Ferroelectricity: The Foundation of a Field from Form to Function
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Ferroelectricity:
The Foundation of a Field from Form to Function
R.E. Newnham and L. Eric Cross Abstract This article highlights the major role Arthur von Hippel and the Laboratory for Insulation Research at the Massachusetts Institute of Technology played in the early development of the field of ferroelectricity in mixed oxides with the perovskite structure and, in particular, in the identification of ferroelectricity in barium titanate following its discovery in industrial laboratories in the United States during World War II. Very early optical and x-ray studies highlighted the characteristics of the ferroelectric domain structures in both ceramic and single-crystal BaTiO3, the elimination of domains at the Curie temperature TC, and the salient characteristics of the two low-temperature phase transitions. Perhaps the culmination of this work was the detailed studies of lamella 90° domains by Peter Forsbergh and the gorgeous patterns these could generate. This article also traces the manner in which the early studies contributed to whole industries based on perovskite ferroelectrics. The ceramic capacitor industry is now fabricating sophisticated, cofired multilayer capacitors (MLCs) with up to a thousand 1-µm-thick dielectric layers interleaved with base metal electrodes, addressing a market for some 1013 capacitors per year. Manufacturers of large piezoelectric transducers depend almost exclusively on perovskite-structure oxide ceramics. Navy sonar systems are major customers, but spinoff has occurred into a wide range of commercial and medical ultrasound systems. The capability of current materials has improved more than tenfold over the original BaTiO3 ceramics as a result of the effective application of molecular engineering, a strong testament to the insight of the founder of this area of study. Keywords: Arthur von Hippel, barium titanate, BaTiO3, capacitors, ferroelectric, interdisciplinary, Massachusetts Institute of Technology, materials research, MIT, perovskite, transducers.
Ferroelectricity Ferroelectricity is perhaps even today almost as much an art as it is a science. During the last 60 years, ceramists have identified hundreds of new ferroelectric oxides with many important applications. Ferroelectricity involves a complex interplay of electrical, mechanical, and thermal effects near a displacive phase transformation. On cooling through the phase transition, the symmetry is lowered and beautiful polar domain patterns are observed in the low-temperature ferroelectric state.
MRS BULLETIN • VOLUME 30 • NOVEMBER 2005
Ferroelectricity is defined as a physical phenomenon in which a spontaneous electric dipole moment can be reoriented from one crystallographic direction to another by an applied electric field. The reorientation process involves two or more domain states within the crystal (or within individual grains in a ceramic). The key experiment is the existence of a hysteresis loop between polarization and electric field, analogous to the ferromagnetic hysteresis loop between magnetization an
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