Yoshio Yoshikawa

Preparation of PLZT powders from several aqueous solutions

Fine, soft agglomerate and chemically homogeneous PLZT powders were prepared from nitrate, chloride and alkoxide precursors. The preparation is based on a coprecipitation method in which the aqueous clear solution of multicomponent systems is reacted with ammonia gas at the liquid surface. As-dried powder characteristics — the microstructure of agglomerates, colour and X-ray diffraction structure — were similar in all cases; however, the properties of calcined powders and of “two-stage” sintered pellet were affected not only by precursors, but also by postprecipitation processing: (a) washing with organic solvent, (b) drying and ageing, (c) calcining. A novel lattice behaviour, i.e. decomposition and recovery of perovskite structure of calcined powders regardless of precursors, was found over a wide temperature range from room temperature to 1150° C. Transparent ceramics were fabricated by sintering the acetone washed-aged powder derived from TiO(NO3)2 precursor.

Chemical preparation of Pb(In1/2Nb1/2)O3 powders

Abstract A chemical preparation method was applied to the synthesis of lead indium niobate (Pb(In1/2Nb1/2)O3, (PIN)) powders from nitrate solutions. As a niobium source, an oxalate-free niobium precursor solution was prepared from niobium hydrogen oxalate. Clear PIN precursor solutions with Pb2+, In3+ and peroxo–Nb ions were hydrolyzed with aqueous ammonia solutions. Coprecipitates with a high degree of compositional homogeneity were obtained through the control of the hydrolysis conditions. The as-prepared powders were amorphous and consisted of very small particle size (∼30 nm). The powders began to crystallize into a cubic pyrochlore phase at 500°C, formed a cubic perovskite phase at 700°C, and yielded a single-phase perovskite at 900°C.

Susceptibility to agglomeration of fine PLZT powders prepared from nitrate solutions

Abstract PLZT powder which has various degrees of agglomeration was prepared from an aqueous nitrate solution by three hydrolysis methods. They were fine, chemically homogeneous and amorphous. Their particle morphologies, however, were very different due to the different physico-chemical precipitation conditions. Addition of hydrogen peroxide, and a liquid-gas interface reaction were the most effective methods for producing a weakly agglomerated powder by hydrolysis.

Crystallization behavior of PZN–PFN powders from nitrate solutions

Abstract A series of x Pb(Zn 1/3 Nb 2/3 )O 3 ·(1− x )Pb(Fe 1/2 Nb 1/2 )O 3 powders were chemically prepared from nitrate solutions by hydrolysis with diethylamine as the precipitation reagent. The as-dried powders were amorphous and consisted of fine particles. The chemical composition of the as-dried powders was homogeneous so that the perovskite and pyrochlore phases were directly crystallized from the amorphous powders at 450∼600°C. The amount of the perovskite phase increased with increasing temperature and decreasing x value. For the x ≦0·4 powders, the perovskite phase was dominant and stable below 600°C, while for the x ≧ 0·5 powders, the pyrochlore phase was dominant and stable. Above 600°C, both phases were formed by some solid-state reactions. The thermodynamical relevance of the stability of the perovskite phase to temperature and composition is discussed.

Chemical Preparations and Two-Stage Sintering of PLZT

Soft agglomerate, fine particle size and amorphous PLZT powders are prepared from nitrates solutions. The effects of postprecipitation processing (washing, drying, raw powder aging and calcining temperature) on powder characteristics and on final densification are examined. Solid state reactions occur above 500°C and both PLZT and PbO phase appear on XRD-profiles. The Crystalline states of these PLZT and PbO are subjected on the above processing. A two-stage sintering is made with various processed powders. The application of acetone washed-aged raw powder and of calcination below 700°C is promissing to obtain fine PLZT ceramics.