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In-Situ High Pressure Raman Spectrum and Electrical Property of PbMoO4
YU Cui-Ling, YU Qing-Jiang, GAO Chun-Xiao, LIU Bao, HAO Ai-Min, HE Chun-Yuan, HUANG Xiao-Wei, ZHANG Dong-Mei, CUI Xiao-Yan, LI Ming, LI Dong-Mei, Ma Yan-Zhang, ZOU Guang-Tian
Chin. Phys. Lett. 2007, 24 (8):
2204-2207
.
In-situ high pressure Raman spectra and electrical conductivity measurements of scheelite-structure compound PbMoO4 are presented. The Raman spectrum of PbMoO4 is determined up to 26.5GPa on a powdered sample in a diamond anvil cell (DAC) under nonhydrostatic conditions. The PbMoO4 gradually experiences the transformation from the crystal to amorphous between 9.2 and 12.5GPa. The crystal to amorphous transition may be due to the mechanical deformation and the crystallographic transformation. Furthermore, the electrical conductivity of PbMoO4 is in situ measured accurately using a microcircuit fabricated on a DAC based on the van der Pauw method. The results show that the electrical conductivity of PbMoO4 increases with increases of pressure and temperature. At 26.5GPa, the electrical conductivity value of PbMoO4 at 295K is 1.93×10-4S/cm, while it raises by one order of magnitude at 430K and reached 3.33×10-3S/cm. However, at 430K, compared with the electrical conductivity value of PbMoO4 at 26.5GPa, it
drops by about two order magnitude at 7.4GPa and achieves 2.81×10-5S/cm. This indicates that the effect of pressure on the electrical conductivity of PbMoO4 is more obvious than that of temperature.
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Measurement of Gamma-Rays from 11ΛB and 12ΛC
FU Yuan-Yong, ZHOU Shu-Hua, T. Koike, S. Kinoshita, Y. Ma, Y. Miura, K. Miwa, Y. Miyagi, K. Shirotori, T. Suzuki, H. Tamura, K. Tsukada, M. Ukai, K. Futatsukawa, K. Hosomi, M. Kawai, M. Mimori, N. Terada, N. Maruyama, K. Aoki, H. Fujioka, Y. Kakiguchi, T. Nagae, D. Nakajima, H. Noumi, T. Takahashi, T.N. Takahashi, A. Toyota, M. Dairaku, T. Fukuda, S. Minami, W. Imoto, S. Ajimura, K. Tanida
Chin. Phys. Lett. 2007, 24 (8):
2216-2218
.
From the 12C(π+, K+)12ΛC reaction, the γ-rays of 261.6±0.24keV (7/2+→to
5/2+) and 1481.7±0.7keV (1/2+±5/2+) of 11ΛB, and 2667.3±2.8keV (12-→to 21-) of 12ΛC hypernuclei have been identified using a large germanium detector array Hyperball2 at K6 beam line of KEK. The observed energies of the transitions 1481.7keV and 261.6keV are significantly different from the values predicted by the shell model using the △ and SN parameters determined from the 7ΛLi data.
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Properties of All-Solid Square-Lattice Photonic Bandgap Fibres
SHI Qing, KAI Gui-Yun, WANG Zhi, YUE Yang, DU Jiang-Bing, FANG Qiang, LIUYan-Ge, LV Fu-Yun, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2007, 24 (8):
2259-2262
.
Properties of all-solid square-lattice photonic bandgap fibres are studied for the first time to the best of our knowledge. Using the plane-wave expansion method and finite element method, we investigate the mode, effective area, confinement loss and dispersion of such fibres. The simulation results demonstrate that the proposed effective mode area of all-solid square-lattice photonic bandgap fibres is 1.25 times larger than triangular-lattice ones and the confinement loss of the fibres is no more than 0.1dB/m within the bandgap.
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Compression Behaviour of Bulk Metallic Glasses and Binary Amorphous Alloy
LI Gong, LIU Jing, LIU Ri-Ping
Chin. Phys. Lett. 2007, 24 (8):
2323-2326
.
The compression properties of Zr41Ti14Cu12.5Ni10Be22.5, Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glasses and Ni77P23 binary amorphous alloy are investigated at room temperature up to 24GPa, 39GPa and 30.5GPa, respectively, using in-situ high pressure energy dispersive x-ray
diffraction with a synchrotron radiation source. The pressure--volume
relationship of Ni77P23 amorphous alloy is consistent well with the second order Birch--Murnaghan (B-M) equation within the experimental pressure range. However, under higher pressure, the experimental data of Zr-based specimens deviate from the B-M equation. Compare to the binary amorphous alloy, less excess free volume existing in the bulk metallic glass and multi-component atomic configuration results in a two-stage relationship between
compressibility and pressure.
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Evolution of Voronoi/Delaunay Characterized Micro Structure with Transition from Loose to Dense Sphere Packing
AN Xi-Zhong
Chin. Phys. Lett. 2007, 24 (8):
2327-2330
.
Micro structures of equal sphere packing (ranging from loose to dense
packing) generated numerically by discrete element method under different vibration conditions are characterized using Voronoi/Delaunay tessellation, which is applied on a wide range of packing densities. The analysis on micro properties such as the total perimeter, surface area, and the face number distribution of each Voronoi polyhedron, and the pore size distribution in each Voronoi/Delaunay subunit is systematically carried out. The results show that with the increasing density of sphere packing, the Voronoi/Delaunay pore size distribution is narrowed. That indicates large pores to be gradually substituted by small uniformed ones during densification. Meanwhile, the distributions of face number, total perimeter, and surface area of Voronoi polyhedra at high packing densities tend to be narrower and higher, which is in good agreement with those in random loose packing.
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Plastic Deformation of Fine-Grained Al--Cu--Fe--(B) Icosahedral Poly-Quasicrystals at Elevated Temperature
WANG Jian-Bo, MA Jia-Yan, LU Lu, XIONG Dong-Xia, ZHAO Dong-Shan, WANG Ren-Hui
Chin. Phys. Lett. 2007, 24 (8):
2331-2334
.
Fine-grained Al--Cu--Fe--(B) icosahedral poly-quasicrystals (IQCs) as the main materials and fine-grained Al--Pd--Mn IQCs as the supplements, both prepared by powder metallurgy, are uniaxially deformed at various temperatures and strain rates. The systematic study shows the dependences of curves of the true stress versus true strain on several parameters, such as temperature, strain rate and grain size. For Al--Cu--Fe IQCs with grain sizes of about 10--30μm, QC-specific intra-granular softening drop appears in the deformation curves at lower temperatures and/or faster strain rates, but disappears in those curves at higher temperatures and/or slower strain rates, which suggests that the inter-granular effects such as grain-boundary sliding
should be taken into account to interpret the continuous hardening, similarly to conventional poly-crystals. For Al--Cu--Fe-B IQCs with smaller grain sizes of about 1μm and fine-grained Al--Pd--Mn IQCs with grain sizes of about 10μm, QC-specific intra-granular softening drop is absent for all the deformation curves at the possible lowest temperature and fastest strain rate. This implies that the smaller the grain size, the more the inter-granular contribution. At the same time, due to the rapid recovery caused by intense diffusion in small-sized grains, the intra-granular quasicrystal lattice reorders rapidly from
disordering, which also inhibits the intra-granular softening drop to some extent.
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Measurement and Analysis of Spall Characteristics of High-Pure Aluminium at One-Dimensional Strain Loading
QI Mei-Lan, HE Hong-Liang, YAN Shi-Lin
Chin. Phys. Lett. 2007, 24 (8):
2338-2340
.
With an impact velocity varying from 196.9m/s to 317.9m/s and ratios of flyer/sample thickness of 2:4 and 3:6, the free-surface velocity profiles of the shock compressed high purity aluminium (HPA 99.999%) samples are measured with a velocity interferometer system for any reflector. Based on the vibrating features of the velocity profiles, the damage behaviour of HPA is analysed. The results indicate that the vibrating amplitude increases with increasing shock stress, and the subsequent reverberations describing the spall become more obvious. When the shock stress in the material is below a critical or smaller than the threshold level, the free-surface velocity profile replicates virtually the form of the compression pulse inside the sample. When the impact stress exceeds a critical value (1.4GPa), the micro damage would
appear, and the free-surface velocity profile changes significantly, showing a series of short-duration reverberations in the profile. When the impact stress exceeds the threshold of damage, a compressive disturbance called the ``spall pulse'' appears in the free-surface velocity profile, and the subsequent reverberation becomes regular again. The measured spall strength of HPA is much higher than those of commercially pure aluminium reported in many references. In addition, the strength of HPA is similar to that of single-crystal aluminium.
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Dislocation Reduction Mechanisms in Gallium Nitride Films Grown by Canti-Bridge Epitaxy Method
XING Zhi-Gang, WANG Jing, PEI Xiao-Jiang, WAN Wei, CHEN Hong, ZHOU Jun-Ming
Chin. Phys. Lett. 2007, 24 (8):
2353-2356
.
By using the special maskless V-grooved c-plane sapphire as the substrate, we previously developed a novel GaN LEO method, or the so-called canti-bridge epitaxy (CBE), and consequently wing-tilt-free GaN films were obtained with low dislocation densities, with which all the conventional difficulties can be overcome [J. Vacuum Sci. Technol. B 23 (2005) 2476]. Here the evolution manner of dislocations in the CBE GaN films is investigated using transmission electron microscopy. The mechanisms of dislocation reduction are discussed.
Dislocation behaviour is found to be similar to that in the conventional LEO GaN films except the enhanced dislocation-combination at the coalescence boundary that is a major dislocation-reduction mechanism for the bent horizontal-propagating dislocations in the CBE GaN films. The enhancement of this dislocation-combination probability is believed to result from the inclined shape and the undulate morphology of the sidewalls, which can be readily obtained in a wide range of applicable film-growth conditions during the GaN CBE process. Further development of the GaN CBE method and better crystal-quality of the GaN film both are expected.
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An Electroluminescence Delay Time Model of Bilayer Organic Light-Emitting Diodes
LI Hong-Jian, ZHU Ru-Hui, LI Xue-Yong, YANG Bing-Chu
Chin. Phys. Lett. 2007, 24 (8):
2394-2397
.
Based on the mechanism of injection, transport and recombination of the charge carriers, we develop a model to calculate the delay time of electroluminescence (EL) from bilayer organic light emitting diodes. The effect of injection, transport and recombination processes on the EL delay time is discussed, and the relationship between the internal interface barrier and the recombination time is revealed. The results show that the EL delay time is dominated by the recombination process at lower applied voltage and by the transport process at higher applied voltage. When the internal interface barrier varies from 0.15eV to 0.3eV, the recombination delay time increases rapidly, while the internal interface barrier exceeds about 0.3eV, the dependence of the recombination delay time on applied voltage is almost
undiversified, which may serve as a guideline for designing of a high-speed EL response device.
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Controlled Growth of Zn-Polar ZnO Films on Al-Terminated α-Al2O3(0001) Surface by Using Wurtzite MgO Buffer
YUAN Hong-Tao, LIU Yu-Zi, WANG Xi-Na, LI Han-Dong, WANG Yong, ZENG Zhao-Quan, MEI Zeng-Xia, DU Xiao-Long, JIA Jin-Feng, XUE Qi-Kun, ZHANG Ze
Chin. Phys. Lett. 2007, 24 (8):
2408-2411
.
The controlled growth of Zn-polar ZnO films on Al-terminated αAl2O3 (0001) substrates is investigated by the radio-frequency plasma-assisted molecular beam epitaxy method. Prior to the growth, αAl2O3 (0001) surface is modified by an ultrathin MgO layer, which serves as a uniform template for epitaxy of
Zn-polar ZnO films. The microstructures of ZnO/MgO/Al2O3 interface are investigated by in-situ reflection high-energy electron diffraction observations and ex-situ high-resolution transmission electron microscopy characterization. It is found that under Mg-rich condition, the achievement of the wurtzite MgO ultrathin layer plays a key role in the subsequent growth of Zn-polar ZnO. An
interfacial atomic model is proposed to explain the mechanism of polarity selection of both MgO and ZnO films.
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Measuring Grüneisen Parameter of Lead by High Pressure-Jump Method
HUANG Dai-Hui, LIU Xiu-Ru, SU Lei, HU Yun, LV Shi-Jie, LIU Hai-Long, HONG Shi-Ming
Chin. Phys. Lett. 2007, 24 (8):
2441-2443
.
Using the technology of pressure jump, variations of temperature associated with pressure from 2.4GPa to 4.6GPa are measured for lead. The Grüneisen parameter is calculated from the thermodynamic relation γ= (Ks/T) (∂T/ ∂P)s, in which substitution of △T/△P for ∂T/∂P at median pressure is strictly justified. The correction of temperature change is carried out by analysing the
experimental data, which makes the process more approaching to an
adiabatic condition. The calculated values of △T/△P and γ gradually decrease with the increasing pressure. The decrease trend is consistent with the previous work. The γ values in the range of 2--3GPa are averagely higher than the results of Ramakrishnan et al., indicating the effect of temperature correction. The improved method is promising for measurements of Grüneisen parameter to higher pressure range.
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Cosmological Constant or Variable Dark Energy?
XU Li-Xin, ZHANG Cheng-Wu, LIU Hong-Ya
Chin. Phys. Lett. 2007, 24 (8):
2459-2462
.
Selection statics of the Akaike information criterion (AIC) model and the Bayesian information criterion (BIC) model are applied to the Λ-cold dark matter (ΛCDM) cosmological model, the constant equation of state of dark energy, w=constant, and the parametrized equation of state of dark energy, w(z)=w_0+w_1 z/(1+z), to determine which one is the better cosmological model to describe the evolution of the universe by combining the recent
cosmic observational data including Sne Ia, the size of baryonic acoustic oscillation (BAO) peak from SDSS, the three-year WMAP CMB shift parameter. The results show that AIC, BIC and current datasets are not powerful enough to discriminate one model from the others, though odds suggest differences between them.
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83 articles
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