High pressure effects in severe plastic deformation

The analysis is made of effect and physical mechanisms of the influence of pressure on metal materials that are in the state of plastic flow, as well as on characteristics of materials undergone severe plastic deformation under pressure

Influence of preliminary hydrostatic pressure treatment on the electrical resistance and structure of amorphous Co₆₇Cr₇Fe₄Si₈B₁₄ alloy

The effect of preliminary pressure treatment (PT) on peculiarities of changes in electrical resistance R and structure of the amorphous Co₆₇Cr₇Fe₄Si₈B₁₄ alloy during a constantrate heating to temperatures under the crystallization onset temperature has been studied using the resistance measurement and X-ray diffraction (XRD) methods. Preliminary PT has been done at 300 K (P = 1 GPa) in the repetitive static mode for different number N of loading cycles (N = 1, 3, 5).The XRD data show that the amorphous state of the studied alloy is conserved but its fine structure has changed after PT, as observed by variation of halo parameters. It has been found that after PT with an increase in the number N of loading cycles, the ordering of the original amorphous structure is enhanced, while after heating from 828 to 843 K, the disordering growth is enhanced. Anomalies of R (a minimum at 497 K and a sharp rise in the range of 800–843 K) observed in the dependence R(T) of the original amorphous alloy are present after the PT too. They seem to be due to structural phase transitions of amorphous alloy during heating.Методами резистометрии и рентгеноструктурного анализа (РСА) изучено влияние предварительной обработки давлением (ОД) на особенности изменения электрического сопротивления R и структуры аморфного сплава Co₆₇Cr₇Fe₄Si₈B₁₄ при нагреве с постоянной скоростью до температур не выше температуры начала кристаллизации. ОД проведено при комнатной температуре в повторно-статическом режиме с разным числом N циклов обработки (N = 1, 3, 5) при давлении P = 1 GPa. По данным РСА, после ОД аморфное состояние изучаемого сплава сохраняется, но тонкая структура гало изменяется. Показано, что с ростом N циклов ОД растет упорядочение, а при нагреве в интервале 828–843 K – разупорядочение исходной аморфной структуры сплава. Аномалии R (минимум при 497 K и резкий рост в окрестности 800–843 K), наблюдаемые на зависимости R(T) исходного аморфного сплава, после ОД сохраняются и связаны, по-видимому, со структурными фазовыми переходами в процессе нагревания сплава.Методами резістометрії та рентгеноструктурного аналізу (РСА) вивчено вплив попередньої обробки тиском (ОТ) на особливості зміни електричного опору R та структуру аморфного сплаву при нагріванні з постійною швидкістю до температур, які не перевищують температуру початку кристалізації. ОТ проведено при кімнатнiй температурі у повторно-статичному режимі з різним числом N циклів навантаження (N = 1, 3, 5) при тиску Р = 1 GPa. За даними РСА, після ОТ аморфний стан сплаву, що вивчається, зберігається, але тонка структура гало змінюється. Показано, що зі зростанням N циклів ОТ зростає упорядкування, а при нагріванні в интервалі 828–843 K – розупорядкування вихідної структури сплаву. Аномалиії R (мінімум при 497 K та різке зростання в межах 800–843 K), які спостерігаються на залежності R(T) вихідного аморфного сплаву, після ОТ зберігаються та пов′язані, напевно, зі структурними фазовими перетвореннями аморфного сплаву у процесі нагрівання сплаву.

The internal friction and phase transition of solid oxygen

We report an experimental study of the low frequency internal friction (LTIF) in solid oxygen in temperature range 7–52 K. Comparison of the temperature dependence of IF with data of x-ray diffraction and other thermodynamic and elastic properties, shows that anomalies of temperature dependence of the internal friction are resulted from phase transitions in solid oxygen

Comparison of pressure, magnetic field and excess manganese effects on transport properties of film and bulk ceramic La–Ca manganites

The pressure, magnetic field and excess manganese effects on transport and magnetoresistance effect (MRE) have been studied in both the epitaxial films and bulk ceramics of manganites (La₀.₇Ca₀.₃)₁₋xMn₁₊xO₃₋y (x = 0–0.2). A comparison of electrical behavior in both kinds of samples of similar composition at hydrostatic pressures of up to 1.8 GPa and in a magnetic fields of up to 8 kOe has been performed. The pressure and magnetic field effects are shown to increase with increasing manganese content. Experimental data show that the pressure and magnetic field effects on temperatures of both metal–insulator transition (TMD) and MRE peak (TMR) are considerably stronger in the films than in ceramics. The hydrostatic pressure increases TMD and TMR. Magnetoresistance effect for both types of samples was shown to be favored by the pressure and magnetic field in an opposite way. A direct correlation is established between TMD and conductivity bandwidth as well as between MRE and concentration of charge carriers at applied pressure. The differences in the values of pressure effect on resistance, MRE and TMD temperature in the films and ceramics are connected with both granular structure of ceramics and the oxygen nonstoichiometry in ceramic and film samples of the same content as well as with the film strain induced by lattice mismatch between the film and the substrate. The origin of pressure–magnetic field effects is analyzed in the framework of double exchange interaction and small polaron hopping, and variable range hopping models

Unconventional ferromagnetism and transport properties of (In,Mn)Sb dilute magnetic semiconductor

Narrow-gap higher mobility semiconducting alloys In_{1-x}Mn_{x}Sb were synthesized in polycrystalline form and their magnetic and transport properties have been investigated. Ferromagnetic response in In_{0.98}Mn_{0.02}Sb was detected by the observation of clear hysteresis loops up to room temperature in direct magnetization measurements. An unconventional (reentrant) magnetization versus temperature behavior has been found. We explained the observed peculiarities within the frameworks of recent models which suggest that a strong temperature dependence of the carrier density is a crucial parameter determining carrier-mediated ferromagnetism of (III,Mn)V semiconductors. The correlation between magnetic states and transport properties of the sample has been discussed. The contact spectroscopy method is used to investigate a band structure of (InMn)Sb near the Fermi level. Measurements of the degree of charge current spin polarization have been carried out using the point contact Andreev reflection (AR) spectroscopy. The AR data are analyzed by introducing a quasiparticle spectrum broadening, which is likely to be related to magnetic scattering in the contact. The AR spectroscopy data argued that at low temperature the sample is decomposed on metallic ferromagnetic clusters with relatively high spin polarization of charge carriers (up to 65% at 4.2K) within a cluster.Comment: 19 pages, 9 figures, 1 tabl

Influence of UV-radiation on structure and properties of diamond-like a-C:N films

Study results on effect of a low power (up to 1 W/cm²) UV and visible radiation on the structure and properties of diamond-like carbon nitride (α-C:N) films during their growth have been presented. The UV irradiation of the growing film surface has been found to be effective for the graphite phase etching and to result in an improved structure ordering of the film and enhanced quality thereof.Представлены результаты исследования воздействия УФ- и видимого излучения невысокой мощности (до 1 Вт/см² на структуру и свойства алмазоподобных пленок нитрида углерода α-C:N в процессе их роста. Обнаружено, что УФ-облучение ростовой поверхности пленок эффективно для травления графитной фазы, ведет к росту структурной упорядоченности пленок и улучшает их качество.Представлено результати досліджєння впливу УФ- i видимого випромінювання невисокої потужності (до 1 Вт/см²) на структуру і властивості алмазоподібних плівок нітриду вуглецю α-C:N у процесі їхнього росту. Виявлено, що УФ-опромінення ростової поверхні плівок ефективно для травлення графітної фази, веде до росту структурної упорядкованості плівок і поліпшує їхню якість

Upper critical field of Me-Y-Ba-Cu-O (Me=Zr, Hf)

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