Laser initiation of a mixture of PETN with NiC nanoparticles at elevated temperatures

The temperature dependence of the probability of the explosion of pentaerythritol tetranitrate (PETN) with an admixture of NiC particles (0.3 wt %) initiated by laser pulses (1064 nm, 20 ns) was studied over the temperature range 295–450 K. At 295–350 K, a weak temperature dependence was observed. The determining contribution to explosion initiation was made by the absorption of laser radiation by nanoparticles. The threshold of explosive decomposition at 295 K decreased by ∼40 times compared with samples free of NiC nanoparticles. Over the temperature range 400–450 K, the threshold of the explosive decomposition of samples containing NiC nanoparticles decreased with the activation energy ∼0.4 eV. A decrease in the threshold of explosive decomposition with a ∼0.4 eV activation energy over the temperature range 340–440 K was also observed for laser action on PETN samples not containing NiC. A hypothesis was suggested according to which the absorption of a light quantum caused the transfer of an electron from the valence band of the crystal to a level in the forbidden band with subsequent thermal positive ion dissociation to the carbocation and NO₃ radical.     

Charge-sensitive deep level transient spectroscopy of helium-ion-irradiated silicon, as-irradiated and after thermal annealing

Electrically active defects in the phosphor-doped single-crystal silicon, induced by helium-ion irradiation under thermal annealing, have been investigated. Isothermal charge-sensitive deep-level transient spectroscopy was employed to study the activation energy and capture cross-section of helium-induced defects in silicon samples. It was shown that the activation energy levels produced by helium-ion irradiation first increased with increasing annealing temperature, with the maximum value of the activation energy occurring at 873K, and reduced with further increase of the annealing temperature. The energy levels of defects in the samples annealed at 873 and 1073K are found to be located near the mid-forbidden energy gap level so that they can act as thermally stable carrier recombination centres.     

Grain Boundary Migration in Fe-3wt.%Si Alloys

The studies of three different laboratories on grain boundary migration in Fe-3wt.%Si alloys are presented. In all cases bicrystal techniques employing capillarity as driving force were used. [100] tilt boundaries were studied in the temperature range from 1223 K to 1373 K, and [110] tilt boundaries in the range from 1220 K to 1625 K. Proportionality between grain boundary velocity and driving force was confirmed. All data fulfil a linear relation between activation enthalpies and logarithms of the pre-exponential factors, corresponding to a compensation temperature of 1386 K where all boundaries theoretically should possess the same mobility. A considerably lower activation enthalpy was found in one case for an asymmetrical grain boundary compared to the symmetrical boundary of the same misorientation. High values of activation enthalpy of migration were found for special [100] boundaries compared to general ones although an opposite tendency was also observed for [100] boundaries.     

A comparative study of the solid-matrix phosphorescence of heterocyclic aromatic amines in glucose glasses as a function of temperature

Solid-matrix phosphorescence intensities and lifetimes were obtained for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-9H-pyrido[2,3-b]indole (AαC) as a function of temperature from room temperature to 93 K. The two solid matrices employed were glucose glasses prepared with crystalline glucose and a glucose melt, both with and without a heavy-atom salt, NaI. In general, the phosphorescence intensities and lifetimes of PhIP increased as the temperature was lowered. The intensity-to-lifetime ratios showed that the triplet state formation efficiency of PhIP changed as a function of temperature for glasses prepared without NaI. This illustrated that the phosphorescence intensity was a function of both triplet state formation efficiency and phosphorescence lifetime. For the glasses prepared with NaI, the triplet state formation efficiency of PhIP remained essentially constant with temperature. Thus, the phosphorescence intensity was only a function of phosphorescence lifetime. The phosphorescence intensity for AαC was essentially the same at room temperature and at 93 K in glasses prepared with 10% NaI. Thus, this heavy-atom salt/glucose system was able to achieve the maximum phosphorescence signal at room temperature. Using the phosphorescence lifetimes as a function of temperature, activation energies for the phosphors in the glasses were calculated. The phosphorescence lifetime data fit a biexponential equation and two activation energies were obtained. The lower activation energy was related to low-frequency vibrations in the glucose matrix, and the higher activation energy was related to β-relaxation processes that occur in glucose glasses.     

Microwave conductivity of K-TCNQ

Measurements of microwave conductivity of K-TCNQ in the temperature range 300–450 K are reported. K-TCNQ behaves as an extrinsic semiconductor with an activation energy of 0.26 eV below the spin-Peierls transition temperature of 396 K and 0.13 eV above the transition. A hystersis of about 1.5 K was observed. Carrier mobility appears to be reduced by a factor of 30 in the high temperature phase. A second type of crystal has been identified with room temperature conductivity two orders of magnitude higher than previously reported.     

Efficiency of laser initiation and absorption spectra of PETN

A comparative study of the efficiency of the laser initiation of PETN by the first and second harmonics (1060 and 530 nm) of a neodymium-doped phosphate glass laser was performed. A significant difference in the efficiency of PETN initiation by the different harmonics was revealed: as the initial temperature of the sample increased from 373 to 450 K, the threshold initiation fluence decreased from 3.0 to 0.5 J/cm²; at the same time, the second harmonic failed to initiate PETN even at a fluence of 10 J/cm². The absorption spectrum of PETN was found to have a weak absorption band with a maximum at λ _m = 1020 nm. It was assumed that the high efficiency of initiation by the first harmonic is associated with light absorption (photo-initiation) by this band     

Transport spectroscopy through dopant atom array in silicon junctionless nanowire transistors

We demonstrate electron transport spectroscopy through a dopant atom array in n-doped silicon junctionless nanowire transistors within a temperature range from 6 K to 250 K. Several current steps are observed at the initial stage of the transfer curves below 75 K, which result from the electron transport from Hubbard bands to one-dimensional conduction band. The current-off voltages in the transfer curves have a strikingly positive shift below 20 K and a negative shift above 20 K due to the electrostatic screening induced by the ionized dopant atoms. There exists the minimum electron mobility at a critical temperature of 20 K, resulting from the interplay between thermal activation and impurity scattering. Furthermore, electron transport behaviors change from hopping conductance to thermal activation conductance at the temperature of 30 K.     

无序GaInP光致发光谱的温度依赖关系

研究了无序ＧａＩｎＰ样品的温度依赖关系，大低温ＰＬ谱中，谱线呈单峰结构。随着温度从１５Ｋ升高到２５０Ｋ，说地宽从１６ｍｅＶ增大到３１ｍｅＶ，并且发生红移，同时强度减小两个数数量级。     

溶胶-凝胶法制备的纳米TiO2结构相变及晶体生长动力学

讨论了采用溶胶-凝胶法经由先驱物钛酸四异丙脂水解而制备的纳米TiO₂粉末的 结构相变 ，并讨论了该纳米粉末的生长动力学机理.结果表明，水解pH值为0.9，当高压釜热处理温度 ＜503K时，粉末晶粒度增长较为缓慢，而当热处理温度＞503K时，粉末粒度明显长大.应用 相变理论计算出了纳米TiO₂颗粒的两阶段的生长激活能，分别是18.5kJ/mol和5 9.7kJ/mol .XRD物相分析表明，高压釜热处理温度达到503K时，样品就开始发生锐钛矿到金红石相的结 构相变，到543K就基本实现了这一结构相变，使得这一相变温度比其他文献中报道的又降低 了许多. 关键词： 2')" href="#">纳米TiO₂ 溶胶_凝胶法 结构相变 晶粒生长动力学     

Accelerated life ac conductivity measurements of CRT oxide cathodes

The ac conductivity measurements have been carried out for the activated Ba/SrO cathode with additional 5% Ni powder for every 100 h acceleration life time at the temperature around 1125 K. The ac conductivity was studied as a function of temperature in the range 300-1200 K after conversion and activation of the cathode at 1200 K for 1 h in two cathodes face to face closed configuration. The experimental results prove that the hopping conductivity dominate in the temperature range 625-770 K through the traps of the WO₃ associate with activation energy E_a = 0.87 eV, whereas from 500-625 K it is most likely to be through the traps of the Al₂O₃ with activation energy of E_a = 1.05 eV. The hopping conductivity at the low temperature range 300-500 K is based on Ni powder link with some Ba contaminants in the oxide layer stricture which indicates very low activation energy E_a = 0.06 eV.     

Electric-field-dependent charge delocalization from dopant atoms in silicon junctionless nanowire transistor

We study electric-field-dependent charge delocalization from dopant atoms in a silicon junctionless nanowire transistor by low-temperature electron transport measurement. The Arrhenius plot of the temperature-dependent conductance demonstrates the transport behaviors of variable-range hopping(below 30 K) and nearest-neighbor hopping(above 30 K).The activation energy for the charge delocalization gradually decreases due to the confinement potential of the conduction channel decreasing from the threshold voltage to the flatband voltage. With the increase of the source–drain bias, the activation energy increases in a temperature range from 30 K to 100 K at a fixed gate voltage, but decreases above the temperature of 100 K.     

Dimer and cluster formation in C60 photoreaction

The process of phototransformation in C₆₀ was analysed by means of Raman spectroscopy for single crystals irradiated at various temperatures between 80 K and 450 K. The activation window for the transformation process was found to be between the temperature of the first order phase transition of 260 K and an upper temperature of about 400 K. Detailed features of the resulting spectra were found to depend on the transformation temperature. From a comparison with ab initio calculations of Porezag et al. the material irradiated at high temperatures could be assigned to a C₆₀ dimer whereas the material phototransformed at room temperature could not be identified with a simple cluster.     

Effects of photoexcitation on the current transport mechanism in amorphous indium selenide thin films

The effect of photoexcitation on the current transport mechanism in amorphous indium selenide thin films was studied by means of dark and illuminated conductivity measurements as a function of temperature. Analysis of the dark electrical conductivity in the temperature range 110–320 K reveals behaviour characteristic of carriers excited to the conduction band and thermally assisted variable-range hopping (VRH) at the Fermi level above 280 K and below 220 K, respectively. In the temperature range 220–280 K, a mixed conduction mechanism was observed. A conductivity activation energy of ～300 meV (above 280 K), a density of localised states (evaluated assuming a localisation length of 5 Å) of 1.08 × 10²¹ cm^?3 eV^?1, an average hopping distance of 20.03 Å (at 120 K) and an average hopping energy of 27.64 meV have been determined from the dark electrical measurements. When the sample was exposed to illumination at a specific excitation flux and energy, the values of the conductivity activation energy, the average hopping energy and the average hopping range were significantly decreased. On the other hand, the density of localised states near the Fermi level increased when the light flux was increased. Such behaviour was attributed to a reversible Fermi level shift on photoexcitation.     

Transport effects in single-crystal La0.82Ca0.18MnO3

This paper reports experimental data on the temperature dependences of the electrical resistivity, magnetoresistance, thermopower, magnetothermopower, and normal and spontaneous Hall coefficients of the La_0.82Ca_0.18MnO₃ single crystal with a Curie temperature of 180 K. It is shown that, at low temperatures, electrons are the majority carriers. For T < 110 K, the electrical resistivity depends substantially on the position of the magnetization vector with respect to the crystallographic axes, which implies a significant role played by the spin-orbit interaction. For T > 137 K, holes are dominant. In the vicinity of the Curie temperature, electrical conduction is effected primarily by holes activated to the mobility edge. The local activation energy of the resistivity exhibits a critical behavior. The temperature dependence of the local activation energy is determined by spin correlation functions. For T > 240 K, the activation energy does not depend on temperature.     

The Melting Temperature of 99.97 wt.% Al Estimated from Activation Energy for Viscous Flow

The viscous flow phenomenon in molten aluminium and the viscosity, in the vicinity of its melting temperature, was analyzed. When the temperature decreases, both the viscosity and the activation energy for viscous flow increase. This is explained on the basis of the atomic rearrangement due to interatomic interactions prior to the separation of the solid phase. The latter was found to be nonlinear as the temperature is decreased wherein the solid phase is separated from the liquid. The second derivative of the activation energy for viscous flow with respect to temperature was found to show discontinuity in the vicinity of the melting temperature. Thus, the second derivative offers a way of estimating the melting temperature of metals. Our estimations indicate that the break of the second derivative vs. temperature could be observed at 938 K.     

Influence of sintering conditions and laser irradiation on electroconductivity of CuO/Ag ceramics

We study the influence of different thermal treatments and pulsed laser irradiation on the temperature dependence of resistance and activation energy of ceramic samples of copper oxide. For studies of influence of impurity, thin film of silver was deposited on some samples prior to laser action. It is revealed that the temperature dependence of resistance of all samples has in the range 80–300 K a semiconductor nature and the activation energy of resistance varies within the limits 0.19–0.48 eV. It is established that the activation energy decreases with rise of the sintering temperature and quenching cooling increases the activation energy. Laser treatment reduces the dependence of activation energy on sintering temperature and deposition of silver upon the sample before laser treatment eliminates this dependence completely.     

Thermal analysis, Raman spectroscopy and complex impedance analysis of Cu2+-doped KDP

Raman spectroscopy and differential thermal analysis (DTA) and thermogravimetric analysis have been carried out on Cu-doped KH₂PO₄ (Cu-KDP). X-ray diffraction powder data reveal that the structure of the KDP crystal does not change with the additive Cu²⁺ ion. DTA analysis and Raman study of Cu-KDP as a function of temperature reveal that this compound undergoes two phase transitions at about Ttr =453 and 473 K. The electrical conductivity measurements on polycrystalline pellet of Cu-KDP (5) are performed from room temperature (RT) up to 495 K. Only one phase transition is observed at 470 K. The activation energy in the migration is 0.42 eV in the temperature range from RT to 470 K. For temperature above 470 K, the activation energy of the superprotonic phase is 1.87 eV.     

Investigation of the dynamical behaviour of the FH(CN−) centre in KCl with temperature dependent endor spectroscopy

Abstract

The temperature dependence of the electron nuclear double resonance (ENDOR) spectra of F_H(CN^?) centres in KCl was investigated in the temperature range between 10–220 K. At the lowest temperature of 10 K only one CN^? orientation with respect to the F centre electron is present, in which the nitrogen is thought to be nearer to the F-electron than the carbon. With the very small thermal activation energy of 2.9 meV the opposite orientation is occupied. The superhyperfine interactions of those first shell K nuclei nearest to CN^? and of the ¹³C interaction of the CN^? molecule are strongly temperature dependent between 10 and 60 K, following an exponential law with a thermal activation energy of 4.2 meV. It is assumed that a soft local mode involving those two nearest K nuclei and the CN^? is causing the strong temperature dependence. The shf interactions of ¹⁴N nuclei have not been seen, probably because of the dynamical effects.     

Effect on thermoluminescence parameters of biotite mineral due to thermal quenching

The Thermally Stimulated Luminescence (TSL) at room temperature X-ray irradiated natural biotite in form of micro-grain powder was studied under various heating rates. TSL peaks showed at temperatures 393 K, 399.6 K, 403.5 K, 404.5 K, 406.9 K at their respective heating rates 2 K/s, 4 K/s, 6 K/s, 8 K/s and 10 K/s. The effect of thermal quenching on thermoluminescence parameters such as peak maximum temperature, peak area, FWHM, geometrical symmetry factor, the activation energy were investigated. From the symmetry factor it is clear that the TL glow curve follows the first order kinetics for the lowest heating rate, but as the heating rate increases it defers from the first order. The activation energies for each heating rates were calculated by using Chen peak shape methods for general order kinetics and found to be decreased for higher heating rates. When activation energy is calculated by variable heating rate method it is observed that the method overestimated the value of activation energy and pre-exponential frequency factor significantly due to thermal quenching.