Search

In recent years, metal halide perovskites have received extensive attention due to their superior optoelectronic properties and solution processability, which also become a research hotspot in the field of optoelectronics. Among all the perovskite optoelectronics applications, perovskite light-emitting diode (LED) becomes one of the important research topics because it is likely to be used in the next-generation display technique. Based on the high photoluminescence quantum yield (PLQY), facilely tunable bandgaps, and sharp emission of perovskite material, the external quantum efficiency of perovskite LED has increased from less than 1% to over 20% within only five years, showing the most rapid development speed in the LED field. During the 5-year exploration of perovskite LEDs, researchers have focused their efforts on how to realize the crystal-growth control in the perovskite film formation process, enhance PLQY of the perovskite films, and improve the performance of perovskite LEDs. Among all the approaches, the utilization of organic additives including small molecules and polymers proves to be an effective strategy. Here, in this article, we review the recent advances in metal halide perovskite LEDs based on the strategy of organic-additive treatment. We also analyze and discuss the interaction between organic additive and perovskite crystal as well as its influence on the performance of perovskite LED. In the end, we discuss the challenges remaining in perovskite LEDs and the prospects for perovskite LEDs.

Although the nonlinear interactions between a single short gravity wave and a long wave can be solved analytically, the solution is less tractable in more general cases involving multiple short waves. In this work we present a numerical method of studying nonlinear interactions between a long wave and multiple short harmonic waves in infinitely deep water. Specifically, this method is applied to the calculation of the temporal and spatial evolutions of the surface elevations in which a given long wave interacts with several short harmonic waves. Another important application of our method is to quantitatively analyse the nonlinear interactions between an arbitrary short wave train and another short wave train. From simulation results, we obtain that the mechanism for the nonlinear interactions between one short wave train and another short wave train (expressed as wave train 2) leads to the energy focusing of the other short wave train (expressed as wave train 3). This mechanism occurs on wave components with a narrow frequency bandwidth, whose frequencies are near that of wave train 3.

This paper studies the effects of He atom on the spin-polarized electronic properties of nickel under pressures using ab initio pseudopotential plan-wave method. Under high pressures, the compound of NiHe0.25 can exist and heliumbubble can not create in Ni. A pressure-induced ferromagnetic to paramagnetic phase transition has been predicted in NiHe0.25 at about 218 GPa. It is found that under pressures, the magnetic property of Ni atoms is more strongly affected by He atom than by H atom and that the behaviour of He atom in Ni are completely different from that of H atom, like the bonding characteristics and the electron transfer.

Instead of the conventional graphite, new additional reducing agents (diamond, silicon, metal elements, etc.) have been mixed with zinc oxide (ZnO) powder to fabricate ZnO micro/nanostructures by a thermal vapour transport method. Due to the strong reducibility for those additions, the corresponding heating temperature is decreased by 100-500° C compared to the case of graphite, which subsequently decreases the corresponding growth temperature for the products. Being placed separately for the powder sources of ZnO and addition, a vapour-vapour reduction-oxidation reaction mechanism between the sources is proposed as an important channel to fabricate ZnO. Photoluminescence and magnetic examinations indicate that the ZnO products synthesized have strong ultraviolet (visible) emissions and are room-temperature ferromagnetic, meaning that the products are available for applications.

Crystal structures and optical properties of the δ−O2 phase and the −O8 phase have been investigated by using the ab initio pseudopotential plane-wave method. It is found that the phase transition is of the first order with a discontinuous volumetric change from the antiferromagnetic δ−O2 phase to the nonmagnetic −O8 phase, consistent with the experimental findings. The energy band calculations show that the direct band gap changes into an indirect band gap after the phase transition. The apparent change in the optical properties can be used for identifying the phase transition from δ−O2 to −O8.

The equilibrium lattice constant, the cohesive energy and the electronic properties of light metal hydrides Li XH3and XLiH3 (X = Be, B or C) with perovskite lattice structures have been investigated by using the pseudopotential plane-wave method. Large energy gap of LiBeH3 indicates that it is insulating, but other investigated hydrides are metallic. The pressure-induced metallization of LiBeH3 is found at about 120 GPa, which is attributed to the increase of Be-p electrons with pressure. The electronegativity of the p electrons of X atom is responsible for the metallicity of the investigated Li XH3 hydrides, but the electronegativity of the s electrons of X atom plays an important role in the metallicity of the investigated XLiH3 hydrides. In order to deeply understand the investigated hydrides, their optical properties have also been investigated. The optical absorption of either LiBeH3 or BeLiH3 has a strong peak at about 5eV, showing that their optical responses are qualitatively similar. It is also found that the optical responses of other investigated hydrides are stronger than those of LiBeH3 and BeLiH3 in lower energy ranges, especially in the case of CLiH3.

An investigation on the structural stabilities and electronic properties of SrX (X = S, Se and Te) under high pressure is conducted using the first-principles calculation based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. Our results demonstrate that the sequence of the pressure-induced phase transition of the three compounds is the NaCl-type (B1) structure (Fm3m) to the CsCl-type (B2) structure (Pm3m). The phase transition and the metallization pressures are determined theoretically. The pressure effect on the optical properties is discussed. The results are compared with the previous calculations and experimental data.

High rate (> 50 μm/h) growth of homoepitaxial single-crystal diamond (SCD) is carried out by microwave plasma chemical vapour deposition (MPCVD) with added nitrogen in the reactant gases of methane and hydrogen, using a polycrystalline-CVD-diamond-film-made seed holder. Photoluminescence results indicate that the nitrogen concentration is spatially inhomogeneous in a large scale, either on the top surface or in the bulk of those as-grown SCDs. The presence of N-distribution is attributed to the facts: (i) a difference in N-incorporation efficiency and (ii) N-diffusion, resulting from the local growth temperatures changed during the high-rate deposition process. In addition, the formed nitrogen-vacancy centres play a crucial role in N-diffusion through the growing crystal. Based on the N-distribution observed in the as-grown crystals, we propose a simple method to distinguish natural diamonds and man-made CVD SCDs. Finally, the disappearance of void defect on the top surface of SCDs is discussed to be related to a filling-in mechanism.

High-pressure phases of BC3 are studied within the local density approximation under the density functional theory framework. When the pressure reaches 20 GPa, the layered BC3 that is a semiconductor at ambient pressure, becomes metallic. As the pressure increases, the material changes into a network structure at about 35 GPa. To understand the mechanism of phase transitions, band structure and density of states are discussed. With the increase of pressure, the width of bands broadens and the dispersion of bands enlarges. Additionally, the density of states of the network bears great resemblance to that of diamond. Formation of the sp3 bonding in the network is the main reason for the structural transformation at 35 GPa.

The effects of pressure on the fluorescence emission and Raman spectra of 1,4-bis[(4-methyloxyphenyl)-1,3,4-oxadiazolyl]- 2,5-bisheptyloxyphenylene (OXD-2) and on the fluorescence emission spectra of 1,4-bis[(4-methylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-1) are investigated using a diamond anvil cell. With the increase of pressure, the intensity of the fluorescence emission increases and reaches maxima at 13GPa for OXD-1 and at 9.6GPa for OXD-2. The effect of pressure on the peak position of the emission shows a similar trend, red shift with the increase of pressure. But at higher pressures, the intensity of emission drops down dramatically. The Raman spectra of OXD-2 indicate that there appears a structural change at ca 3GPa.

The electrical resistivity variation of 1,4-bis[(4-methylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-1) microcrystal is studied under variable pressure and temperature conditions by a quasi four-probe method in a diamond anvil cell. The sample resistivity is calculated with a finite element analysis method. The temperature and pressure dependencies of resistivity of OXD-1 microcrystal are measured up to 150 degrees C and 15 GPa. The resistivity decrease with temperature increasing indicates that OXD-1 exhibits an organic-semiconductor transport property in the experimental pressure region. With pressure increasing, the resistivity of OXD-1 increases firstly and reaches the maximum at about 6.2 GPa, and then begins to decrease as the pressure increases continuously. In situ x-ray diffraction data under pressure provide obvious prove that the anomaly of resistivity variation at 6.2 GPa is caused by the pressure-induced amorphism of OXD-1.

An effective method is developed to fabricate metallic microcircuits in diamond anvil cell (DAC) for resistivity measurement under high pressure. The resistivity of nanocrystal ZnS is measured under high pressure up to 36.4 GPa by using designed DAC. The reversibility and hysteresis of the phase transition are observed. The experimental data is confirmed by an electric current field analysis accurately. The method used here can also be used under both ultrahigh pressure and high temperature conditions.

Structural behaviour of cyclo-octane under high pressure is studied by using a synchrotron x-ray source in a diamond anvil cell (DAC) up to 40.2 GPa at room temperature. The cyclo-octane firstly solidifies to the triclinic phase at 0.87GPa. With the increasing pressure, the phase of cyclo-octane changes to the tetragonal phase at about 6.0 GPa and then transforms to amorphous phase above 18.2 GPa, which is kept till to 40.2 GPa. All the phase transitions of cyclo-octane are irreversible.

We perform an ab initio study on the electronic structure and charge density of the e-oxygen under high pressure, which is obtained by powder x-ray diffraction experiment recently. Our results show that the hybridization among the σg*, πu and πg* bands in the e-oxygen are not significant even at megabar pressure. Pressure-induced metallization occurs due to the band overlapping near the Fermi level at about 50 GPa. A new network along the b-axis is formed and the O8 characteristic in the e phase disappears above 50 GPa even though the symmetry remains unchanged.

The lattice dynamics of rhombohedral CaC6 is studied as a function of pressure to probe its high pressure phase with low superconducting transition temperature using the density functional liner-response theory. The pressure-induced phase transition in CaC6 is attributable to the softening transverse acoustic (TA) phonon mode at the zone boundary X (0.5, 0.0, 0.5) point. The high pressure phase is then explored by performing fully structural optimization in the supercell which accommodates the atomic displacements corresponding to the eigenvectors of the unstable mode of TA(X). The high-pressure phase is predicted to be a monoclinic unit cell with space group P21/m.

The compressional behaviour of natural pyrope garnet is investigated by using angle-dispersive synchrotron radiation x-ray diffraction and Raman spectroscopy in a diamond anvil cell at room temperature. The pressure-induced phase transition does not occur under given pressure. The equation of state of pyrope garnet is determined under pressure up to 25.3 GPa. The bulk modulus KT0 is 199 GPa, with its first pressure derivative K'T0 fixed to 4. The Raman spectra of pyrope garnet are studied. A new Raman peak nearly at 743 cm−1 is observed in a bending vibration of the SiO4 tetrahedra frequency range at pressure of about 28 GPa. We suggest that the new Raman peak results from the lattice distortion of the SiO4 tetrahedra. All the Raman frequencies continuously increase with the increasing pressure. The average pressure derivative of the high frequency modes (650–1000 cm−1) is larger than that of the low frequency (smaller than 650 cm−1). Based on these data, the mode Gruneisen parameters for pyrope are obtained.

The structural transition of bulk and nano-size Gd2O3:Eu are studied by high pressure energy disperse x-ray diffraction (XRD) and high pressure photoluminescence. Our results show that in spite of different size of Gd2O3 particles, the cubic structure turns into a possible hexagonal one above 13.4 GPa. When the pressure is released, the sample reverses to the monoclinic structure. No cubic structure presents in the released samples. That is to say, the compression and relaxation of the sample leads to the cubic Gd2O3:Eu then turns into the monoclinic one.

Electrical properties of stoichiometric iron sulfide (FeS) are investigated under high pressure with a designed diamond anvil cell. The process of phase transition is reflected by changing the electrical conductivity under high pressure, and the conductivity of FeS with the NiAs structure is found to be much smaller than other phases. Two new phase transitions without structural change are observed at 34.7GPa and 61.3 GPa. The temperature dependence of the conductivity is found to be similar to that of a semiconductor when the pressure is higher than 35 GPa.

We perform the in-situ conductivity measurement on BaF2 at high pressure using a microcircuit fabricated on a diamond anvil cell. The results show that BaF2 initially exhibits the electrical property of an insulator at pressure below 25 GPa, it transforms to a wide energy gap semiconductor at pressure from 25 to 30 GPa, and the conductivity increases gradually with increasing pressure from 30 GPa. However, the metallization predicted by theoretical calculation at 30–33 GPa cannot be observed. In addition, we measure the temperature dependence of the conductivity at several pressures and obtain the relationship between the energy gap and pressure. Based on the experimental data, it is predicted that BaF2 would transform to a metal at about 87 GPa and ambient temperature. The conductivity of BaF2 reaches the order of 10−3Ω−1cm−1 at 37 GPa and 2400 K, the superionic conduction is not observed during the experiments, indicating the application of pressure elevates greatly the transition temperature of the superionic conduction.

Nanocrystalline molybdenum nitride (γ-Mo2N) with the cubic structure is prepared by the direct-current arc discharge method in N2 gas, using metal Mo or W rod as a cathode. The x-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to characterize the product. It is found that the conversion of Mo to γ-Mo2N and affinity of Mo to N2 are determined by the nitrogen pressure. Moreover, we compare the effect of Mo and W rod as a cathode for preparing γ-Mo2N. The average size of γ-Mo2N particles is about 5 nm. The rapid quenching mechanism can be used to explain the formation of nanocrystalline γ-Mo2N.

The composition-dependent thermoelectric properties of lead telluride (PbTe) doped with bismuth telluride (Bi2Te3), antimony telluride (Sb2Te3) and (BiSb)2Te3 have been studied at room temperature. All the samples exhibit small thermal conductivity. The figures of merit, 7.63, 1.03 and 8.97×10−4, have been obtained in PbTe with these dopants, respectively. These values are several times higher than those of PbTe containing other dopants with small grain sizes. The high thermoelectric performance is explained by electronic topological transition induced by alloying. The results indicate that these dopants are effective to enhance the thermoelectric performance of PbTe.

In situ resistance measurement of Graphitic-C3N4 has been performed under high pressure in a diamond anvil cell. The result reveals that there are changes of electron transport behaviour. As the pressure increases from ambient to 30 GPa, three abnormal resistance changes can be found at room temperature and two are found at 77 K. The abnormal resistance dropped at 5 GPa is close to the phase transition pressure from the Pm2 structure to the p structure predicted by Lowther et al. [Phys. Rev. B 59 (1999) 11683] Another abnormal change of resistance at 12 GPa is related to the phase transition from g-C3N4 to cubic-C3N4 [Teter and Hemley, Science 271 (1996) 53].

In-situ energy dispersive x-ray diffraction on ZnS nanocrystalline was carried out under high pressure by using a diamond anvil cell. Phase transition of wurtzite of 10 nm ZnS to rocksalt occurred at 16.0 GPa, which was higher than that of the bulk materials. The structures of ZnS nanocrystalline at different pressures were built by using materials studio and the bulk modulus, and the pressure derivative of ZnS nanocrystalline were derived by fitting the equation of Birch-Murnaghan. The resulting modulus was higher than that of the corresponding bulk material, which indicates that the nanomaterial has higher hardness than its bulk materials.

The Raman spectra of PbZr0.3Ti0.7O3 for different grain size as well as at high temperature and high pressure have revealed that its structure is transformed from tetragonal to quasi-cubic phase with decreasing grain size. The phase transition temperature drops down to a lower temperature and the pressure-induced phase transition can be correlated with the diffuse phase transition.

High quality diamond films have been deposited on Si(100) mirror surface without using any surface pretreatment such as abrasive diamond scratching, diamond-like carbon predeposition or oil treatment. The experiments are carried out in the hot filament chemical vapour deposition system by using the mixture of methane, hydrogen and oxygen. The films show the well-defined facets and are confirmed by Raman spectroscopy and scanning electron microscopy to be high quality diamond films. In this deposition process, higher substrate temperature, high filament temperature and oxygen addition play the important roles in diamond nucleation on the mirror-smooth Si(100) surface.

We study the energy-dispersive x-ray diffraction and Raman scattering of LiTaO3 at high pressure. The result remains stable up to 36 GPa. The average isothermal bulk modulus and its pressure derivative are obtained to be k0 = (225±6) GPa and k0' = 1.3±0.5 at zero pressure by the Birch-Murnaghan equation of state and the ``universal'' equation of state. The linear incompressibility of LiTaO3 between the a- and c-directions differs by a factor of four, which shows that the compression is anisotropic.

P-type semiconducting polycrystalline diamond thin films doped with boron were synthesized on single crystalline silicon substrate by thermal chemical vapor deposition from a tungsten filament and placing boron-contained substance (boron nitride or elemental boron) on sample holder. The films were determined to be the high quality diamond by Raman spectroscopy, x-ray diffraction and scanning electron microscope measurements. The doping properties of boron were measured by Hall method and infrared absorption.

Diamond films have been deposited on porous silicon with microwave plasma chemical vapour deposition method. Nucleation density and site have been observed and analyzed by using scanning electron micrography. Experimental results showed that the nucleation density changes with the porosity and the nucleation occurs mostly on the edge of the pores. Reasons of these phenomena are discussed.

Diamond films have been grown on high pressure synthesized cubic boron nitride (c-BN) particles by hot-filament chemical vapor deposition method, and heteroepitaxial diamond films on the c-BN (100) facets with no-evident defects were obtained, but polycrystalline diamond films were formed only on the c-BN (111) facets.

The effect of external quasi-hydrostatic pressure on the inverse spinel structure of LiCuVO4 was studied in this paper. High-pressure synchrotron X-ray diffraction and Raman spectroscopy measurements were carried out at room temperature up to 35.7 and 40.3 GPa, respectively. At a pressure of about 20 GPa, both Raman spectra and X-ray diffraction results indicate that LiCuVO4 was transformed into a monoclinic phase, which remained stable up to at least 35.7 GPa. Upon release of pressure, the high-pressure phase returned to the initial phase. The pressure dependence of the volume of low pressure orthorhombic phase and high-pressure monoclinic phase were described by a second-order Birch-Murnaghan equation of state, which yielded bulk modulus values of B0 = 197(5) and 232(8) GPa, respectively. The results support the empirical suggestion that the oxide spinels have similar bulk modulus around 200 GPa.

High pressure studies of solid methane are performed using both classical simulated annealing and first-principles methods. A series of simulated annealing and geometry optimization reveal a monoclinic P21/b structure with the unit cell containing four methane molecules. The phonon dispersion curves and vibrational density of states indicate that this structure is stable in the pressure range 10–90 GPa. The electronic band structure and density of states show that this structure has not metalized until 90 GPa.

Using the theory of nonlinear interactions between long and short waves, a nonlinear fractal sea surface model is presented for a one dimensional deep sea. Numerical simulation results show that spectra intensity changes at different locations (in both the wave number domain and temporal-frequency domain), and the system obeys the energy conservation principle. Finally, a method to limit the fractal parameters is also presented to ensure that the model system does not become ill-posed.

The electrical conductivity of powdered LiCr0.35Mn0.65O2 is measured under high pressure up to 26.22 GPa in the temperature range 300–413 K by using a diamond anvil cell. It is found that both conductivity and activation enthalpy change discontinuously at 5.36 GPa and 21.66 GPa. In the pressure range 1.10–5.36 GPa, pressure increases the activation enthalpy and reduces the carrier scattering, which finally leads to the conductivity increase. In the pressure ranges 6.32–21.66 GPa and 22.60–26.22 GPa, the activation enthalpy decreases with pressure increasing, which has a positive contribution to electrical conductivity increase. Two pressure-induced structural phase transitions are found by in-situ x-ray diffraction under high pressure, which results in the discontinuous changes of conductivity and activation enthalpy.

High pressure behavior of sodium titanate nanotubes (Na2Ti2O5) is investigated by Raman spectroscopy in a diamond anvil cell (DAC) at room temperature. The two pressure-induced irreversible phase transitions are observed under the given pressure. One occurs at about 4.2 GPa accompanied with a new Raman peak emerging at 834 cm−1 which results from the lattice distortion of the Ti-O network in titanate nanotubes. It can be can be assigned to Ti-O lattice vibrations within lepidocrocite-type (H0.7Ti1.825V0.175O 4H2O)TiO6 octahedral host layers with V being vacancy. The structure of the nanotubes transforms to orthorhombic lepidocrocite structure. Another amorphous phase transition occurs at 16.7 GPa. This phase transition is induced by the collapse of titanate nanotubes. All the Raman bands shift toward higher wavenumbers with a pressure dependence ranging from 1.58–5.6 cm−1/GPa.

In recent years, linear fractal sea surface models have been developed for the sea surface in order to establish an electromagnetic backscattering model. Unfortunately, the sea surface is always nonlinear, particularly at high sea states. We present a nonlinear fractal sea surface model and derive an electromagnetic backscattering model. Using this model, we numerically calculate the normalized radar cross section (NRCS) of a nonlinear sea surface. Comparing the averaged NRCS between linear and nonlinear fractal models, we show that the NRCS of a linear fractal sea surface underestimates the NRCS of the real sea surface, especially for sea states with high fractal dimensions, and for dominant ocean surface gravity waves that are either very short or extremely long.

A numerical method for extracting parameters of extreme sea wave and calculating its dispersion relation is presented. The nonlinear sea surface can be regarded as waves whose wave numbers and frequencies change with temporal and spatial points. At every point, the height of sea surface can be interpolated by the value of an extending sine wave whose parameters （such as wave numbers and frequencies） are constant. From the first order and the second order derivative of extreme wave, we can extract wave numbers, frequencies, and amplitudes of the extreme wave. The numerical amplitude results show that this method is valid. Comparing values of ω2/k with g, we can find that the nonlinear area does not lie in the area of extreme waves, but lies very closely to both sides of them. The corresponding wave heights in these areas are lower than that in the linear dispersion area. Compared with wavelet and Hilbert transform analysis method, our method has two advantages: Firstly, it saves much buffer capacity and CPU time. Secondly, it can supply disperse relationship of systems which other methods cannot supply. The disadvantage of this method is that, in the area of engineering application, it is only applicable to systems with coexisting temporal series data and spatial data.

The potential that a hydrogen atom experiences in a metallic niobium crystal is calculated using the pseudopotential plane-wave method based on density functional theory. The quantum states of the hydrogen atom in such a potential are obtained by solving Schrdinger equation directly. The ground state and the first excited state are shown to be local, while the others are delocalized. A hydrogen atom in high excited states may move on a 4T or 6T ring.

The total energies and electronic structures of differently configured Nb2H are calculated using pseudopotential plane wave method based on density functional theory and generalized gradient approximation. The results show that hydrogen atom favors tetrahedral (T) sites (T-wells) rather than octahedral (O) ones. There exist lower energy paths along adjacent T-T sites and saddle structures at the midpoint of them. When H is at T-site or along the T-T path, its 1s level is less broadened and the 4d, 5s bands of Nb extend downward from the metallic band area, forming an ionic band (sharp peak) separated by a gap of about 1 eV from the metallic valence bands, showing that the hydrogen atom captures one valence electron to form an anion. This low-lying ionic band loses its T-site hybridization features when H moves from T to O site, where the 1s band of H is widely broadened, extending into the metallic valence bands. The band structure changes only slightly when the hydrogen atom moves from one T site to a neighbor one along the lower energy path, keeping the T-configuration features. The calculated phonon spectra of H are dispersive only near special q-points for the system with H at a T site, showing that the hydrogen atom is probably vibraing locally and weakly interacts with other hydrogen atoms. The behavior of H at a trapping site plays an important role in bonding of the surrounding Nb atoms.

The C60@SWNT (peapod) samples were prepared by the vapor diffusion method. Polymerization of C60 molecules in single walled carbon nanotubes (SWNTs) under high pressure and simultaneous irradiation of UV laser (325 nm) has been carried out for the first time by using diamond anvil cell. Raman spectra of the peapod samples decompressed from high pressure indicated that C60 molecules form one-dimensional orthorhombic polymer in SWNTs under UV laser irradiation at a high pressure of 21.5GPa, which is lower than that for the polymerization of samples induced by high pressure only. The polymerization is an irreversible phase transition in the peapod.

The pressure effects on the elastic properties of lithium doped by hydrogen are studied using first-principles methods based on density functional theory. A supercell including 16 Li atoms in hcp lattice is constructed with a hydrogen atom interstitially doped in. The supercell is fully relaxed at 0K. The elastic properties of the stable lattice are studied. The result shows that the bulk modulus increases after hydrogen atom is added. The elastic constants C 11 , C 33 , C 66 and C 12 are larger than those of pure Li，while the shear modulus C 44 is smaller. The elastic constants increase with external pressure, with C 11 , C 33 and C 66 larger than those of pure Li while C 12 being smaller. C 13 is abnormally lower than that of pure Li within the pressure range from 2GPa to 4GPa, while C 44 and C 13 are greater at higher pressure area. The discrepancy of shear modulus between the doped and the pure system is enhanced by external pressure. The analysis of anisotropy Δ W shows that the doped system maintains isotropic under external pressure as does pure Li.

The phase transformation of amorphous bismuth titanate fabricated by sol-gel method was investigated by X-ray diffraction (XRD), transmissions electron microscopy (TEM) and differential thermal analysis (DTA). The experimental results show that the four-step crystallizations were present on heating. The metastable phases Bi 2 O 3 and TiO 2 were formed firstly at 433℃, and Bi 2 Ti 4 O 11 phase was subsequently formed at 488℃ by the reaction between Bi 2 O 3 and TiO 2 . Sequential reaction between Bi 2 Ti 4 O 11 and Bi 2 O 3 resultedin the formation of Bi 4 Ti 3 O 12 phase with tetragonal structure at about 644℃, and stable Bi 4 Ti 3 O 12 phase with orthorhombic structure was finally formed at about 830℃.

Face-center cubic metal materials including austenite stainless steel, aluminum single crystal and multi-grained pure aluminum were irradiated by a high-current pulsed electron beam (HCPEB) source in different processes. The deformed microstructures were observed by using scanning electron microscopy and transmiss ion electron microscopy. The relationship between stress characteristic and the microstructures has been analyzed. The current numerical simulations of the ther mal-mechanical process of HCPEB treatment were also investigated by comparing w ith the present experimental results. The present experimental results suggest t hat the value of the stress induced by HCPEB lies between 102—103MPa. The behavior of the stress propagation is closely related to the crystal structure of the material. This stress leads to the modification of the properties and the microstructures of the irradiated material in regions of greater depth.

The Raman spectra of Pb1-xBaxTiO3(x=0,0. 2,0. 3) have been measured. Experimental results show that there is an obvious effect of small size of crystal in the system.

The specimens of single-crystal aluminum were irradiated with high current pulsed electron beam (HCPEB). The vacancy cluster defect microstructure has been investigated by using transmission electron microscopy (TEM). The results show that three types of vacancy clusters including dislocation loop, void and even stacking fault tetrahedron (SFT), which are not normally formed in metals with high SFT formation energy, can be formed in single-crystal aluminum specimens irradiated with HCPEB. The nucleation process of three types of vacancy clusters do not appear at the same time. There is a close relationship between the three types of vacancy clusters. Based on the experimental results, a possible mechanism of SFT formation and evolution was presented.

We investigate, by first-principles calculations, the pressure dependence of formation enthalpies and defective geometry and bulk modulus of boron-related impurities (VB, CB, NB, and OB) with different charged states in cubic boron nitride (c-BN) using a supercell approach. It is found that the nitrogen atoms surrounding the defect relax inward in the case of CB, while the nitrogen atoms relax outward in the other cases. These boron-related impurities become much more stable and have larger concentration with increasing pressure. The impurity CB+1 is found to have the lowest formation enthalpy, make the material exhibit semiconductor characters and have the bulk modulus higher than ideal c-BN and than those in the cases of other impurities. Our results suggest that the hardness of c-BN may be strengthened when a carbon atom substitutes at a B site.