Materials Chemistry and Physics 88 (2004) 404–409 Low-temperature synthesis of single-phase Co 7 Sb 2 O 12 M.S.L. Brito a , M.T. Escote b,∗ , C.O.P. Santos c , P.N. Lisboa-Filho d , E.R. Leite b , J.B.L. Oliveira a , L. Gama e , E. Longo b a Departamento de Qu´ ımica, Universidade Federal da Para´ ıba, Jo˜ ao Pessoa, PB, Brazil b Laborat´ orio Interdisciplinar de Eletroqu´ ımica e Cer ˆ amica, Departamento de Qu´ ımica, Universidade Federal de S˜ ao Carlos, S ˜ ao Carlos, SP, Brazil c Laborat´ orio Computacional de Cristalografia e An´ alises Cristalinas, Instituto de Qu´ ımica, Universidade Estadual Paulista, Araraquara, SP, Brazil d Laborat´ orio de Supercondutividade de Magnetismo, Departamento de F´ ısica, Universidade Federal de S˜ ao Carlos, S ˜ ao Carlos, SP, Brazil e Laboratorio de Cerˆ amica, Departamento de Engenharia de Materiais, Universidade Federal de Campina Grande, Campina Grande, PB, Brazil Received 14 April 2004; received in revised form 6 August 2004; accepted 18 August 2004 Abstract Polycrystalline Co 7 Sb 2 O 12 compounds have been synthesized by a chemical route, which is based on a modified polymeric precursor method. In order to study the physical properties of the samples, X-ray diffraction (XRD), thermal analyses (TG and DSC), infrared spectroscopy (IR), specific surface area (BET), and magnetization measurements were performed on these materials. Characterization through XRD revealed that the samples are single-phase after a heat-treatment at 1100 ◦ C for 2 h, while the X-ray patterns of the samples heat-treated at lower temperatures revealed the presence of additional Bragg reflections belonging to the Co 6 Sb 2 O 6 phase. These data were analyzed by means of Rietveld refinement and further analyze showed that Co 7 Sb 2 O 12 displays an inverse spinel crystalline structure. In this structure, the Co 2+ ions occupy the eight tetrahedral positions, and the sixteen octahedral positions are randomly occupied by the Sb 5+ and Co 2+ ions. IR studies disclosed two strong absorption bands, ν 1 and ν 2 , in the expected spectral range for a spinel-type binary oxide with space group Fd3m. Exploratory studies concerning the magnetic properties indicated that this sample presents a spin-glass transition at T f ∼ 64 K. © 2004 Elsevier B.V. All rights reserved. Keywords: Polymeric precursor method; Spinel structure; Rietveld refinement; Spin-glass behavior 1. Introduction Spinel (Sp) oxides exhibit a wide variety of physical prop- erties, which make them interesting materials both from the scientific point of view and for technological application [1]. They are known as pigments with high thermal and chemical ability, and present refractory, magnetic, and catalytic prop- erties [2,3]. In this class of materials, the M 7 Sb 2 O 7 (M = Ni, Co) compounds display interesting magnetic properties [4]. In fact, depending on the M ion this system can be considered as a candidate to magnetic storage devices. The Co 7 Sb 2 O 7 powders crystallize in the general chem- ical formula (A)[B 2 ]O 4 , in which A is a divalent metal and B a trivalent one [5]. The Sp properties are dependent on the ∗ Corresponding author. Tel.: +55 16 3361 5215; fax: +55 16 3361 5215. E-mail address: mescote@liec.ufscar.br (M.T. Escote). nature of the ions A and B, their charge and their distribution between tetrahedral and octahedral sites [6]. It is common to call this normal Sp structure when the cations A are in the tetrahedral sites and the cations B are in the octahedral ones. When all the A ions are placed in the octahedral sites and, correspondingly, half of the B ions are in the tetrahedral sites, we refer to it as a totally inverted Sp [1,5]. As these compounds are rather sensible to the synthesis conditions, they display a great cation disorder [6]. This disorder is char- acterized by the inversion parameter i, which is the fraction of tetrahedral sites occupied by trivalent cations. Thus, the inversion parameter is 0, 2/3, and 1 for normal, random, and spinel inverse structures, respectively [5]. The antimonates Zn 7 Sb 2 O 12 and Co 7 Sb 2 O 12 constitute the first examples of cubic spinel with pentavalent and diva- lent cations [7]. Several works report on the zinc antimonate compounds, mainly due to their applications in ceramic varis- 0254-0584/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2004.08.008