STEPANOV, ALEKSANDR VASIL’EVICH

(b. St. Petersburg, Russia, 26 August 1908; d. Yalta, U.S.S.R., 16 May 1972)

physics.

Stepanov’s father, Vasilii Fedorovich Stepanov, was a building technician; his mother, Nadezhda Vasil’evna Bratanova, was a housewife. Stepanov graduated from the secondary school in Leningrad in 1925; a year before he had already started to work at the Leningrad Physical-Technical Institute, as an assistant in one of the radio engineering departments.

In 1925 Stepanov entered the Faculty of Physics and Mechanics at the Leningrad Polytechnical Institute, from which he graduated in 1930. Two years before graduation he joined Ivan Vasil’evich Obreimov’s laboratory at the Leningrad Physical-Technical Institute, and in 1930 he moved with Obreimov to the Ukrainian Physical-Technical Institute in Kharkov. There he worked for a short time. From 1931 until his death Stepanov served as a scientific fellow at the Leningrad Physical-Technical Institute and eventually became head of the laboratory of mechanical properties of crystals. At the same time he taught at the Faculty of Physics and Mechanics, where he also conducted experiments in the laboratory of optics directed by V. K. Fredericks. In 1937 he moved to the Pokrovskii Pedagogical Institute in Leningrad, where he lectured for the rest of his life. At this institute he founded the department of theoretical physics.

Stepanov’s early work in Obreimov’s laboratories was connected with optical methods of observing the stress state in crystals. He also participated in Obreimov and Lev Vasil’evich Shubnikov’s elaboration of an experimental technique for growing ideal crystals.

Beginning in the early 1930’s, Stepanov directed his efforts to the investigation of physical properties of crystals, especially their strength. The work of Abram Fedorovich Ioffe and his associates established the influence of surface (and internal) defects (scratches, cracks, holes) on crystal strength. Stepanov went farther, showing that the centers of brittle fracture arise within the body of the crystal because of stress due to plastic strain (shear, twinning), prior to fracture. This view of Stepanov’s (now generally accepted) did not originally receive support because it was commonly held that plastic strain results only in strengthening. Stepanov formulated and showed experimentally the existence of anomalously high thermal conductivity associated with the shear of boundary layers. He established the connection between the melting heat and the strain, and described the influence of plastic strain on electrical conductivity of ionic crystals. In 1933 he discovered the effect of slip-band electrification that occurs during plastic deformation of ionic crystals (in modern terminology, “charged dislocations”).

An important series of Stepanov’s investigations is related to the halides of silver and thallium and to alloys based on them. Stepanov demonstrated that their plastic behavior closely resembles that of metals, and therefore called them “transparent metals” (because the crystals are transparent). He grew large monocrystals of these aggregations and examined their properties in detail. He found, in particular, that the mutual polarization of ions decreases electrical conductivity, and thus influences plastic properties. (During numerous sessions and seminars, Ioffe, the director of the Leningrad Physical-Technical Institute, would ring a bell made of silver chloride that Stepanov had presented to him.) These investigations formed the bases of Stepanov’s candidate thesis (1937) and doctoral dissertation (1939).

Producing artificial damages on the surface of the examined crystals, Stepanov observed the dynamics of shear formation (using the optical polarization method for studying the stress state). He examined the transformation of microslips to macroshear and demonstrated that this process of unification starts not only with the achievement of a certain stress level but also at a certain temperature.

In the early 1960’s Stepanov and his colleagues started to investigate mechanical properties of solids at liquid helium temperatures. During these pioneering experiments a number of new effects were discovered: the modifications of the character of a fracture, the time variation of a fracture diagram, and the plastic strain of ionic crystals at liquid helium temperatures. These results are important today for work in space. Stepanov’s laboratory also carried out experiments with threadlike crystals (whiskers).

In the late 1940’s Stepanov investigated mechnical properties of wood and bone, whose structure accounts for a sharp anisotropy of elastic and strength properties. The anisotropy impedes the growth of fracture and may form a basis for creation of highly durable materials. Stepanov’s work in this field is rightly considered pioneering in the development of composite materials.

In the late 1940’s Stepanov developed a method of forming solid objects immediately from the melt, known in literature as “Stepanov’s method.” His idea was not to use the conventional methods of forming solid objects (such as rolling, pressing, and drawing). He argued that it might be possible to obtain these objects immediately from a liquid metal, but that it would be necessary to overcome the typical property of any liquid (including metal) not to conserve its shape. He showed that under suitable conditions, the capillary forces may promote sustaining the “prescribed” shape of a liquid mass set free in space and without any mechanical support. As early as the late 1940’s Stepanov obtained in this way monocrystal plates of zinc, aluminum, bismuth, and other materials. This method, a modification of the earlier Chokhralskii method, made it possible during Stepanov’s life to stretch solid articles of a required shape directly from the melts of aluminum, copper, iron, halides, and semiconductor materials (first of germanium and silicon, and later of more complex semiconductor aggregations). This stretching was produced by the capillary mechanism of shape formation under specific conditions of heat and velocity. The foundations of this method and the history of its discovery and development are discussed in Stepanov’s book Budushchee metalloobrabotki (1963). Practically each year since 1968, All-Union meetings on Stepanov’s method of obtaining semiconducting materials have been held at the Leningrad Physical-Technical Institute. The proceedings of these meetings are usually published in physical journals and special collections.

In recognition of his scientific achievements, the U.S.S.R. Academy of Sciences elected Stepanov a corresponding member in 1968. Stepanov, who never married, loved music and was a skilled amateur tennis player and skier on both snow and water. Hoping to enjoy some water skiing, he took a short leave in the spring of 1972 and went to the Crimea, where he died of a heart attack.

BIBLIOGRAPHY

I. Original Works. “Über den Zusammenhang der Deformationsarbeit mit der Schmelzwärme,” pt. 1, in Physikalische Zeitschrift der Sowjetunion, 2 (1932), 537–543, and “Über den Mechanismus des plastischen Deformation,” pt. 2, ibid., 5 (1935), 706–713; “Grundlagen der Theorie der praktischen Festigkeit,” in Zeitschrift für Physik, 92 , Heft 1–2 (1934), 42–60; “Artificial Slip Formation in Crystals,” in Nature, 140 (1937), 64; “lavlenie iskusstvennogo sdvigoobrazovaniia” (The phenomena of artificial shearing), pt. 1, in Zhurnal eksperimentalnoi i teoreticheskoi fiziki, 17 , no. 7 (1947), 601, pt. 2, ibid., 18 no. 8 (1948), 741–749, pt. 3, written with E. A. Mulkamanovich, ibid., no. 9 (1948), 773–775, pt. 4 ibid., 21 , no. 3 (1951), 401–408, pt. 5, written with E. A. Mulkamanovich, ibid., 409–412, and pt. 6, written with E. A. Mulkamanovich, in Fizika tverdogo tela, 1 , no. 4 (1959), 666–670; “Iskusstvennaia anizotropiia kak sredstvo pridaniia izdeliiam trebuemykh mekhanicheskikh svoistv” (Artificial anisotropy as a means for giving an article required mechanical properties), in Sbornik posviashchennyi semidesiatiletiiu akademika A. F. loffe (Memorial volume dedicated to Academician A. F. loffe on the occasion of his seventieth birthday; Moscow, 1950), 341–354; “Ob elektrostaticheskoi teorii ionnykh kristallov” (On the electrostatic theory of ionic crystals), in Zhurnal eksperimentalnoi i teoreticheskoi fiziki, 34 , no, 6 (1958), 1661–1662; Budushchee metalloobrabotki (The future of metal treatment; Leningrad, 1963); “O vliianii sostoianiia poverkhnosti na skachkoobraznuiu deformatsiiu aluminiia pri T 1, 3 K” (On the influence of the state of surface on a ‘jump–type’ deformation of aluminum at 1, 3 K), in Fizika metallov i metallovedenie, 17 , no. 4 (1964), 502; “Poluchenie monokristallov opredelenoi formy” (On the formation of monocrystals of a certain form), in Materialy pervogo soveshchaniia po polucheniiu poluprovodnikovykh monokristallov sposobom Stepanova i perspektivam ikh primeneniia v priborostroenii (Leningrad, 1968), which contains a total of fourteen papers written by Stepanov and his colleagues; “O dlinne probega dislokatsii v kristallakh ftoristogo litiia pri gelievikh temperaturakh” (On the length of dislocation of free path in LiF crystals at helium temperatures), in Dinamika dislokatsii (The dynamics of dislocations; Kharkov, 1968), which contains two other papers by Stepanov on the same subject; “Deformation of Alkali-Halide Crystals at Liquid Helium Temperatures,” in Second International Conference on the Strength of Metals and Alloys (Metals Park, Ohio, 1970), 235; and Osnovy prakticheskoi prochnosti kristallov (The foundations of the practical strength of crystals; Moscow, 1974).

II. Secondary Literature. Obituaries are in Kristallograftia, 17 , no. 5 (1972), 1087–1088, English trans. in Soviet Physics: Crystallography, 17 , no. 5 (1973), 970–971; and Izvestiia Akademii nauk, seriia fizicheskaia, 37 , no. 11 (1973), 2250–2253. See also V. J. Frenkel, G. V. Kurdiumov, and M. V. Klassen-Nekliudova, “Aleksandr Vasilievich Stepanov,” in Materialy k biobibliografii uchenikh SSSR (Moscow, 1976).

V. J. Frenkel