3.4 Piezoelectric materials synthesis

This module was developed as part of the Rice University course CHEM-496: Chemistry of Electronic Materials . This module was prepared with the assistance of Ilse Y. Guzman-Jimenez.

Introduction

Piezoelectricity is the generation of an electric moment by a change of stress applied to a solid. The word piezoelectricity literally means “pressure electricity”; the prefix piezo is derived from the Greek word piezein , “to press”. The piezoelectric effect was discovered in 1880 by the brothers Jacques and Pierre Curie. Not only did they demonstrate the phenomenon, but they also established the criteria for its existence in a given crystal. Of the thirty-two crystal classes, twenty-one are non-centrosymmetric (not having a centre of symmetry), and of these, twenty exhibit direct piezoelectricity.

The first practical application of the piezoelectric effect was developed when ground quartz crystals were placed between the plates of a tuning capacitor in order to stabilize oscillating circuits in radio transmitters and receivers; however, the phenomenon of piezoelectricity was not well exploited until World War I, when Langevin used piezoelectrically excited quartz plates to generate sounds waves in water for use in submarine detection.

Piezoelectricity can also occur in polycrystalline or amorphous substances which have become anisotropic by external agents. Synthetic piezoelectric materials became available near the end of World War II, with the accidental discovery of the fact that materials like barium titanate and rare earth oxides become piezoelectric when they are polarized electrically. During the postwar years, when germanium and silicon were revolutionizing the electronics industry, piezoceramics appeared for a while to be joining the revolution, but the limited availability of materials and components, made the piezoelectric phenomenon failed to lead mature applications during the 1950s. It is only now that a variety of piezoelectric materials are being synthesized and optimized. As a consequence piezoelectric-based devices are undergoing a revolutionary development, specially for medicine and aerospace applications.

Piezoelectric ceramics

Most piezoelectric transducers are made up of ceramic materials for a broad range of electromechanical conversion tasks as transmitters, ranging from buzzers in alarm clocks to sonars, and as receivers, ranging from ultra high frequency (UHF) filters to hydrophones.

Most of the piezoelectric materials in usage are from the lead zirconate titanate (PZT) family, because of their excellent piezoelectric parameters, thermal stability, and dielectric properties. Additionally the properties of this family can be modified by changing the zirconium to titanium ratio or by addition of both metallic and non-metallic elements. PZT (PbZr _1-x Ti _X O ₃ ) ceramics and their solid solutions with several complex perovskite oxides have been studied; among the various complex oxide materials, niobates have attracted special attention. Ternary ceramic materials, lead metaniobate, as well as, barium and modified lead titanates complete the list of piezoceramic materials.