High sensitive and ultrafast UV photodetector based on ZrO_2 single crystals

The fast-response ultraviolet (UV) photoelectric effect in ZrO2 single crystals with interdigitated electrodes has been investigated experimentally at room temperature. The photovoltage of ZrO2 single crystals exhibits a linear dependence on applied bias and light power density. The photocurrent responsivity to the UV light with a wavelength of 253.65 nm is 9.8 mA/W. For the photovoltaic pulse, a rise time of 501 ps and a full width at half maximum of 1.5 ns have been obtained, when the ZrO2 single crystal ...     

Energy spectrum and optical absorption in p-CdGeAs2

In the Kein four-band model, taking account of interaction with excited bands, the energy spectrum and effective masses of electrons and holes in CdGeAs₂ are calculated. The polarizational dependence of the optical absorption spectrum is investigated for transitions between bands of light and heavy holes. The results are compared with experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 68–72, January, 1982.     

Temperature effects on positron annihilation in metallic single crystals

A Ge(Li) spectrometer was used to measure the temperature-dependence of the intensity of gamma rays resulting from positron annihilation in single crystals of Pb, Sn, Ge and Cu. In contrast to recent angular distribution results, no significant temperature effects were observed.     

Electronic processes in oxide glassy semiconductors and thin-film structures based on them

The physical nature of electronic processes in oxide glassy semiconductors (OGS) based on V₂O₅ is discussed on the basis of the theory of the small radius polaron (SRP). The most important parameters of the process of charge transfer by polarons are determined from an analysis of the temperature dependence of the static conductivity by mathematical modeling employing general theoretical expressions. A model of coupled SRP, presuming that they are localized by the Coulomb field of the charged defect centers, is proposed for describing the complex of data on the effects of a strong electric field and dielectric relaxation. On the basis of the model expressions describing the dependence of the current density and dielectric constant on the dc electric field strength and also a relation determining the dielectric relaxation time for the given model are obtained. The results of studies of the electric properties of OGS, modified by additions of a second transition-metal oxide, are discussed also.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 18–33, June, 1987.     

Surface effects and defect structures in ferroelectric liquid crystals

Summary The influence of boundaries on the smectic structure dielectric properties and polarization reversal processes in thin films of ferroelectric liquid crystals are discussed. Work presented at the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30-October 2, 1987.     

Rational approximant pentagonal crystals based on icosa-hedral structures

The generation of periodic quasicrystals by the projection method is considered. The effects of the simulteneous distortion of the projected icosahedron and 6D hyperlattice are presented.     

Electroluminescence in CuGaSe2 single crystals

Electroluminescence has been observed in p-type CuGaSe₂ single crystals. At room temperature these crystals exhibit a resistivity of about 10^?2 Ω cm. The electrominescence has been obtained by minority carrier injection from an indium electrode. Two peaks have been identified in the emission spectrum whose energies are 1.53 and 1.59 eV, respectively. These peaks could be caused by the recombination of injected minority carriers in acceptor centers which are localized in the forbidden gap near the valence band.     

Domain structures in orthorhombic KNbO3 and characterisation of single domain crystals

Domain configurations in large KNbO₃ single crystals grown by a top seeded flux growth technique are studied by optical methods and etching techniques. The orientation of observed domain walls is consistent with the principles of mechanical compatibility and electrical neutrality. Experimental evidence for the existence of a new type of ferroelectric domain wall (S-wall) is presented. Miller indices of such walls are irrational and depend on spontaneous strain tensor coefficients. The preparation of large single domain crystals (up to 1/3 cm³) is described. Assessment of crystal perfection by x-ray topographic and interference methods reveals a very small mosaic spread (one minute of arc) and a good optical homogeneity.     

Recombination radiation in p-ZnSnP2 single crystals

We have carried out complex investigations into the recombination radiation of p-ZnSnP₂ single crystals produced by methods involving recrystallization from nonstoichiometric melts with cooling at a controlled rate (type-I crystals) and under steady-state conditions (type-II crystals). We discuss the effect of crystal-growth conditions on the spectral contour and the position of the band maxima for recombination radiation. Type-II crystals exhibit edge exhibition and it is demonstrated that the shift of the long-wave bands in type-I crystals is controlled by the rate of cooling. The nature of the observed radiation transitions is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 43–48, April, 1986.     

NMR spin echoes and quadrupole effects in nickel single crystals

NMR spin echo measurements of naturally abundant⁶¹Ni have been performed with Néel-type nickel single crystals at 4.2 K. The NMR excitation condition could properly be chosen in order to get signals either from nuclei situated within magnetic domains or within domain walls. In both cases a quadrupole splitting of the NMR line could be observed. By applying an external magnetic field, the direction of the domain magnetization could be varied with respect to the fcc crystal lattice. From the variation of the quadrupole splitting with the crystallographic direction, the tensor of the electric field gradient (EFG) has been derived. The quadrupole splittings and the corresponding field gradients in the principal axis system of the EFG are: Δv_Q kHz, Δv_Q kHz, Δv_Q kHz, V_<111>=(6.6±0.5)·10¹⁸ V/m², V_<110>=4.6±0.5)·10¹⁸ V/m², V_<112>=(2.0±0.5)·10¹⁸ V/m².