ALTERNATING AND DIRECT-CURRENT FIELD EFFECTS ON THE DIELECTRIC RESPONSE OF LA-MODIFIED LEAD-ZIRCONATE-TITANATE

The complex dielectric responses of various La-modified lead zirconate titanate ceramic specimens have been measured under various ac drive and de bias conditions. Investigations were performed for different La concentrations on specimens with Zr/Ti ratios of 40/60 and 65/35. The se investigations demonstrated that the influence of increasing ac dri ve and de bias are in opposition: increasing drive results in an incre ase in the dielectric constant, whereas increasing bias results in a d ecrease. Investigations as a function of La content revealed a strong decrease in the ac-induced nonlinearities with increasing La content i n the compositional range near a crossover between micron-sized domain s and tweedlike structures. The ac drive dependent dielectric data wer e then empirically fitted to a power series expansion in the ac field. An anomalous change in sign of the second-order nonlinearity was foun d for lower La-content compositions near the temperature of the dielec tric maximum. It is believed that this change in sign results from a s uppression of ferroelectric order and the stabilization of a paraelect ric state at temperatures close to the ferroelectric phase transformat ion. (C) 1997 American Institute of Physics.