Quasi-phase-matched optical activity effect in “gyroelectric” crystals and its applications

“Quasi-phase matching” is first introduced to the optical activity (OA) effect and a wave coupling theory for the quasi-phase-matched (QPM) OA effect in periodically poled “gyroelectric” crystals is developed. The OA effect is observed clearly even though the propagating direction of light deviates far from the optical axis in the QPM crystal with both optical activity and natural birefringence. The QPM OA effect provides a special way to determine the gyration coefficients that cannot be observed by the normal OA effect, and it provides a principle for building optical filters without external field.     

Spin-dependent transport in α-MnS single crystals

The electrical resistivity of single crystal α-MnS in crystallographic directions [111] and [100] was found to be anisotropic in the temperature interval 77–300 K. The change in activation energy below the Néel temperature was determined. Magnetoresistance was revealed, and reversal of its sign in the (111) plane above the Néel point was found. The experimental data are analyzed in terms of the s-d model, with the manganese ion holes interacting with localized spins assumed to be free carriers.     

Generation of an ultrashort optical pulse by four-wave Raman mixing in deuterium cooled at 77 K

When a 100-fs Ti:sapphire laser is focused into molecular deuterium cooled at 77 K, rotational stimulated Raman emission is generated based on four-wave Raman mixing. By phase locking the emission lines, the laser pulsewidth was reduced to 40 fs, when a nearly transform-limited pulse was utilized as a fundamental laser. The pulsewidth was further reduced to 20 fs, when a positively chirped pulse was employed. Computer simulation suggests that the Raman emission is strongly chirped and a train of pulses with lower intensities are formed when a chirp pulse is used as a fundamental laser. PACS 42.65.Dr; 42.55.Ye; 42.50-p     

On the pyroelectricity of DKDP single crystals and PZT-40 ceramics at 1.5–30 K

By analyzing experimental data, the lowest modes that are responsible for pyroelectricity in DKDP single crystals (87.3 and 201.6 cm^?1) and in PZT-40 ferroelectric ceramics (20.7, 54.75, and 171.3 cm^?1) are determined. A set of physical mechanisms that occur in real polar dielectrics that are piroelectrically active in the temperature range 0–30 K is discussed; and methods of their identification, separation, and determination of quantitative characteristics for each component of spontaneous polarization are shown.     

Deformation autowaves in nitrogen-doped γ-Fe single crystals

Experimental data on the evolution of macrodeformation fields of single-crystal samples of austenitic chromium-nickel steel with a superequilibrium nitrogen content under tension are analyzed on the basis of a model of autowave plastic flow. The conditions for the appearance and observation of different types of autowave deformation structures are established; such structures include a solitary front, a traveling autowave, and a stationary dissipative structure and are determined by the crystal-geometry of deformation and by the nitrogen concentration in the material. It is shown that a one-to-one correspondence exists between the type of deformation autowave and the stage of the plastic flow curve of the material. Zh. Tekh. Fiz. 69, 56–62 (October 1999)     

Calorimetric study of N-isopropyl carbazole single crystals in the range 125–240 K

The specific heat (C_p) of N-isopropylcarbazole crystal has been measured in the temperature range 125–240 K by differential scanning calorimetry. A sharp endotherm was found at 137 K (ΔH = 123 cal·mol⁻¹), confirming the occurrence of a first order phase transition, recently reported in literature. Another interesting finding is a ∼ 10% rise of C_p between 170 and 200 K which might be associated with another (non-first order) phase transition.     

Effect of low-temperature compression on the parameters of the phase transition at 250–260 K in C60 single crystals

A thermodynamic transition in C₆₀ crystals, subjected beforehand to uniaxial compression at various temperatures and to thermal action, was investigated by differential scanning calorimetry. It was established that compression of the crystal at temperatures below the phase transition has a much smaller effect on the transition itself than a similar or even much weaker action at a temperature above the phase transition. A “quenching” effect was also found. This effect is probably due to the orientational order of individual fullerene molecules. A correlation was established between the magnitude of the effect and the preliminary deformation of C₆₀ crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 550–553 (March 1999)     

Small-inelastic-strain rate spectrum of C60 single crystals near the phase transition at 250–260 K

The temperature spectrum of small-inelastic-strain rates in a vapor-phase-grown C₆₀ single crystal has been measured within the 200–290 K interval with a high-precision strain-rate meter based on a laser interferometer. The spectrum exhibits a strong peak in the region of the phase transition at 250–260 K and a slight strain acceleration at ∼240 K, which correlates well with the calorimetric curve. The first maximum is associated with strain that developes more easily in an fcc than in a primitive cubic lattice, and the second, to the effect on the strain rate of annealing of the defects created with fast crystal heating. Fiz. Tverd. Tela (St. Petersburg) 41, 1115–1118 (June 1999)     

Inelastic deformation of C60 single crystals in the temperature range 80–300 K

The rate spectrum of small inelastic strains of the C₆₀ single crystal in the temperature range 80–300 K has been obtained with a precision laser interferometer. It is revealed that the spectrum exhibits two large peaks in the glass formation (90–100 K) and phase transition (250–260 K) ranges. A small strain acceleration is also observed at ～220 and 240 K. The first two maxima are attributed to the changes in strain resistance upon transitions, and the strain acceleration at 220 and 240 K is associated with the annealing of the defects formed upon rapid cooling of the crystal. It is demonstrated that the peak at 250–260 K broadens with an increase in the stress. The spectrum of strain rates is compared with the calorimetric curve for the same single crystal.     

Depolarization ofμ + muons in GaAs single crystals

ASR study has been carried out on high resistivity single crystal gallium arsenide (GaAs). Three characteristic states involving the ⁺ muon (Mu^*, Mu, ⁺ were shown to exist in a binary semiconductor, similar to the case of elemental semiconductors.     

Afterglow in bulk AlN single crystals under β-irradiation

Regularities of afterglow at room temperature and of thermoluminescence at further heating up to 673 K have been studied in bulk aluminum nitride single crystals. It has been established that after exposure to β-irradiation luminescence decay at RT may be described by superposition of two exponential components: fast (59 s) and slow (606 s) ones, caused by defects of the anion crystal sublattice O_N- and V_N-centers, respectively. The afterglow spectrum is shown to be characterized by the 3.43 eV band with FWHM=0.61 eV that dominates also in the thermoluminescence under study. From analysis of the TL curves in terms of the general order formalism it has been concluded that variation of the activation energy observed within the 0.46–0.85 eV range with increasing storage of the samples from 5 min to 3 days may be caused by energy distribution of traps on the basis of oxygen-related centers. For the first time the compensation effect has been found, and phenomenologically interpreted for the TL processes of the AlN single crystals. Isokinetic temperature has been estimated within the framework of empiric and non-empiric relations.     

Piezoelectric properties of tetragonal single-domain Mn-doped NBT-6 %BT single crystals

We report a study of properties of Mn-doped NBT-6 %BT single crystals. We show that tetragonal single-domain states can be stabilized by poling along a [001] direction. For carefully prepared crystals, the piezoelectric coefficient \(d_{33}\) can reach 570 pC/N. When poled along non-polar directions, the crystals exhibit ferroelectric domain structures consistent with tetragonal micron-sized domains, as revealed by optical observation and Raman spectroscopy. The multidomain crystals have lower \(d_{33}\) values, 225 and 130 pC/N for [011] and [111]-oriented crystals, respectively. This trend is commented on from a domain-engineering perspective.     

Self-diffusion in α-Fe2O3 natural single crystals

Measurements of¹⁸O self-diffusion in hematite (Fe₂O₃) natural single crystals have been carried out as a function of temperature at constant partial pressure a_{O 2}=6.5·10^?2 in the temperature range 890 to 1227 °C. The a_{O 2} dependence of the oxygen self-diffusion coefficient at fixed temperature T=1150 °C has also been deduced in the a_{O 2} range 4.5·10^?4 - 6.5·10^?1. The concentration profiles were established by secondary-ion mass spectrometry; several profiles exhibit curvatures or long tails; volume diffusion coefficients were computed from the first part of the profiles using a solution taking into account the evaporation and the exchange at the surface. The results are well described by $$D_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 2.7 \cdot 10^8 a_{O_2 }^{ - 0.26} \exp \left( { - \frac{{542\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ From fitting a grain boundary diffusion solution to the profile tails, the oxygen self-diffusion coefficient in sub-boundaries has been deduced. They are well described by $$D''_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 3.2 \cdot 10^{25} a_{O_2 }^{ - 0.4} \exp \left( { - \frac{{911\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ Experiments performed introducing simultaneously¹⁸O and⁵⁷Fe provided comparative values of the self-diffusion coefficients in volume: iron is slower than oxygen in this system showing that the concentrations of atomic point defects in the iron sublattice are lower than the concentrations of atomic point defects in the oxygen sublattice. The iron self-diffusion values obtained at T>940 °C can be described by $$D_{Fe} \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 9.2 \cdot 10^{10} a_{O_2 }^{ - 0.56} \exp \left( { - \frac{{578\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ The exponent - 1/4 observed for the oxygen activity dependence of the oxygen self-diffusion in the bulk has been interpreted considering that singly charged oxygen vacancies V _O ^? are involved in the oxygen diffusion mechanism. Oxygen activity dependence of iron self-diffusion is not known accurately but the best agreement with the point defect population model is obtained considering that iron self-diffusion occurs both via neutral interstitals Fe _x ⁱ and charged ones.     

Laser emission of 2,2″-dimethylparaterphenyl at 77 K

Dye laser emission of 2,2-dimethylparaterphenyl at 77 K down to 208.5 nm is reported.     

Influence of the donor concentration on the decay kinetics of sensitized phosphorescence of 1,3,5-triphenylbenzene in toluene at 77 K

Dependence of the kinetics of sensitized phosphorescence (SP) of 1,3,5-triphenylbenzene (1,3,5-TPB) on the concentration of the energy donor – benzophenone (BP) – is studied in toluene at 77 K. An increase in the SP decay rate of 1,3,5-TPB with concentration is established. It is demonstrated that the reason for the increase in the decay rate is the increased radiative deactivation rate constant of triplet excitations caused by exchange interactions. The coefficient characterizing the exponential dependence of the radiative deactivation rate constant for triplet excitations of 1,3,5-TPB on the intermolecular distance in the donor-acceptor pair is determined.