Spectrochimica Acta Part A 74 (2009) 1050–1059 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Synthesis of (Ca,Nd)TiO 3 powders by complex polymerization, Rietveld refinement and optical properties V.S. Marques a , L.S. Cavalcante b,∗ , J.C. Sczancoski b , E.C. Paris b , J.M.C. Teixeira a , J.A. Varela c , F.S. De Vicente d , M.R. Joya b , P.S. Pizani b , M. Siu Li d , M.R.M.C. Santos a , E. Longo c a CCN-Química, Universidade Federal do Piauí, 64049-550, Teresina, PI, Brazil b Departamento de Química/Física-UFSCar, P.O. Box 676, 13565-905, São Paulo, Brazil c Instituto de Química-UNESP, P.O. Box 355, 14801-907, Araraquara, SP, Brazil d Instituto de Física de São Carlos, USP, P.O. Box 369, 13560-970, São Carlos, SP, Brazil article info Article history: Received 19 February 2009 Received in revised form 25 August 2009 Accepted 26 August 2009 Keywords: (Ca0.99Nd0.01)TiO3 Rietveld refinement f–f transitions Photoluminescence abstract Neodymium calcium titanate, (Ca 0.99 Nd 0.01 )TiO 3 powders were synthesized by the complex polymeriza- tion method and heat treated at different temperatures for 2 h under air atmosphere. The structural evolution of these powders as a function of heat treatment temperature was analyzed by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. The optical properties were investigated by Ultraviolet–visible (UV–vis) absorption spectroscopy and Photoluminescence (PL) measurements. XRD patterns, Rietveld refinement and MR spectra indicated that the powders heated treated at 750 ◦ C for 2 h present an orthorhombic structure without secondary phases. UV–vis measurements suggested the presence of intermediary energy in disordered (Ca 0.99 Nd 0.01 )TiO 3 powders. Broad and narrow bands were observed in the PL spectra of these powders when excited with 350 nm wavelength. The broad bands were associated to the structural defects and/or p–d electronic transitions while, the narrow bands were ascribed to f–f transitions arising from Nd 3+ ions. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In the last years, several studies have been reported in the litera- ture on the structural phase transitions of calcium titanate (CaTiO 3 ) as a function of temperature and pressure [1–5]. In particular, this perovskite has a wide potential for applications in resonators and filters due to its high-dielectric constant and low-dielectric loss at high frequencies [6–14]. When doped with rare earth trivalent ions (La 3+ , Sm 3+ or Nd 3+ ), the dielectric properties of CaTiO 3 can be modified as consequence of the formation of Ca 2+ vacancies into the lattice [13,14]. On the other hand, this material is considered an incipient ferroelectric or quantum paraelectric at low tempera- tures. In this case, small perturbations (electric fields, elastic strains and impurities) can destroy the structural stability and induce a ferroelectric phase [15]. Lemanov et al. [16] reported a phase tran- sition from incipient to normal ferroelectric state in Ca 1-x Pb x TiO 3 solid solutions with Pb content up to x = 0.3. Currently, this perovskite has been employed for different technological purposes. For example, the formation of a CaTiO 3 interface layer on the hydroxyapatite-coated Ti substrates is able to increase the bond strength of this system as well as decrease the ∗ Corresponding author. Tel.: +55 16 3361 5215; fax: +55 16 3351 8214. E-mail address: laeciosc@bol.com.br (L.S. Cavalcante). progression of hydroxyapatite dissolution in acidic environment, which is produced by osteoclastic resorption in the human body [17–19]. Also, CaTiO 3 phase has contributed to the fast precipita- tion and deposition of silicon-substituted hydroxyapatite coatings on titanium substrates through the biomimetic method [17]. In the electrochemical area, Wang et al. [20] reported that CaTiO 3 - coated Ti electrodes modified with a thin hydrophobic layer are more corrosion resistance than the TiO 2 -coated Ti electrodes. In addition, Zr 4+ -doped CaTiO 3 powders (from 5 mol% to 7 mol%) [21] and CoO/CaTiO 3 catalysts [22] present a high efficiency in the water conversion process into hydrogen. In terms of photoluminescence properties, the CaTiO 3 has been mainly investigated when doped with Pr 3+ , Eu 3+ and Sm 3+ ions [23–32]. The use of these rare earth lanthanides into the matrix of this ceramic material results in the formation of red phosphors, except for the Sm 3+ , which it has been employed as an optical probe in order to estimate the degree of structural order. However, the literature does not report studies on the optical properties of Nd 3+ -doped CaTiO 3 . Different synthesis methods have been employed for the for- mation of this perovskite, mainly including: solid-state reaction or mechanochemical [33–37], molten salts [38–40], self-propagating high temperature [41–43], topochemical microcrystal conver- sion [44] and ultrasonic mist combustion/pyrolysis processes [45]. However, these methods present some drawbacks, such as: formation of secondary phases, contamination by impuri- 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.08.049