Lin Li-Bin

Investigation on lattice constants of Mg-Al spinels

Mg-Al spinel is the most typical material in the family of chemical compounds with spinel crystalline structure that exhibits many applications [1, 2]. In general, it can be noted as MgO-n·Al2O3. MgAl2O4 spinel is an fcc structure of oxygen ions with a lattice parameter of 0.808 nm. There are eight molecules in its unit cell, in which there are 64 tetrahedral symmetry sites and 32 octahedral ones. In the perfect case, magnesium ions occupy 8 tetrahedral positions and aluminum ions occupy 16 octahedral sites [3]. In many cases, this MgO-n·Al2O3 compound is nonstoichiometric, n is not equal to 1. Form 1 up to 7.3, the excess Al3+ ions occupying tetrahedral sites, substitute for Mg2+ ions [4]. This causes a proportional decrease of lattice parameter with the amount of excess Al3+ due to a smaller diameter of Al3+ than that of Mg2+. In the present paper, we show the result of the unit cell parameters of Mg-Al spinels solid solutions with XRD and provide a formula for calculating the lattice parameter of such Mg-Al spinel compounds, which has a good physical meaning compared with that given by Sigalovsky et al. [5]. In our experiments ultra-fine powders of Mg-Al spinel were prepared with a method of high temperature solid reaction. Reagent grade AlNH4(SO4)2·12H2O and MgSO4·7H2O were mixed based on different n in de-ionized water. These solutions were calcimined at 1080 ◦C for 4–5 h to obtain a single spinel phase powder with being high pure, good disperse and homogeneous. The obtained powders were measured by XRD using Cu-Kα radiation on a D/max rA diffractometer. The XRD patterns of the obtained powder samples are given in Fig. 1. The stoichiometric spinel XRD pattern (a pattern labelled n= 1.0) is the same as the standard powder XRD pattern [6]. For the non-stoichiometric spinel samples, the peaks shift to the direction in higher values of 2θ as n increases. That means the distance of (hkl) plane dhkl became smaller according to the following expression:

Ti ion valence variation induced by ionizing radiation at TiO2/Si interface

Abstract Titanium oxide films are prepared on silicon substrates by the DC reactive sputtering method. The TiO 2 /Si structures with different TiO 2 film thickness are irradiated by electron beams and γ-rays. It is found after irradiation that the shift of flat-band voltage Δ V FB of MOS structures is very small. There is no evident distortion in the HF C – V curves in comparison with pre irradiation cases. By the XPS analysis, it is found that, after irradiation, the valence of the Ti ion varies; the Ti 3+ ion increases and the Ti 4+ ion clearly decreases at the TiO 2 /Si interface. The variation comes mainly from the transition layer between the titanium oxide film and silicon substrate. The mechanism has been discussed in detail.

The quantum nonthermal effect of a nonstationary Kerr-Newman black hole and the average range of the effective particles

We have found that the nonthermal radiation of a nonstationary Kerr-Newman black hole is affected by interstellar materials. In particular, the interstellar gas deeply influences the average range of nonthermal radiation particles, while the average range depends on the maximum energy of the radiation and the energy extent of the radiation.

DEFECTS IN SAPPHIRE:MN INDUCED BY NEUTRON IRRADIATION

Abstract After neutron irradiation, some impurity ions changed their valence states, as well as some new defects such as vacancies, interstitials and the clusters were produced. The thermoluminescence (TL) with electron paramagnetic resonance (EPR), positron annihilation technique (PAT) measurements were used to determine the defects in Sapphire: Mn irradiated by fast neutron of 2 MeV average energy and thermal neutron of 0.023 eV. The results of TL show that before irradiation peaks of 171°C, 259°C, 320°C, 350.2°C and 408°C all belong to the intrinsic crystal, the peak of 196°C is induced by impurity ion of Mn. After neutron irradiation, the peaks all moved to higher temperature, but got different shifts and produced a new peak of 154°C. The shift of peak 196°C is about 30°C. It is explained that Mn ion aggregated with a nearest defect and formed a cluster, which corresponding to EPR results might be Mn 2+ –F cluster and the nearest defect might be F type center. The mechanism of other shifts and another peak are also discussed in the paper.

New kinds of Dirac energy levels and their crossing regions

In the space-time of a non-Kerr-Newman black hole, the Dirac energy levels and their crossing regions are investigated. Near the event horizon of the black hole there are crossing Dirac energy levels, which lead to the occurrence of non-thermal radiation.

Soliton-like pulse timing jitter in dispersion-managed systems

In this paper, the timing jitter in dispersion-managed soliton-like systems with the Gaussian pulse is studied by using two methods. Firstly, the derivation of the dynamic equations for the evolution of soliton-like parameters and the timing jitter expressions for the dispersion-managed soliton-like systems are carried out by the perturbed variational method. By analysing and simulating these timing jitter expressions, one can find that the timing jitter is induced by the amplified spontaneous emission noise and the frequency shift, etc. Nonlinear gain can suppress the timing jitter. The chirp sign and the filters action have also effects on the total timing jitter. Secondly, the timing jitter is calculated and analysed by using the moment method. The results of the two methods prove to be consistent with each other.

Electron capture in fp shell at presupernova stage

The electron capture of neutron-rlch nuclei in fp shell in massive stars at presupernova stage is discussed based on the nuclear shell model. The Gamow-Teller resonance transition strength is modified by introducing a Gaussian function. As a result, the electron capture rate in high density is evidently larger than the previous results given by some authors.The electron capture of neutron-rich nuclei in fp shell in massive stars at presupernova stage is discussed based on the nuclear shell model. The Gamow-Teller resonance transition strength is modified by introducing a Gaussian function. As a result, the electron capture rate in high density is evidently larger than the previous results given by some authors.

Variation of morphology and color of VO2 thin films induced by excimer laser

Abstract The samples of VO 2 thin films are irradiated by excimer laser with a wavelength of 308 nm under different output energy. Precipitation and recrystallization phenomenon on the surface are observed in the irradiated samples with lower and higher irradiation energy of laser respectively. Hence, the obvious variation of morphology is observed in irradiated samples with different irradiation energy. Precipitation process just slightly brings down the intensity of X-ray diffraction (XRD) peaks but recrystallization process can change the intensity and width of XRD peaks of samples. The results of laser Raman spectroscopy (LRS) and scanning electron miscroscopy (SEM) analysis indicate that the size of crystalline grain increases after recrystallization. The other optical properties of samples are also measured before and after irradiation.

Electron and neutron irradiation effects of Al2O3:V

Abstract Samples of Al2O3:V before and after electron and neutron irradiation were studied by optical absorption spectra, emission spectra and positron annihilation lifetime spectra. It was shown that a part of V4+ ions changed into V3+ ions by electron irradiation; and F2+ and F2 centers were produced in Al2O3:V crystals by neutron irradiation. F2 centers in Al2O3:V can emit continuous luminescence bands in the range of 460–560 nm which can be expected to be used for solid tunable lasers.

Non-thermal radiation from a non-Kerr-Newman black hole

In the spacetime of a charged spinning black hole, the distribution of particle energy levels has been studied. Near the event horizon of such a black hole a crossing of the particle energy levels exists, which leads to the occurrence of non-thermal radiation of the black hole. This quantum effect is non-thermal and also different from those of the Kerr and Kerr-Newman black holes.