CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 39 (2013) 489–495 Porcelain containing anatase and rutile nanocrystals N. Bouzidi a,n , A. Bouzidi b , P. Gaudon c , D. Merabet a , P. Blanchart d a University of Bejaia, Materials Technology Laboratory of Process Engineering (LTMGP). Targua Ouzemmour Road, Bejaia 06000, Algeria b University of Bejaia, Electrical Engineering Laboratory (LGE), Targua Ouzemmour Road, Bejaia 06000, Algeria c Ecole des Mines d’Al  es, Centre des Mate´riaux de Grande Diffusion (CMGD). 6, Av. de Claviere, 30319 Ale´s, France d GEMH ENSCI, 12 Rue Atlantis, 87068 Limoges, France Received 25 May 2012; received in revised form 13 June 2012; accepted 18 June 2012 Available online 1 July 2012 Abstract The aim of this work is to study the dielectric of two porcelains containing TiO 2 in the form of anatase and rutile. TiO 2 was added in compositions by means of raw kaolin with a relative high quantity of anatase, or the addition of anatase powder (10 wt%) in the initial mixture. An alternative porcelain containing kaolin–anatase mixture was obtained by a preliminary firing at 1300 1C. Beside kaolin, compositions also contain quartz and alkaline feldspar. The microstructural observations show various crystalline phases and micropores, which also have an effective role in affecting the properties. The dielectric characterization of fired porcelain, in the frequency range of 10 5 –10 9 Hz, shows that permittivity value can be increased from 7.19 to 8.41, depending in TiO 2 crystal type, morphology and content. Permittivity depends also on mullite, quartz and cristobalite, quantities, but the role of TiO 2 phase is predominant. The macroscopic permittivity of porcelains can be calculated using a mixing rule, which fit accurately experimental results. & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: C. Dielectric properties; D. Porcelain; Rutile; Anatase 1. Introduction Kaolins are widely used materials in the ceramic indus- try and in the manufacture of porcelain for electrotechnical devices, such as high voltage capacitors [1]. Kaolin content in compositions is often up to 50 wt%, but in the form of various mineral phases that contribute to the global material properties [2]. In particular, titanium minerals are mostly from kaolins, and they range from 1.3 wt% to 3.5 wt%. They are mostly in the form of anatase or minor quantities of rutile and brookite [3]. Kaolins containing anatase are widely used in compositions of electrotechnical porcelains since they improve dielectric properties [4,5]. Anatase has a tetragonal structure with irregular octa- hedra of oxygens, where Ti–O interatomic distances is about 1.917 ˚ A. Rutile structure is different with a tetra- gonal arrangement of cation and octahedral arrangement of oxygens around cations. Ti–O distances are about 1.959 ˚ A and Ti–Ti bonds are 2.96 ˚ A or 3.57 ˚ A [6]. In general, structural arrangement, cristallinity degree and size of anatase crystals strongly influence permittivity and dielectric loss, in the frequency range considered for dielectric porcelains. The relative permittivity of anatase phase was reported to be " r ¼ 48 for powders [7] and " r ¼ 40 for thin films [8]. Rutile phase was reported to be " r ¼ 89 along a-axis and " r ¼ 173 along c-axis due to its anisotropic nature. A value of " r ¼ 127 can be considered as an average [9,10]. With powder compacts, the apparent density, grain morphology and thermal treatment change progressively the microcrys- tal structure, and most effectively at temperature close to that of the anatase–rutile transformation. Particularly, the low frequency (1 kHz) dielectric constant of compressed TiO 2 powder of anatase exceed (" r =40–150) that of rutile (" r =8–15) [11]. After firing at temperature above 850 1C, the progressive transformation to rutile induces the decrease of " r down to 8–15 and a subsequent increase above 1150 1C of " r ¼ 18–25. Structural transformations are also determinant in dielectric loss, since anatase powder www.elsevier.com/locate/ceramint 0272-8842/$36.00 & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2012.06.053 n Corresponding author. Tel.: þ 213 793634550. E-mail address: nedjmabouzidi@yahoo.fr (N. Bouzidi).