Thesis (M.Sc.)--Chulalongkorn University, 1998

There is currently widespread interest in developing a range in electronic devices exploiting the ferroelectric, pyroelectric and piezoelectric properties of modified PbTiO3 ceramics. In this research the effects of La3+ and Ca2+ on microstructure, ferroelectric and dielectric properties of PbTiO3 bulk ceramics were investigated. La3+ and Ca2+ modified PbTiO3 were prepared from mixing of lead oxide, titanium oxide, lanthanum oxide, calcium carbonate and then calcining and sintering at 1200 ํC. The results indicated that various compositions in the system of Pb1-x Lax Ti1-x/4 O3 up to x = 0.2 and Pb1-x Cax TiO3 up to x = 0.3 exhibited to induce crystallization to the tetragonal perovskite phase. Microscopy revealed increasing grain size from 0.5 to 5 mum without cracks when La3+ concentration for Pb1-x Lax Ti1-x/4 O3 was increased. But Pb1-x Cax TiO3 ceramics with increasing Ca2+ contents showed decreasing in grain sizes ranging from~100 to~20~2 mum. Cracks were observed in all samples, except Pb0.7 Ca0.3 TiO3 composition. XRD analysis of all samples indicated that La3+ and Ca2+ substitution for Pb2+ resulted in decreasing in the tetragonal distortion of the PbTiO3 unit cell. The polarization-electric field response, the dielectric constant and dielectric loss of all compositions were measured. The ceramics showed a variation in electrical properties dependent on the amount of La3+ and Ca2+ substitution. But Pb1-x Lax Ti1-x/4 O3 with X = 0.2 exhibited higher conductive characteristic. The Curie points of Pb0.85 La0.15 Ti0.9625 O3 and Pb0.85 Ca0.15 TiO3 ceramics were ~280 ํC and ~255 ํC, respectively.