Barrier Layers Formation in Tin Substituted Calcium Copper Titanate CaCu 3 Ti 4x Sn x O 12 (0  x  1:0) Om PARKASH  , Bhoomika YADAV, Prakash SINGH and Devendra KUMAR Department of Ceramic Engineering, Institute of Technology, Banaras Hindu University, Varanasi-221005, India (Received March 26, 2006; accepted July 19, 2006; published September 11, 2006) A few compositions in the system CaCu 3 Ti 4x Sn x O 3 (0  x  1:0) were synthesized by solid state diffusion controlled thermochemical process. Powder X-ray diffraction patterns of all the compositions show that these compositions are single phase solid solution. All the samples have cubic crystal structure similar to undoped CaCu 3 Ti 4 O 12 . Microstructure shows that average grain size is about 10 mm. Dielectric measurements have been carried out in the temperature and frequency range 300 – 450 K and 1 kHz– 1 MHz, respectively. It has been shown by complex plane impedance and modulus analysis that barrier layers form at grain boundaries in these materials. These barriers impart high value of dielectric constant to the resultant ceramic. Dielectric constant, " r can be enhanced and dielectric loss (loss tangent), D can be reduced further by chemical infiltration. KEYWORDS: perovskite oxide, calcium copper titanate, dielectric behaviour, barrier layer capacitors DOI: 10.1143/JPSJ.75.094717 1. Introduction For high dielectric constant, compositions based on barium titanate, BaTiO 3 are normally used. 1,2) The limitation of these materials is their high temperature coefficient of capacitance near their Curie temperature, which can be shifted suitably by modifying the composition. In recent years, it has been reported that calcium copper titanate, CaCu 3 Ti 4 O 12 having perovskite structure has very high value of dielectric constant (10 5 at 1 kHz and 300 K) which remains almost temperature independent in the temperature range 300 – 600 K. 3–6) This makes this material useful as a thermally stable high dielectric constant material in a wide variety of electronic devices. It also has very high potential for applications in devices in thick and thin film forms. 7) It has been reported that this material is not ferroelectric. High value of dielectric constant is attributed to formation of barrier layers at grain boundaries. 8–10) This has been shown by impedance analysis that grain boundaries are much more resistive as compared to the grains. Effect of a large variety of substitutions on dielectric behaviour has been reported. 4) In the present paper, the effect of tin substitution at titanium site has been investigated which is an isovalent substitution. Tin is also used in BaTiO 3 to get thermally stable capacitors. 1,2) Immittance analysis has been used to analyze and interpret the results obtained experimentally. 2. Experimental Various compositions with x ¼ 0:0, 0.1, 0.2, 0.4, 0.5, and 1.0 were prepared in the system CaCu 3 Ti 4x Sn x O 12 by solid state ceramic route. Analytical Grade (AR) compounds CaCO 3 , CuO, TiO 2 , and SnO 2 having purity better than 99.5% were used as starting raw materials. Appropriate quantities of these materials were weighed and mixed for 6 h in a ball mill in agate jars using agate spherical balls as grinding media and acetone as mixing media. After drying the mixed and ground powder at 373 K in an oven, it was calcined in a platinum crucible at 1273 K for 10 h and then furnace cooled. The calcined powders were once again ground and mixed to homogenize the powder and reduce the particle size. A few drops of 2% polyvinyl alcohol solution were mixed with powder as binder. Powder was then pressed in a stainless steel die into pellets of diameter 12 mm and thickness 1– 2 mm. The pellets were heated slowly (2 K/ min) to 873 K in a programmed furnace and soaked for an hour to burn off the binder. Temperature was then raised to 1348 K at the rate of 5 K per minute and samples were sintered at this temperature for 20 h. After sintering, the samples were furnace cooled. One of the pellet was crushed for powder X ray diffraction. Powder X-ray diffraction (XRD) was done employing Rigaku ID 3000 Diffractometer using Cu-K radiation and a Ni filter. Bulk density was determined using Archimedes’s principle. Percentage open porosity was calculated using the relationship: Bulk density ¼ Weight of the sample in air ðWeight of the sample in air  Weight of the sample in waterÞ Open porosity ¼ ðTheoretical density  Bulk densityÞ Theoretical density  100  E-mail: opec_itbhu2003@yahoo.co.in Journal of the Physical Society of Japan Vol. 75, No. 9, September, 2006, 094717 #2006 The Physical Society of Japan 094717-1