ON RESEARCH IN SOLID-STATE PHYSICS AT TOMSK POLYTECHNIC INSTITUTE

V. A. SOKOLOV

Research in solid-state physics in Tomsk is traditional. The beginning of this research was laid by the works of Professor B. P. Weinberg, who worked at the Tomsk Technological (now Polytechnic) Institute from 1909 to 1924. In 1917–24, also at the Tomsk Technological Institute, V. D. Kuznetsov—then an instructor in the Department of Physics, and later an academician—began his first investigations; having become interested, under the influence of B. P. Weinberg, in problems of solid-state physics, he subsequently created at Tomsk University his own school of solid-state physics, widely known in the USSR and abroad.

Already in the first years of Soviet power, V. I. Lenin set a course toward creating in the country an extensive network of scientific-research centers. In 1923, a Scientific-Research Institute of Applied Physics was organized at the Tomsk Technological Institute (director—Prof. I. A. Sokolov). B. P. Weinberg, V. D. Kuznetsov, A. N. Dobrovidov, and others took part in the institute’s work; the main direction of the work was connected with the needs of solid-state physics. In 1928 the Institute of Applied Physics was transformed into the Siberian Scientific-Research Physico-Technical Institute (SFTI) and attached to Tomsk State University. For more than 30 years V. D. Kuznetsov was the permanent director of SFTI.

The works of Acad. V. D. Kuznetsov and his Tomsk pupils (Prof. M. A. Bolshanina and others) are devoted to the study of the surface energy of crystals, internal friction, diffusion, plasticity and strength of metals, the study of the mechanism of crystallization, external friction and wear of metals, and their machining by cutting. The principal direction of these works is the mechanical properties of solids. In the 1930s, under the direction of Prof. P. S. Tartakovsky, work on the study of the electrical properties of solids (dielectrics) was also being carried out in parallel at SFTI under TSU. Among these works, studies of the internal photoelectric effect in dielectrics became especially well known.

In 1938, after P. S. Tartakovsky left Tomsk, investigations of the electrical properties of solid dielectrics were expanded

at Tomsk Polytechnic Institute by a student of P. S. Tartakovsky, Professor A. A. Vorob’ev. The main direction of these works at that time was the study of the electrical strength of dielectrics. At the same time, at the Siberian Physico-Technical Institute, under the direction of Prof. K. A. Vodop’yanov, studies were being conducted of dielectric losses in dielectrics. Soon A. A. Vorob’ev organized at Tomsk Polytechnic Institute a broad front of research not only into the electrical properties, but also into other physicochemical properties of solid dielectrics. Thus arose the Siberian school of dielectric physics.

The front of work on the study of solid-state physics at Tomsk Polytechnic Institute was expanded still further in the last 5–6 years in connection with the organization of the Problem Laboratory of Electronics, Dielectrics, and Semiconductors (EDiP) (scientific director—Prof. A. A. Vorob’ev).

The creation of this laboratory, with the equipment and staff of scientific-support personnel assigned to it, made it possible not only to strengthen the lines of work previously existing at TPI in the study of the properties of solids (electrical strength, mechanical and thermal properties of dielectrics), but also to open new directions of research, such as: electronics and energetics of ionic structures, the action of radiation on solid materials, solid-state chemistry, and luminescence of dielectrics and semiconductors.

Let us now dwell on some concrete results of work in solid-state physics carried out at Tomsk Polytechnic Institute.

As a result of experimental investigations of the electrical properties of dielectrics, A. A. Vorob’ev, together with E. K. Zavadovskaya, developed and refined the ionization theories of electrical breakdown and showed that the electrical strength of crystals increases with an increase in lattice energy. A theory consistent with experiment was proposed, establishing a regular dependence of the electrical strength of crystals on lattice energy and on the duration of voltage application. Further development of the theory of electrical breakdown on the basis of ideas about impact ionization by electrons led A. A. Vorob’ev and his pupils G. A. Vorob’ev, V. A. Kostrygin, and others to an irrefutable experimental confirmation of the idea, earlier expressed by Academician A. F. Ioffe, concerning the strengthening of dielectrics in thin layers. This again, and quite realistically, placed on the agenda the question of the possibility of creating thin-layer high-strength insulation.

As a result of the development (under the direction of G. A. Vorob’ev) and application at TPI of special generators that make it possible to obtain high-voltage pulses of various durations down to \(10^{-10}\) sec, it has recently been possible to trace very fine details of the development of a discharge in space and time, and to establish interesting analogies in the mechanisms of discharge in gases and solids (such analogies followed from the ionization theory of breakdown). Thus, for example, the dependence of discharge time on thickness for a number of ionic crystals is analogous to the corresponding dependence for gases. It has been established that in solid dielectrics, just as in gases, at a certain small critical interelectrode distance, one breakdown mechanism is replaced by another (in gases this is the transition from a streamer discharge to a Townsend discharge; in crystalline dielectrics, from avalanche-streamer to multi-avalanche-streamer).

Electrical strength is not the only practically important property of a material. As was already noted, electrical

strength is a function of the lattice energy and increases as the latter increases. It should be noted that, as has been shown in works carried out under the direction of A. A. Vorob’ev and E. K. Zavadovskaya, not only the electrical strength but also the mechanical, thermal, and chemical strength likewise increase with increasing energy of the crystal lattice.

In recent years, in connection with the demands of atomic power engineering, radiation strength—or, as it is now customary to say, the radiation resistance of materials—has acquired ever greater importance.

Here again it is of interest to note that, as a result of a series of works carried out in our problem laboratory under the direction of Prof. E. K. Zavadovskaya, it has been shown that the radiation resistance of crystals, like their electrical strength, is also regularly related to the chemical composition of the crystals and to the energetic bonds existing in them, quantitatively determined by the magnitude of the lattice energy.

The dependence of the nature of the interaction of radiation with a substance on the chemical composition of the latter is already clearly manifested in the example of its absorbing capacity, which is of especially great importance for materials used as radiation shields.

Thus, for example, it has been established that, up to radiation energies of 30 MeV, the attenuation coefficients of corpuscular and electromagnetic radiation in alkali-halide crystals, depending on chemical composition, increase with increasing atomic number of the elements making up the compounds.

The depth of penetration into a substance of corpuscular radiations also depends on its chemical composition. Experimental studies by B. A. Kononov and V. N. Rudenko for electrons with energies of 5–10 MeV showed that the depth of penetration of electrons into alkali-halide crystals (in g/cm²) decreases on passing to a halide of higher atomic number with the alkali metal held constant.

When radiation interacts with dielectrics, energy is stored in them, expended in the formation of defects. A. V. Kuz’mina showed that the energy stored in crystals as a result of the action of γ-rays many times exceeds the magnitude of the stored energy in crystals with lower lattice energy. The established character of the dependence of stored energy on the chemical composition of crystals is well interpreted from the standpoint of the differing stability of radiation defects in crystals with unequal lattice energy, and is confirmed by the results of investigations of the density and stability of $F$-centers in crystals of the same compositions. Thus, S. K. Salo found that the density of $F$-centers at room temperature, and their stability, are higher in alkali-halide crystals with greater lattice energy. Owing to the greater stability of defects induced by radiation in crystals with a high value of lattice energy, the stored energy measured in them has a larger magnitude.

In works carried out under the direction of Docent I. Ya. Melik-Gaikazyan, the mechanism of the influence of defects on the radiation sensitivity of ionic crystals with respect to their electrical and optical properties has been investigated in considerable detail. The defectiveness of crystals was varied by introducing divalent impurities. Using a large number of systems as examples, it was shown that the dependence of the density of $F$-centers on impurity concentration in X-irradiated crystals is represented by curves with a maximum. The physical cause of these strange, at first glance, dependences was successfully explained, on the basis of ionic and electron-hole concepts, as a result of comprehensive studies of concentra-

tional dependences of electrical conductivity, spectra of activator absorption, microhardness, and the crystal-lattice parameter. The data obtained are of practical interest from the standpoint of the possible use of alkali-halide crystals (with additives) in radiation dosimeters and crystal counters.

Crystalline defects affect not only radiation resistance, but also many other properties of solids.

In work carried out in the laboratory of ED&P and directed by Professor P. A. Savintsev, the influence of structural defects on contact melting and on the thermal properties of crystals has been investigated. Contact melting is one of the interesting phenomena that arise upon contact between solids and consists in the fact that, when dissimilar crystals come into contact, their melting temperature (in the contact zone) becomes considerably lower than the melting temperature of the most fusible component of this system. The study of this phenomenon in the USSR was first begun in the 1940s at the Tomsk Polytechnic Institute by D. D. Saratovkin and was then continued on a broader experimental basis by P. A. Savintsev.

Work of recent years carried out at TPI has established the significant role of crystalline defects in the development of contact-melting processes. Thus, microscopic investigations of the contact-melting zone showed the mutual penetration of atoms of the components along defects in the structure of the crystals, including along grain boundaries, blocks, and especially along dislocations; this was more clearly traced in the example of irradiated objects, in which the defectiveness had been increased by radiation. It should be noted that contact melting has already found application in science and technology. Thus, for example, it is widely used in the pharmaceutical industry to obtain low-melting medicinal systems and mixtures, and is also beginning to be used in engineering to obtain fused contacts: metal—metal and metal—semiconductor.

In recent years, defects in crystals have increasingly begun to attract the attention not only of physicists, but also of chemists. Thus, for example, it is becoming clear that in solid-state chemistry crystalline defects also play a significant role. In this connection it is sufficient to mention, for example, the phenomena of catalysis on semiconductors, in which impurity defects create not only purely physical semiconductor properties, but also determine the active course of chemical-catalysis processes. But this is far from the only example. It turns out that crystalline defects also have a noticeable effect on other chemical processes, including processes of thermal decomposition, as was clearly shown in work carried out at TPI under the direction of Professor V. V. Boldyrev.

In these works, the influence on the rate of thermal decomposition of ionic crystals of a very wide variety of defects was studied in detail, such as: macrocracks, growth figures, whiskers, dislocations, foreign impurities, ionic and electronic defects, as well as changes in the crystal habit. It was established that the listed crystalline defects affect the thermal decomposition of a solid differently, depending on the type of reaction to which the decomposition process under consideration belongs—namely, whether it occurs through an electronic transition from anion to cation, or whether decomposition takes place as a result of the rupture of bonds within the cationic and anionic constituents of the lattice. It turns out that in the first case all of the above-listed defects noticeably affect the rate of thermal decomposition.

In the second case, however, this influence is of a more complex nature and, under certain conditions of the reaction, may be altogether absent.

In the works of V. V. Boldyrev, other interesting and important details of the influence of defects on thermal decomposition, as well as on the radiation-chemical stability of solids, have also been studied and revealed. Boldyrev’s investigations were awarded the All-Union D. I. Mendeleev Prize.

Another line of work in the physics and physical chemistry of the solid state at Tomsk Polytechnic Institute is connected with the study of the luminescence of crystals under the action of an electric field (electroluminescence) and under the influence of chemically active gases and flames (candoluminescence). The work is supervised by Prof. V. A. Sokolov.

As a result of investigations on electroluminescence carried out by V. L. Rabotkin, the strong influence of the properties of the dielectric used in the electroluminescent cell on the character of the electroluminescence of crystals in alternating and constant fields was demonstrated; the role of transition metals used in the electroluminophor as activators and coactivators was established, which made it possible to synthesize a number of new electroluminophors.

Investigations on candoluminescence (V. A. Sokolov and A. N. Gorban) led not only to a completely clear solution of a previously confused problem, but also laid the foundation for the development of a new branch of the theory of solid-state luminescence—the theory of radical-recombination luminescence of crystallophosphors—closely linking it with an important area of modern physicochemical electronic theory of catalysis on semiconductors (the works of Prof. F. F. Vol’kenshtein).

Such, in brief, are the scientific results of the work of the problem laboratory of EDiP in solid-state physics.

During the existence of the problem laboratory, i.e., since 1957, its staff members and postgraduate students have prepared and defended 5 doctoral and 25 candidate dissertations. The laboratory’s printed output to date comprises 16 published books and monographs and about 400 articles, published chiefly in the central scientific periodical press.

It should be noted that the EDiP problem laboratory participates rather actively in organizing and carrying out the educational process as well. The forms of this participation vary, but the main one is the broad involvement of students in research work and in the completion of course and diploma projects. Thus, 100–150 students work in the laboratory every year, half of whom complete diploma projects.

The laboratory has completed 18 economic-contract topics (within the laboratory’s subject area) and has received more than 30 certificates of registration for author’s certificates. The laboratory staff have delivered more than 200 reports at scientific conferences. Moreover, the laboratory is not only a participant in such conferences, but in a number of cases their initiator and organizer. Thus, in 1962, on the initiative of the problem laboratory, a scientific conference on the topic “The Effect of Radiation on the Properties of Solid Materials” was held at Tomsk Polytechnic Institute. At first the conference was conceived as a local one, intended for the exchange of our own experience in connection with the task set in the laboratory of studying the radiation resistance of insulators and semiconductors. However, in view of the great interest shown in this conference by ...

of other higher educational institutions, it spontaneously grew into an inter-institutional conference, with the participation of representatives of higher educational institutions and research establishments of Tomsk, Irkutsk, Novosibirsk, Moscow, and Tbilisi. The conference proceeded vividly and interestingly, at a high scientific level. On the basis of the materials of this conference, the West Siberian Council for the Coordination and Planning of Research Work of the Ministry of Higher and Secondary Specialized Education of the RSFSR published an inter-institutional thematic collection of scientific papers.

In February 1963, on the initiative and with the active participation of the staff of the Problem Laboratory of Electronics, Dielectrics, and Semiconductors at Tomsk Polytechnic Institute, an All-Union inter-institutional conference on the physics of breakdown in dielectrics and semiconductors was organized and held. In essence, it turned into a celebration for the problem laboratory, for the institute, and for Tomsk as a whole, to which numerous representatives of various higher educational institutions and research institutes of the country came. On the presidium of the conference one could see well-known scientists working in this field, who were direct students of the founder of the doctrine of dielectrics and semiconductors in the Soviet Union, Academician A. F. Ioffe: Professors B. M. Gokhberg, V. I. Granovsky, I. S. Stekolnikov, V. T. Renne, O. M. Todes, and others.

The total number of conference participants was about 500. In all, 164 reports were presented and discussed (of these, 40 reports were delivered by staff members of our problem laboratory).

All this indicates that the work of the scientists of Tomsk Polytechnic Institute in solid-state physics is arousing considerable interest and is winning ever closer attention and support from the broad scientific community of our country. The work of Tomsk scientists in solid-state physics is also followed with interest abroad. In noting all this, we must above all gratefully remember the founder of the Tomsk school of solid-state physics—Vladimir Dmitrievich Kuznetsov.