Frenkel, Iakov Ilich

(also Frenkel). Born Jan. 29 (Feb. 2), 1894, in Rostov-on-Don; died Jan. 23, 1952, in Leningrad. Soviet theoretical physicist. Corresponding member of the Academy of Sciences of the USSR (1929).

Upon graduating from Petrograd University in 1916, Frenkel’ remained there to be trained for a professorship. From 1918 to 1921 he was a privatdocent at Tavrida University. In 1921 he was appointed head of the theoretical division of the Physicotechnical Institute and head of the subdepartment of theoretical physics of the Leningrad Polytechnic Institute.

Frenkel’ had an unusually broad range of interests, encompassing the electron theory of solids, the physics of the condensed state, the physics of the atomic nucleus, general problems of quantum mechanics and electrodynamics, astrophysics, geophysics, and biophysics. He contributed basic works in the quantum theory of solids. In 1917 he explained the phenomenon of contact potential difference on the basis of Bohr’s quantum theory and laid the foundations of the quantum theory of metals, showing that valence electrons in metals are collectivized and, at sufficiently high temperatures, do not contribute specific heat; his theory of “itinerant” electrons resolved the problem of the heat capacity of metals in the classical electron theory of metals. In 1927, Frenkel’ applied the concept of de Broglie waves to the motion of free electrons in metals and explained the relatively high “transparency” of metallic crystals to conduction electrons and the dependence of electrical conductivity on temperature and on the presence of impurities and various imperfections in the crystal lattice.

In 1928, by applying the Pauli exclusion principle to an electron gas, Frenkel’ constructed the theory of the spontaneous magnetization of ferromagnets (the model based on collectivized electrons), proposed the theory of white dwarfs, and determined the coercive forces in solids. In 1930, Frenkel’ and Ia. G. Dorf-man theoretically substantiated the breakup of a ferromagnet into domains. In 1931, Frenkel’ constructed the theory of the absorption of light in solid dielectrics and introduced the concept of the exciton. One of the creators of the current conception of the real crystal, he introduced the concept of defects of the crystal lattice (Frenkel defects) and worked out the theory of mobile dislocations (1938).

Beginning in 1924, Frenkel’ worked on the construction of the kinetic theory of liquids. His work in this area culminated in the monograph The Kinetic Theory of Liquids (1945; State Prize of the USSR, 1947). Frenkel’ worked out the theory of conventional and orientational melting, determined the hardness elements inherent in liquids, and developed the molecular theory of the yield of solids and the theory of diffusion and viscosity. In 1936–37 he introduced the concept of the temperature of atomic nuclei and worked out a statistical theory of heavy nuclei, and in 1939 he developed the electrocapillary theory of heavy nuclei (the Bohr-Frenkel’ liquid-drop model of the nucleus) and predicted their spontaneous fission. In 1946 he explained the phenomenon of the sintering of metal powders, which proved to be the theoretical foundation of powder metallurgy.

Frenkel’ is the author of the first complete course in theoretical physics in the USSR, comprising Theoretical Mechanics (1940), Statistical Physics (1933), Electrodynamics (vols. 1–2, 1934–35), and Wave Mechanics (vols. 1–2, 1933–34). He was awarded the Order of the Red Banner of Labor.