Journal of Alloys and Compounds 485 (2009) 565–568 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom The family of Ln 2 TeO 6 compounds (Ln = Y, La, Sm and Gd): Characterization and synthesis by the Pechini sol–gel process Jaime Llanos a,b,∗ , Rodrigo Castillo a , Daniel Barrionuevo a , Darío Espinoza a , Sergio Conejeros a a Departamento de Química, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile b Departamento de Química, Universidad de Antofagasta, Casilla 170, Antofagasta, Chile article info Article history: Received 4 May 2009 Received in revised form 2 June 2009 Accepted 3 June 2009 Available online 11 June 2009 Keywords: Nanostructures Sol–gel synthesis X-ray diffraction Thermal analysis abstract Nanocrystalline Ln 2 TeO 6 (Ln = Y, La, Sm, Gd) have been prepared by a Pechini sol–gel process using lan- thanide nitrates and telluric acid as precursors. All samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman and Fourier transform infrared spectroscopy (FT-IR), as well as thermogravimetric analysis (TG). The AFM study reveals that the samples consist of particles with average crystal size ranging from 70 to 110nm. The results of X-ray diffraction indicate that Ln 2 TeO 6 (Ln = Y, La, Sm, Gd) crystallize isotypically with the orthorhombic La 2 TeO 6 in the space group P2 1 2 1 2 1 . The infrared and Raman spectra show that the TeO 6 groups are independent vibrating groups and the results obtained were discussed on the basis of the site symmetry analysis derivates from the structural data. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In contrast to the large number of tellurates and hydrogen tel- lurates of the alkali metals, tellurates of transition metals, as well as tellurates minerals, a very few rare-earth metals tellurates have been reported [1–5]. Tellurates exists in two form, metatellurate ion, TeO 4 2- and orthotellurate ion TeO 6 2- [6]. For the lanthanide tellurates, only the orthotellurates of formula Ln 2 TeO 6 are known so far. The first rare- earth orthotellurates were prepared by Direct reaction of rare-earth oxide and orthotelluric acid at high temperature. In 1987, Trömel et al. have reported the crystal structure, from single crystal data, of La 2 TeO 6 and Yb 2 TeO 6 and proved that both phases crystallize in the orthorhombic system with space group P2 1 2 1 2 1 (no. 19) [7]. In the last years Schleid and co-workers have described the synthesis and the crystal structure of Gd 2 TeO 6 and Y 2 TeO 6 . They crystallize isotypically with the orthorrombic La 2 TeO 6 -structure type [8,9]. All of the Ln 2 TeO 6 compounds were prepared by the solid-state reac- tion method. This kind of reactions requires high temperatures and lengthy heating process. The present paper, which belongs to the framework of our sys- tematic study on the synthesis and characterization of rare-earth orthotellurates and their uses as host lattice in inorganic phosphors, describes a Pechini-type sol–gel synthesis of the nanocrystalline ∗ Corresponding author at: Dpto. Química, University Católica del Norte, Casilla 1280, Antofagasta, Chile. Tel.: +56 55 355624; fax: +56 55 355632. E-mail address: jllanos@ucn.cl (J. Llanos). Ln 2 TeO 6 (Ln = Y, La, Sm, Gd) as well as their Raman and IR spectra. 2. Experimental 2.1. Synthesis The orthotellurates of formula Ln2TeO6 (Ln = Y, La, Sm, Gd) were prepared by the Pechini sol–gel method [10,11]. According to the stoichiometric formula, 4.36 × 10 -3 mol of Y2O3 (Aldrich, 99.99% pure), La2O3 (Aldrich, 99.99% pure), Sm2O3 (Aldrich, 99.99% pure) and Gd2O3 (Aldrich, 99.99+% pure) were dissolved in 30 ml of HNO3 (0.5 mol dm -3 ) under vigorous stirring. The pH of the solution was adjusted between 1 and 2. When the oxides were completed dissolved, they were mixed with a water–ethanol (v/v = 1:7) solution containing citric acid (Merck, A.R) as chelat- ing agent for the metal ions and 4.36 × 10 -3 mol of H6TeO6 (Aldrich, 97.5–102.5% pure). The molar ratio of telluric acid to citric acid was 1:2. Afterward, c.a. 1.25g de polyethylene glycol) (PEG, M.W. = 20,000, Fluka, A.R.) was added as a cross-linking agent. Transparent sols were obtained after stirring for 2 h. The sols were dried in a 374 K water bath. When the sols were completely dry, they were annealed at 673 K in a furnace. After annealing, the resulting powders were fired to 1073 K with a heating rate of 1 K/min and kept there for 2 h. Optical inspection of the products showed homogeneous powders of white color. 2.2. Characterization To check the phase’s purity, powder X-ray diffraction (PXD) patterns were collected with an Imaging Plate Guinier Camera HUBER G670 (Cu K1 radiation,  = 0.15406 nm). FT-IR spectra were measured with PerkinElmer Spectrum BX spec- trophotometer with the KBr pellet technique. Raman spectra were obtained with the Witec alpha 300 microscope equipped with Confocal Raman Spectroscopy using a HeNe laser ( = 633 nm). The accuracy of the peak position is typically 4 cm -1 . All measurements were carried out at room temperature. Thermogravimetric analyses were performed using a PerkinElmer, Pyris TGA-7 apparatus. The experiments were carried in an atmosphere of Ar, using sample masses of approximately 40–50 mg in platinum sample pans and heating at 10 K/min from room temperature to 1473 K. The 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.06.027