Piezoelectric applications of ferroelectrics

The utility of ferroelectrics for piezoelectric devices rests on two characteristics, asymmetry and high dielectric constant. In one type of ferroelectric crystal, including Rochelle salt, asymmetry is intrinsic in the structure. Substances which owe their piezoelectric effect to ferroelectric polarity are of particular utility because domain orientation by electric field imparts piezoelectric response to polycrystalline bodies. Once this orientation has been achieved one usually desires to have a minimum of the nonlinearity, hysteresis losses, and high temperature coefficients connected with ferroelectricity. This has been achieved with modified barium titanate and especially lead titanate zirconate ceramics. Use of piezoelectric transducers in electroacoustics and ultrasonics has kept pace with the general growth in these fields, especially in phonograph pickups, industrial ultrasonics, and underwater acoustics. Piezoelectric spark sources for gas lighting are becoming a substantial consumer item. Piezoelectric ceramic IF filters both for 455 kHz and 10.7 MHz are of increasing interest due to their ruggedness and small size compatible with transistor and integrated circuitry.