Synthesis and characterization of Ca 1-X Sr x Cu 3 Ti 4 O 12 thin films for dielectric applications

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Synthesis and characterization of Ca1-X SrxCu3Ti4O12 thin films for dielectric applications R. Guzman, M.S.Tomar, R.E. Melgarejo, Physics Department, University of Puerto Rico, Mayagüez, PR 00681-9016, and R.S. Katiyar, Physics Department, University of Puerto Rico, San Juan PR 00931-3343

ABSTRACT There is a great deal of interest in CaCu3Ti4O12 system for dielectric applications. We have studied Ca1-xSrxCu3Ti4O12 system for different compositions. The material is synthesized by sol-gel chemical solution route and thin films were deposited by spin coating. Thin films were investigated by x-ray diffraction and Raman spectroscopy for structural properties. These results indicate a solid solution for the compositions x = 0.00 to 0.80. The SEM micrographs shows the uniform films at 800o C, but the dielectric response of Ca1-xSrxCu3Ti4O12 (x = 0.00) shows the dielectric constant value below 200.

INTRODUCTION A2/3Cu3Ti4O12 and BCu3Ti4O12 family of materials [1], where A and B are trivalent and divalent cations, respectively, are of great interest for their dielectric and microwave applications. The complex perovskite compounds CaCu3Ti4O12 (CCTO) has attracted considerable attention due to its high dielectric response. At lower frequencies the dielectric constants near 16,000 for ceramics and 80,000 for single-crystal samples [2-4], which are nearly constant over a wide temperature range (100 - 600 K). In addition, the study [4] also shows that above the frequency range between 102 Hz and 106 Hz, the dielectric constant drops to about 100. Large dipole moments in some perovskite like materials are due to ionic displacements within the centro-symmetric structures, but Raman scattering studies [5] of CCTO indicates no structural phase transition between 20 and 600 K, and recent first principle calculations [6] suggests extrinsic origin for the anomalous low-frequency dielectric response. Although bulk CCTO materials have been extensively investigated, thin films are required for electronic applications. In addition, if Ca ion is replaced by divalent ion, the dielectric and structural behavior may change. We report on the synthesis of Ca1-xSrxCu3Ti4O12 thin films prepared by sol-gel process for various compositions and their structural and dielectric response.









Cu(OOCCH3)2.H2O and Ti[OCH(CH3)2]4 were used as precursors. The appropriate amount of the salts were mixed individually in 2-Ethylhexanoic acid and mixed hot to make stoichiometric solution. Both powder and films were prepared by proper sol-gel process. Thin films were deposited on Pt substrate (Pt/TiO2/SiO2/Si) by spin coating at 3000 rms. Each layer was annealed at 300° C for 10 min with total of 20 layers. Total film thickness, measured by optical method, was 0.75 µm. Finally, the thin film samples were post annealed for one hour at 750° C. The powder samples were annealed at the temperatures ranging from 600° C to 800° C for 4 hours.