Reports of the Academy of Sciences of the USSR
1969. Vol. 189, No. 5

UDC 539.89

PHYSICS

O. B. Yakusheva, V. V. Yakushev, A. N. Dremin

DESTRUCTION OF COLOR CENTERS IN NaCl SINGLE CRYSTALS DURING SHOCK COMPRESSION

(Presented by Academician V. N. Kondrat’ev on 12 V 1969)

Recently the possibility of the generation of point defects in single crystals by a shock-wave front has been pointed out repeatedly ($^{1}$). This assertion is usually associated with the strong plastic deformations that a substance undergoes in a shock transition, since the latter lead to the creation of positive and negative ionic vacancies, as well as their simplest aggregates ($^{2,3}$).

In specimens of MgO preserved after shock compression it proved possible to detect $F$ centers ($^{4}$), and also to observe a noticeable increase in the bleaching rate under irradiation with white light of preserved NaCl crystals containing $F$ centers ($^{5}$).

However, preserved specimens, along with the action of the shock-wave front, are subjected to intense plastic deformations in the rarefaction wave; therefore the question of experimental confirmation of defect generation by the shock-wave front remains open.

Since the bleaching rate of colored crystals is proportional to the concentration of traps present in them—for example, vacancy aggregates that absorb optically excited electrons of $F$ centers—it is of interest to observe directly the absorptive capacity of single crystals containing $F$ centers during shock compression.

Color changes in NaCl single crystals colored at a Co$^{60}$ source with a dose of 0.75 Mrad and subjected to shock compression along the [100] axis were recorded by the light-reflection method ($^{6}$) on an SFR-2 instrument using DS-2 color photographic film, which, in order to increase its photosensitivity, was treated by the method of the Central Scientific-Research Institute of Geodesy, Aerial Photography, and Cartography ($^{7}$). The crystal was irradiated by an explosive argon light source through a Plexiglas filter.

The scheme of the experimental setup and the photographic chronogram of the process of passage of the shock wave through the crystal are given in Fig. 1 (see insert to p. 975). It follows from the experiments that irradiation of the crystal by the intense light of the argon source for $\sim 13\ \mu$sec does not lead to appreciable bleaching, which, however, occurs when the shock wave enters the specimen in times less than 0.5 $\mu$sec. We note that when the shock-wave front propagates through the auxiliary colorless crystal 3, no color changes are recorded.

Bleaching of the crystals during shock compression was observed for pressures $p = 30$ and 180 kbar. If for $p > 60$ kbar this phenomenon can be explained by a shift of the absorption band of $F$ centers under compression ($^{8}$), then bleaching at $p \approx 30$ kbar must be associated with the appearance of a large number of electron traps in the shock-wave front, since thermal bleaching under these conditions is excluded ($^{9}$). (According to

(10); at \(p \approx 30\) kbar the temperature of the NaCl crystal in the shock wave increases by \(20^\circ\).)

Branch of the Institute of Chemical Physics
Academy of Sciences of the USSR
Chernogolovka, Moscow Region

Received
28 IV 1969

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