Published on the Materials Research Bulletin, 44 (2009) 918-924. 1 Synthesis of Cr-Doped CaTiSiO 5 pigments by spray drying T. Stoyanova Lyubenova 1 , F. Matteucci 2 , A.L. Costa 2 , M. Dondi 2 , M.Ocaña 3 , J. Carda 1 1 University Jaume I, Campus del Riu Sec, 12071 Castellon de la Plana, Spain 2 Institute of Science and Technology for Ceramics, ISTEC-CNR, Faenza, Italy 3 Institute of Materials Science (CSIC), Sevilla, Spian Abstract. Cr-doped CaTiSiO 5 were synthesized by spray drying of an aqueous solution of precursor salts plus further calcining the resulting powders. The samples were prepared by conventional ceramic method as well for comparison study as ceramic pigments. The evolution of the present crystalline phases with applied thermal treatments has been studied by X-Ray Powder Diffraction (XRPD) and thermal analysis (DTA/TG). The powder morphology and particle size distribution were analyzed by scanning electron microscopy (SEM) and laser diffraction. The color efficiency of pigments was evaluated by colorimetric analysis (CIE Lab system). Results showed clearly efficiency of the spray dried procedure compared with the solid state reaction process. The produced powders consisted spherical particles with brad size distribution (<3µm), developing typical brown color. UV-VIS-NIR spectroscopy reveals the existence of Cr(III) as a majority phase occupies basically octahedral sites substituting Ti(IV), which must be responsible for the brown color of this pigment. Furthermore, Cr(IV) ions were found in octahedral coordination substituting Ti(IV) and small amount of tetravalent chromium substitutes for tetrahedral Si(IV). Keywords: titanite, ceramic pigments, spray drying, color, crystallochemistry. 1. Introduction Titanite (CaTiSiO 5 ) is an orthosilicate accessory mineral in igneous and metamorphic rocks [1] and is topologically identical with well known Malayaite (CaSnSiO 5 )[2]. It has a good thermal stability and is recommended as excellent candidate for a host lattice of ceramic materials [3]. Since it is possible to incorporate a variety of elements into the crystal lattice [4], it has been used for immobilization of radioactive waste from nuclear power reactors [5], however as luminescent material [6]. Titanite structure is colorless, but become colored when the matrix is doped with transition metal cations, which act as chromophore agents as Cr(III). More in details, Cr -doped titanite possesses reddish brown shadows. Therefore, the local environment of the chromophore cation in the host matrix along with it oxidation state [7] and content [8] determine the optical properties of this pigment. However, the chromium is known as the most adaptable chromophore used in ceramic pigments due to its variety of oxidation states which produce various colors depending on the crystal field strength of a host matrix and synthesis procedure. The transitional ion Cr(III) prefers octahedral environment than a tetrahedral one [9]. The titanite crystal structure consists of corner-sharing TiO 6 octahedra, connected via isolated SiO 4 tetrahedra to form TiOSiO 4 framework where the calcium ions are situated inside this network within very irregular heptacoordination, CaO 7 [10]. This six-fold coordination with