Evolution of the dielectric and acoustic parameters of chromium-doped SBN single crystals with variations in temperature

The temperature dependences of the dielectric characteristics of Sr_0.61Ba_0.39Nb_{2 − x} O₆: Cr _x ³⁺ single crystals with x = 0.0, 0.005, and 0.010 are investigated in the low-frequency and infrared ranges. It is revealed that the behavior of the dielectric response exhibits specific features in the vicinity of the transition from the ferroelectric phase to the paraelectric phase and in the low-temperature range. The measurements are performed along the [001] (polar axis) and [100] directions. The temperature dependences of the relative sound velocity and the attenuation of elastic waves are also studied, and the temperature ranges of the anomalous behavior of these parameters are determined. The specific features revealed in the behavior of the dielectric and acoustic properties are considered from the viewpoint of the structural transformations occurring in the SBN system upon doping with a chromium impurity. Original Russian Text ? A.S. Pilipenko, A.I. Burkhanov, L.I. Ivleva, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 543–546.     

Effect of Ga and As sublayers on the structures and properties of Ni-GaAs contacts

Studies were made of heat-treated Ni-GaAs contacts, at which, prior to the electrochemical deposition of nickel, thin layers of gallium or arsenic were deposited. The physicochemical reactions at the interfaces were investigated, as well as the electrophysical characteristics of the diodes, the morphology of the metallic coatings, and the mechanical stresses. The phase composition of the contacts and the height of the barrier are seen to be practically independent of the introduction of excess Ga or As, whereas the thermal stability of the electrical parameters of the diodes varies considerably. This difference is associated with the effect of the Ga and As sublayers on the magnitude of the mechanical stresses arising at the metal-semiconductor interface.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 46–51, February, 1987.     

Luminescent and laser properties of Yb–Er:GdCa<Subscript>4</Subscript>O(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>: a new crystal for eye-safe 1.5-μm lasers

We present for the first time 1.5-m laser emission in Yb–Er:GdCa₄O(BO₃)₃ (GdCOB). The crystals were grown by the Czochralski method from platinum crucibles. Spectroscopic and laser tests of the crystals are described. A continuous-wave output power of 80 mW was achieved in a monolithic microchip cavity under laser-diode pumping. PACS 42.55.Xi; 42.70.Hj     

Synthesis of hydroxy derivatives from adamantanecarboxylic acids in the system MnO<Subscript>2</Subscript>–H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

A convenient procedure has been developed for the synthesis of mono- and dihydric cage alcohols from adamantanecarboxylic acids and their esters using the MnO₂–H₂SO₄ system. The reaction at elevated temperature involved both decarboxylation and decarbonylation of the initial acid or ester.     

Antioxidant activity of 2-methyl-1,3-benzoxazol-6-ol

Antioxidant effect of 2-methyl-1,3-benzoxazol-6-ol in radical chain oxidation of organic compounds with molecular oxygen was studied. Antiradical activity in the reaction with stable diphenylpicrylhydrazyl radical was examined by photocolorimetry. The kinetic parameters of the reaction of 2-methyl-1,3-benzoxazol-6-ol with peroxy radicals of different natures were determined by volumetric and chemiluminescence methods. A relation was found between the antioxidant activity and electronic structure parameters calculated by quantum-chemical methods. Factors responsible for differences in chemiluminescence in the oxidation of organic substances with different polarities in the presence of the title compound were analyzed.     

Reactions of 2-hydroxymethylphenols with Lawesson's reagent

On interacting 2-hydroxymethylphenols and the Lawesson's reagent 2-(4-methoxyphenyl)-4H-1,3,2-benzoxathiaphosphinine-2-sulfides were obtained. The formation of highly reactive o-quinone methides as intermediates is proposed.     

Passive Q-switching at 1.54 μm of an Er–Yb: GdCa4O(BO3)3 laser with a Co2+: MgAl2O4 saturable absorber

We report, for the first time to our knowledge, efficient passive Q-switching of the 1.54-μm laser transition in an Er–Yb-doped crystalline medium. The laser configuration is a compact microchip design that is suitable for a range of practical applications such as range finding and lidar. The slope efficiency of 11.6%, pulse duration of 5–6 ns and average output power of 88 mW are all comparable with standard Er–Yb:glass lasers.     

Effect of gamma irradiation on the dielectric response of a Sr0.75Ba0.25Nb2O6 relaxor single crystal

The effect of gamma irradiation from a ⁶⁰Co source at a dose D = 4.75 × 10⁴ R on the dielectric properties of a Sr_0.75Ba_0.25Nb₂O₆ (SBN-75) single crystal with a smeared phase transition is investigated in the low-and infralow-frequency ranges. The behavior of the dielectric response is compared with the behavior of the depolarization currents induced in unirradiated and irradiated samples of the Sr_0.75Ba_0.25Nb₂O₆ compound. The observed changes in the electrical properties of the Sr_0.75Ba_0.25Nb₂O₆ single crystal in the temperature range of the smeared phase transition are associated with the stabilization of the ferroelectric phase of the material in an internal bias field generated by radiation-induced defects.