Debye, Peter Joseph William

Peter Joseph William Debye (24.03.1884—2.02.1966) was a physicist and chemist and one of the founders of the theory of the solid state. He was born in Maastricht. He graduated from the Higher Technical School in Aachen (1905) and the University of Munich (1908). In 1911 he was professor at the University of Zurich, in 1912 at Utrecht, in 1913—20 at Göttingen, in 1920—27 at the Zurich Polytechnic, and in 1927—33 at the University of Leipzig. In 1934—39 he was director of the Kaiser Wilhelm Institute of Physics and professor at the University of Berlin, and in 1940—50 professor at Cornell University (USA). His research concerned the quantum theory of solids, the theory of the heat conduction of crystals, the theory of the structure of molecules and the quantum theory of the atom. In 1912 he introduced the idea of a solid as an isotropic elastic medium able to vibrate over a finite range of frequencies (the Debye model of a solid) and calculated the spectrum of natural frequencies for a regular crystal. From the form of the spectrum in the region of low frequencies he showed that the heat capacity of the lattice at low temperatures must be proportional to the third power of the absolute temperature (the Debye heat capacity law). Within his model he introduced the concept of a characteristic temperature (the Debye temperature), which for each substance determines the region where quantum effects become significant. He developed the theory of the heat conduction of dielectric crystals and the dipole theory of dielectrics, based on the idea of molecules as rigid dipoles. Independently of L. Brillouin he predicted (1913) the diffuse scattering of X-rays by lattice vibrations. In 1916, together with A. Sommerfeld, he applied the quantisation conditions to the explanation of the Zeeman effect and introduced the magnetic quantum number; together with P. Scherrer he developed a method of studying the structure of finely crystalline materials with the help of the diffraction of X-rays (the Debye–Scherrer method). In 1923 he explained the Compton effect. In 1926, independently of W. Giauque, he proposed the adiabatic demagnetisation of paramagnets as a way of obtaining temperatures below 1 K (the method of magnetic cooling). In 1932 he detected the diffraction of light by ultrasound. Together with E. Hückel he developed (1923) the theory of strong electrolytes, which explains the form of the dependence of the activity coefficient on concentration (the Debye–Hückel formula). He was one of the first to begin the study of polymers. A member of many academies of sciences and scientific societies and a foreign member of the USSR Academy of Sciences (1924). Nobel Prize in Chemistry (1936). The Lorentz, Faraday, Rumford, Franklin, Gibbs (1949), Planck (1950), Nichols and Priestley (1963) medals.