Debye, Petrus (Peter) Josephus Wilhelmus (1884-1966)

Dutch-born US physicist. A pioneer of X-ray powder crystallography, he also worked on polar molecules, dipole moments, molecular structure, and polymers. The Debye-Hückel theory, developed with German chemist Erich Hückel, concerns the ordering of ions in solution. Nobel Prize for Chemistry 1936. Debye was born in Maastricht and studied at the Technische Hochschule in Aachen, Germany, and at the University of Munich. He held a series of professorships in Switzerland and Germany, starting at Zürich 1910. In 1934 he went to the Max Planck Institute, Berlin. He was lecturing at Cornell University in the USA in 1940 when Germany invaded the Netherlands, so he remained at Cornell as professor 1940-52. Debye's first major contribution was a modification of Einstein's theory of specific heats to include compressibility and expansivity. Debye's studies of dielectric constants led to the explanation of their temperature dependence and of their importance in the interpretation of dipole moments as indicators of molecular structure. This earned him the Nobel prize, and the unit of dielectric constant is now called the debye. In crystallography he showed that the thermal motion of the atoms in a solid affects the X-ray interfaces and that randomly oriented particles can produce X-ray diffraction patterns of a characteristic kind. Powder X-ray diffraction analysis eliminated the need for large single crystals. In the 1930s Debye showed that sound waves in a liquid can behave like a diffraction grating.