion, but the change is different from others reported [19], [20]. This result indicates the co-introduction of RE3+ and Mn ions compared to that

Conclusions

In conclusion, we prepared and characterized the IR emission properties of RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn co-doped Co–Zn ferrites. Studies show that the IR emission properties of the Co–Zn ferrites are very sensitive to the cation distribution in the A- and B-site, and have nothing to do with the lanthanide contraction. Another interesting phenomenon is that the IR emissivity of RE and Mn co-doped ferrites are higher than those of single RE or Mn ion doped Co–Zn ferrites.

Acknowledgements

This research was supported by Suzhou University Postdoctoral Fund 32317031 and Key Project in Science and Technology Innovation Cultivation Program of Soochow University (14109905).

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