Synthesis, characterization and properties of PZT materials modified with Nd. Part I. Processing of precursor powders.

A very simple <<Ceramic Processing>> synthesis method has been developed fo r lead zirconate titanate (PZT) materials modified with Nd (PNZT), using th e most up-to-date synthesis processing methods such as the sol-gel procedur e. Nd3+ (it is supposed to replace Pb2+), has been chosen as modified becau se its size is near to Pb2+ than other possibles modifier elements. The qua ntity of neodymium used ranged from 6 to 10% in moles and the Zr/Ti ratio i n the four prepared ceramics was 0.56 to 3 moles (these differ only one mol of Zr, see Table I). To control the stoichiometry of the precursor powders , the parameters which have the greatest influence on the final result were determined as accurately as possible so that optimum results could be achi eved: precipitation pH (0.5-1), precipitation temperature (30-34 degrees C) , relative humidity over the synthesis system (85%), degree of mechanical a gitation of the reactive system (around 800 rpm), aging temperature (approx imate to 5 degrees C) and aging pH((10-11)). Lyophilization (drying of precursor powders suspended in acetone in liquid nitrogen at a temperature of -197 degrees C) has been introduced in this pr ocessing method to dry the precipitate in the synthesis of the precursor po wders. This avoids the loss of part of the products which may occur when wa shing is used and, thereby, allows the chosen stoichiometry to be achieved. This technique also avoids the contaminating steps of oven-drying and mill ing and results in very loose powders of nanometric size, qualities which a re fundamental for good ferroelectric and/or piezoelectric properties. The synthesis process has been shown to occur as a fractional precipitation , and not as coprecipitation with the formation of an oxalate compound. The results demonstrated the excellent reproducibility both of the stoichiomet ries, with an error less than 10(-3) mg/ml, and of the size of the lyophili zed particles (0.2-0.4 mu m).