Studies on barium titanate based 0-3 composites

Abstract

Fabrication and characterizations of barium titanate BaTiO3 based 0-3 composites are presented and discussed. Two types of composites are studied. First, barium titanate powder prepared by a mixed oxide route is dispersed into a poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) copolymer matrix to form ceramic/polymer composites. The second type of ceramic/ceramic composite is fabricated by mixing a sol-gel BaTiO3 powder into a BaTiO3 sol-gel matrix. BaTiO3/P(BDF-TrFE) 0-3 composites with various ceramic volume fractions are fabricated. The dielectric permittivity and loss of the 0-3 composites are measured as functions of temperature. These data are used to estimate the electric field experienced by the ceramic phase during poling and used to optimize the poling temperature. After the poling process, the pyroelectric and piezoelectric properties of the 0-3 composites were measured and compared to model calculations. The polarization distributions of the composites were also studied using the laser induced pressure pulse (LIPP) method. BaTiO3/BaTiO3 ceramic/ceramic composite filems are fabricated by a modified sol-gel process. Nano-sized BaTiO3 powder are dispersed in a BaTiO3 sol-gel matrix to form a 0-3 composite solution. Films are prepared by spin coating many layers (8 layers with thickness about 16 um) on stainless steel substrates and annealed at carious temperatures. The crystallization of the 0-3 composite film si studied by X-ray diffraction. The dielectric permittivity and the ferroelectric properties of the films are also measured. The major findings of the project included: (1) Barium titanate (BaTiO3) powders with size in the nanometer range were prepared by a sol-gel process and coprecipitation method. The average particle size of the powder prepared by a sol-gel process and coprecipitation method was 100 nm and 300 nm, respectively. BaTiO3 ceramic, with grain size >= 1 um, were prepared by sintering the sol-gel derived powder and the coprecipitation derived powder. The dielectric permittivity and the ferroelectric hysteresis loop were measured as functions of temperature. The room temperature (25 C) dielectric permittivity, pyroelectric and piezoelectric properties were also measured as functions of the poling field. The results will be submitted for publication. (2) Barium titanate/polyvinylidene fluoride-trifluoroethylene [BaTiO3/P(VDF-TrFE)] 0-3 composites with different volume fractions of ceramic were fabricated. The permittivities and electrical resistivities of the composites were measured as functions of temperature. These data were then used to find the electric field experienced by the ceramic phase and hence the optimum poling temperature. The pyroelectric and piezoelectric properties of the composites were measured and compared to model calculations. The results are published in Ferroelectrics, Vol.224, pp.113-120 (1999). (3) Barium titanate (BaTiO3) 0-3 ceramic/ceramic composite thick films (~16um) for ultrasonic transducer applications were fabricated by a modified sol-gel process. Nano-sized BaTiO3 powder was dispersed in a sol-gel matrix of BaTiO3 to form a 0-3 composite solution. Films were prepared by spin coating and then annealed at various temperatures. The crystallization of the composite film was studied by X-ray diffraction. The dielectric permittivity and the ferroelectric properties of the film were also measured. The results will be published in Proceedings 1999 Spring Meeting Symposium and in Nano Structured Materials.