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Nonlinear Electrical Behaviour of Composite SnO2-Zn2SnO4 System

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Chinese Physics Letters 2005年第3期22卷 750-753页

作者：臧国忠王矜春陈洪存苏文斌王春明亓鹏 schoolofphysicsandmicroelectronics ShandongUniversityJinan250100

We have found a new composite SnO2-Zn2SnO4 varistor material and the effectof different content ratios of SnO2 to Zn2SnO4 on this system is investigated. The lowest breakdownvoltage (E-B = 6.4 V/mm) and the highest relative dielectric constant (epsilon(r) = 1.54 X 10(4))with higher nonlinear coefficient (a = 4.5) is obtained when the ratio of SnO2 to ZnO equals 100/*** disappear of the Zn2SnO4 peak in x-ray diffraction (XRD) spectra of the SnO2-P2.5mol%ZnO sampleand the electric insulation behaviour of the samples with 2.5mol% ZnO and 200mol% ZnO indicate that2.5mol% ZnO can be dissolved into SnO2 lattices and some reaction contributing to nonlinearelectrical behaviour should occur between SnO2 and Zn2SnO4. The role of oxygen on the grain boundaryis confirmed by the degradation of nonlinear electrical properties and the increase of relativedielectric constant of the samples annealed in nitrogen-rich atmosphere.

关键词： METAL-OXIDE VARISTORS ZINC-OXIDE CERAMICS SNO2 OXYGEN

Structure Properties of MgxZn1-xO Films Deposited at Low Temperature

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Chinese Physics Letters 2005年第4期22卷 995-997页

作者：张锡健马洪磊王卿璞马谨宗福建肖洪地计峰 schoolofphysicsandmicroelectronics ShandongUniversityJinan250100

MgxZn1−xO films (x = 0.23) have been prepared on silicon substrates by radio-frequency magnetron sputtering at 80 degrees C. The structure properties of MgxZn1−xO films are studied using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy and Raman spectra. The analysis of XRD and HRTEM indicates that the MgxZn1−xO films have hexagonal wurtzite single-phase structures and a preferred orientation with the c axis perpendicular to the substrates. Raman spectra of ZnO and MgxZn1−xO films reveal that the MgxZn1−xO films have not only the hexagonal wurtzite structure but also higher crystalline quality than ZnO films.

关键词：结构性质 MgxZn1-xO 薄膜沉降低温条件

A New Model Potential Acting on the Excited Electron Within Molecules： Application to Calculate the Recurrence Spectra of Excited H2 Molecules in Strong External Fields

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Chinese Physics Letters 2004年第7期21卷 1191-1194页

作者： WANGDe-Hua DINGShi-Liang schoolofphysicsandmicroelectronics ShandongUniversityJinan250100

By using the molecular orbit theory, we give a new model potential acting on the excited electron within a molecule. The potential is the total interaction energy of this electron with all the nuclei and other electrons. We find that the introduction of a new model potential results in an extreme increase of the number of closed orbits as compared to the hydrogen atom. Making use of the molecular closed-orbit theory (MCOT) and the new model potential, we calculate the recurrence spectra of H2 molecules in parallel electric and magnetic fields for different quantum defects. The modulations in the spectra can be analysed in terms of the scattering of the excited electron on the molecular core. Our results are in good agreement with the quantum results.

关键词： Molecules

Ab Initio Calculations for the BaTiO3 （001） Surface Structure

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Chinese Physics Letters 2004年第5期21卷 825-828页

作者：薛旭艳王春雷钟维烈 schoolofphysicsandmicroelectronics StateKeyLaboratoryofCrystalMaterialsShandongUniversityJinan250100

The ab initio method within the local density approximation is applied to calculate cubic BaTiO3 (001) surface relaxation and rumpling for two different terminations (BaO and TiO2). Our calculations demonstrate that cubic perovskite BaTiO3 crystals possess surface polarization, accompanied by the presence of the relevant electric field. We analyse their electronic structures (band structure, density of states and the electronic density redistribution withm emphasis on the covalency effects). The results are also compared with that of the previous ab initio calculations. Considerable increases of Ti-O chemical bond covalency nearby the surface have been observed. The band gap reduces especially for the TiO2 termination.

关键词： Surfaces interfaces and thin films

Effects of Er2O3 on Electrical Properties of the SnO2·CoO·Ta2O5 Varistor System

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Chinese Physics Letters 2004年第4期21卷 716-719页

作者：王春明王矜奉陈洪存苏文斌臧国忠亓鹏 schoolofphysicsandmicroelectronics NationalKeyLaboratoryofCrystalMaterialsShandongUniversityJinan250100

We investigate the effects of Er2O3 on electrical properties of the ***2O5 varistor system sintered at 1400 degrees C. It is found that all the samples have excellent nonlinear electrical characteristics and the sample with 0.50mol% Er2O3 has the best nonlinear electrical property and the highest nonlinear coefficient (α = 43.7). The high nonlinear coefficient value obtained in the system indicates that the SnO2-based varistor is a candidate for ZnO-based varistors in commercial applications. Er2O3 additive can significantly affect the average grain size. With increasing Er2O3 concentration from 0.10mol% to 1.00mol%, the average grain size decreases from 21.2μm to 10.6μm, the breakdown electrical field increases from 208V/mm to 459V/mm, and the relative electrical permittivity decreases from 2440 to 1210. The reason that the grain size decreases with increasing Er2O3 concentration is explained. Also, we present a modified defect barrier model to illustrate the grain-boundary barrier formation of Er2O3-doped SnO2 based varistors.

关键词： Varistors

Size Driven Ferroelectric—paraelectric Phase Transition from the Surface Energy Viewpoint

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Chinese Physics Letters 2003年第7期20卷 1134-1136页

作者：钟维烈王渊旭张沛霖 schoolofphysicsandmicroelectronics StateKeylaboratoryofCrystalmaterialsShandonguniversityJi'nan250100

The size driven ferroelectric-paraelectric phase transition in a ferroelectric of small size is studied within the framework of Landau phase transition theory. The transition is a consequence of the competition between decreasing the volume free energy by polarization and increasing the surface energy of the ferroelectric phase, which has a surface energy density higher than that in the paraelectric phase. A simple expression for the ferroelectric critical size as a function of the Landau free energy coefficients and the surface energy density is derived.

关键词： Comment Phase transtormations Free energy Surface energy Polarization energy density small size

Vibrational Modes Analysis of Poly （Vinylidene Fluoride—Trifluoroethylene）

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Chinese Physics Letters 2003年第6期20卷 921-923页

作者： LIJi-Chao WANGChun-Lei ZHONGWei-Lie LIZheng-Fa schoolofphysicsandmicroelectronics StateKeyLaboratoryofCrystalMaterialsShandongUniversityJi'nan250100

The ground state geometry and vibrational modes of poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] molecular chains have been investigated by ab initio molecular orbital calculation. The gauche bonds in P(VDF-TrFE) are introduced by TrFE monomers. The vibrational modes are localized within all-trans segments. These results cause the infrared absorption weaker and diffused, and may be responsible for dielectric relaxation of the copolymers.

关键词： Ground state Copolymers DIELECTRIC RELAXATION Vibrations modes vinylidene fluoride TRANS Vinylidene fluoride trifluoroethylene copolymers vinylidene

Transition Between Solid-like and Liquid-like States in Soft Silica Suspensions

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Chemical Research in Chinese Universities 2004年第6期20卷 771-773页

作者： ANKang HUJi-fan SUNDe-jun QINHong-wei ZHANGJie HANTao ZHANGLing schoolofphysicsandmicroelectronics ShandongUniversityJinan250100P.R.China

The influences of silica volume fraction, electrolyte concentration and pH value upon the stress dependence of elastic modulus G′and viscous modulus G″ were investigated. The results show that the suspension transforms from a liquid-like state to a solid-like state with increasing the volume fraction of silica. Such a solid-like state can be transformed back into a liquid-like state under the application of a larger stress. At the higher volume fraction, the larger critical stress is required to induce the transition from solid-like to liquid-like state. As the electrolyte concentration decreases or pH value increases, the inter-particle force increases, which causes the state transition to occur at a higher stress.

关键词： Soft matter State transition Suspension

Polaronic Tunnelling in Organic Triblock Copolymers

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Chinese Physics Letters 2005年第1期22卷 178-181页

作者：刘德胜张大成解士杰梅良模 schoolofphysicsandmicroelectronics ShandongUniversityJinan250100//DepartmentofPhysicsJiningNormalUniversityJining272025//NationalKeyLaboratoryofCrystalMaterialsShandongUniversityJinan250100 schoolofphysicsandmicroelectronics ShandongUniversityJinan250100//NationalKeyLaboratoryofCrystalMaterialsShandongUniversityJinan250100

Polaron tunnelling is studied in xPA/nPPP/xPA (PA for polyacetylene and PPP poly (p-phenylene)) triblock copolymer, which has a well–barrier–well structure. An extended tight-binding Hamiltonian including external electric field is adopted. Without electric field, the injected electrons would not extend over the whole copolymer chain but instead be confined in the segments of PA. This is different from the behaviour of the traditional semiconductors. It is found that the polaron can transfer to the potential barrier-PPP segment when the applied electric field reaches a certain value. The critical polaron tunnelling electric fields depend upon the lengths of PPP segments.

关键词：极化隧道效应共聚物组织摩擦聚乙炔电场