Synthesis and characterization of Dy(OH)3 and Dy2O3 nanorods and nanosheets

https://doi.org/10.1016/j.ceramint.2014.11.085Get rights and content

Abstract

We synthesized Dy(III) complexes with morphologies of nanorods and nanosheets by a hydrothermal method. Cubic phase Dy2O3 nanorods and nanosheets were obtained by high temperature post-thermal annealing of the corresponding complexes. The as-synthesized nanorods consisted of hexagonal phase Dy(OH)3 grown along the [0 0 1] direction. Their physicochemical properties were examined by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction crystallography, UV-visible-NIR absorption, differential scanning calorimetry/thermogravimetric analysis and X-ray photoelectron spectroscopy.

Introduction

A great deal of effort has been devoted to synthesis of high-k gate dielectric materials as an alternative to silicon oxide. Dysprosium (Dy) oxide is one potential candidate material that has been extensively studied [1], [2], [3]. Dy2O3-based memory devices have shown excellent resistive switching behaviors [1], [2]. Dy2O3 has also shown the potential for application to magnetic resonance imaging (MRI) contrast agents in high magnetic fields owing to its excellent relaxation and relaxometric properties [4], [5], [6], [7], [8]. Das et al. synthesized Tb(III)-doped Dy2O3 nanoparticles (~3 nm dia.) and demonstrated they were useful as a high field single-phase bimodal MRI contrast agent and for in vitro fluorescence imaging [5]. Kattel et al. showed extensive potential applications of Dy2O3 and Dy(OH)3 to MRI contrast agents [7], [8]. Dy2O3 has also been used as an ac and dc magnetometer calibration standard [9]. Furthermore, the photocatalytic properties of Dy(OH)3 nanorods have been demonstrated by Liu et al. [10]. New materials are very important for pursuing potential applications. Various synthesis methods have been employed, including hydrothermal, so-gel, co-precipitation and thermal decomposition methods [11], [12], [13], [14], [15], [16], [17], [18]. Wang and Li prepared Dy(OH)3 nanorods with widths of 40–60 nm and lengths of 0.5–1 μm by a hydrothermal (180 °C, 12 h) method using 10% KOH solution [11]. Hydrothermal temperature is an important factor for controlling morphology [12]. Salavati-Niasari and Davar synthesized Dy carbonates nanoparticles by a sonochemical method and obtained Dy2O3 nanoparticles through post-calcination [13]. They also prepared Dy(OH)3 nanotubes by sonication of a Dy complex with hydrazine. Xu et al. synthesized Dy(OH)3 nanotubes from Dy2O3 powder in water by a simple hydrothermal treatment at 160 °C for 48 h [14]. Xiao et al. dissolved Dy(acac)3 in benzyl alcohol heated to 200 °C, and then calcinated the obtained products at 500 °C to obtain hierarchical Dy2O3 nanosheet microspheres [15]. In this process, benzyl alcohol was found to be a key morphology controlling agent.

In the present study, we synthesized Dy complexes (e.g., Dy(OH)3) with two different morphologies, nanorods and nanosheets. Dy2O3 nanostructures were obtained by post thermal treatment of the complexes without significantly impacting the morphologies. To the best of our knowledge, this is the first report of Dy2O3 nanosheets to date. The present study provides new insights for the development of novel functional materials, including high-k dielectric and MRI contrast agent materials.

Section snippets

Experimental section

Dy complexes were synthesized by a hydrothermal method as described below. First, 20 mL of 0.1 M Dy(III) nitrate hydrate (Sigma-Aldrich, 99.9%) were mixed with 5 mL of deionized water (18.2 MΩ cm resistivity), after which 1.0 mL of ethylene diammine (or 0.5–2.0 mL of 32% ammonia solution) was added to obtain white precipitates. The solution was then placed in a Teflon-lined stainless autoclave and heated at 120 °C or 210 °C for 12 h. The finally obtained white precipitates were washed with deionized

Results and discussion

Fig. 1 shows the SEM images of as-prepared and 700 °C-annealed samples synthesized under various conditions. Two different morphologies of nanorods and nanosheets were typically obtained. Samples A and D were obtained with 1.0 mL ethylene diammine (at 120 °C) and 0.25 mL ammonia (210 °C), respectively. The nanorods of sample A were 30–50 nm wide and 0.4 μm–1 μm long. The nanorods of sample D were thicker and longer, with widths of 200–300 nm and lengths of 1μm–3 μm. Interestingly, the edges of sample D

Conclusion

Hexagonal phase Dy(OH)3 nanorods were synthesized by a hydrothermal method. Nanosheets of a Dy complex could be obtained by varying the experimental conditions. Highly crystalline cubic phase Dy2O3 nanorods and nanosheets were obtained by post-annealing of the corresponding samples at 700 °C. Nanosheet morphology of Dy2O3 was reported for the first time. Their fundamental properties were fully examined by SEM, XRD, DSC/TGA, TEM, HETEM, UV–vis-NIR absorption, FT-IR, Raman and XPS. Dy(OH)3 was

Acknowledgment

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (NRF- 2011–0018403, and NRF-2012R1A1A4A01005645).

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