Selective Synthesis of TbMn 2 O 5 Nanorods and TbMnO 3 Micron Crystals Jian-Tao Han, ² Yun-Hui Huang,* ,²,‡ Wei Huang, ² and John B. Goodenough ‡ Laboratory of AdVanced Materials, Fudan UniVersity, Shanghai 200433, China, and Texas Materials Institute, ETC 9.102, The UniVersity of Texas at Austin, Austin, Texas 78712 Received July 31, 2006; E-mail: huangyh@mail.utexas.edu Multiferroic materials, in which more than one of ferromagnetic, ferroelectric, and ferroelastic properties appear simultaneously, have received renewed interest in recent years because of potential applications in new devices based on the mutual controls of magnetic and electric fields. 1 Many efforts have been devoted to finding new multiferroic materials or to investigating multiferroic properties in known oxides, such as BiCrO 3 , 2 BiMnO 3 , 3 BiFeO 3 , 4 BiCoO 3 , 5 BiNiO 3 , 6 BiScO 3 , 7 and double perovskite Bi 2 MnNiO 6 . 8 Recently, multiferroic effects have been found in some rare earth manganates. Hur et al. reported a profound interplay between electrical polarization and the applied magnetic field in TbMn 2 O 5 . 9 Kimura et al. observed giant magnetocapacitance and magneto- electric effects in TbMnO 3 . 10 For most multiferroic perovskite oxides, a high-pressure tech- nique is required to get a single phase. Not only is the equipment for the synthesis complicated, but also the microstructure of the sample cannot be controlled well. As is well-known, the properties of the samples strongly depend on their morphologies, sizes, and defect densities. 11 Thus the synthesis method is important for the functional materials. Our previous work on BiFeO 3 nanospindles showed that a facile, mild, and easily controlled hydrothermal route is available to synthesize multiferroic materials with uniform microstructure. 12 In this Communication, we describe a one-pot selective synthesis of multiferroic TbMn 2 O 5 nanorods and TbMnO 3 micrometer crystals with a convenient hydrothermal route. All chemicals were purchased from Shanghai Chemical Reagents Company and used without further purification. For a typical synthesis of TbMn 2 O 5 nanorods, 1.4 mmol MnCl 2 ‚H 2 O, 0.6 mmol KMnO 4 , 1.0 mmol Tb(NO 3 ) 3 ‚6H 2 O and 0.5 mol NaOH were dissolved in distilled water. After stirring for half an hour, the homogeneous solution was transferred into an 80 mL Teflon-lined steel autoclave and heated at 250 °C for 72 h. TbMnO 3 micrometer crystals were obtained via the same procedure as TbMn 2 O 5 nanorods by just changing the molar ratio of reactants MnCl 2 ‚4H 2 O and KMnO 4 from 7:3 to 4:1. The crystallinity and purity of the products were examined by X-ray diffraction (XRD) measurements on a Bruker X-ray diffrac- tometer with Cu KR radiation. XRD patterns of freshly prepared TbMn 2 O 5 nanorods and TbMnO 3 crystals are shown in Figure 1. All diffraction peaks of TbMn 2 O 5 can be perfectly indexed by an orthorhombic phase with space group Pbam (No. 55). The lattice parameters, refined with the Rietveld program MAUD, 13 are a ) 7.3272(2), b ) 8.5223(1), and c ) 5.6776(2) Å (Figure S1). For TbMnO 3 , the peaks can be indexed to an orthorhombically distorted perovskite phase with space group Pbnm (No. 62). The lattice constants are: a ) 5.3011(2), b ) 5.8510(1), and c ) 7.4006(3) Å (Figure S2). X-ray photoelectron spectroscopy (XPS, PHI Quantera SXM) shows that both TbMn 2 O 5 and TbMnO 3 consist of Tb, Mn, and O elements. The Mn 2p 3/2 binding energy of 641.8 eV is a characteristic of Mn 3+ (Figures S4b). 14 The Mn 2p doublet of TbMn 2 O 5 shifts by 0.7 eV toward higher binding energy compared to the Mn 2p doublet of TbMnO 3 , which is evident for a mixed Mn 4+/3+ state in TbMn 2 O 5 . 15 The morphology and microstructure of the samples were investigated with scanning electron microscopy (SEM, SHIMDAZU SSX-550). As shown in Figure 2A, TbMn 2 O 5 particles exhibit a uniform, rodlike morphology with an average size of about 2 µm in length and 200 nm in diameter. We further examined the microstructure with transmission electron microscopy (TEM) and high-resolution TEM (FEI CM-200 at 160 kV). The inset of Figure 2A shows a low-magnification TEM image of a typical TbMn 2 O 5 nanorod. The selected area electron diffraction (SAED) pattern in the inset of Figure 2B, taken along the [010] zone axis from an ² Fudan University. ‡ The University of Texas at Austin. Figure 1. XRD patterns of (A) TbMn2O5 and (B) TbMnO3. Figure 2. (A) SEM image of TbMn2O5 nanorods; right inset shows the TEM image of a single TbMn2O5 nanorod; (B) HRTEM image of the same nanorod; right inset shows a SAED pattern of the same nanorod; (C) SEM image of TbMnO 3 crystals; (D) HRTEM image of a single TbMnO3 micron crystal; right inset shows a SAED pattern of the same crystal. Published on Web 10/25/2006 14454 9 J. AM. CHEM. SOC. 2006, 128, 14454-14455 10.1021/ja065520u CCC: $33.50 © 2006 American Chemical Society Downloaded by UNIV OF LJUBLJANA on June 30, 2009 Published on October 25, 2006 on http://pubs.acs.org | doi: 10.1021/ja065520u