Small-size ZnO/MgO quantum systems with zinc oxide nanoparticles of controlled size

A method is proposed for the preparation of nanosized ZnO/MgO systems by the deposition of previously formed zinc oxide nanoparticles onto a support from a colloidal solution and for determination of the size of the deposited ZnO particles from the electronic spectra. The morphology of composites containing zinc oxide nanoparticles was investigated by electronic spectroscopy and transmission electron microscopy. The possibility of synthesizing solid-phase ZnO/MgO quantum systems with controllable size characteristics was demonstrated. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 3, pp. 183–188, May–June, 2007.     

Application of molecular models to electronic structure calculations of defects in oxide crystals. I. Parametrization of the modified INDO method

A modified calculation scheme of the INDO method is applied for calculating the electronic structure of perfect and imperfect oxide crystals. In order to obtain a flexible scheme permitting reliable calculation of both the electronic structure and the defect conformations, the INDO parameters for H, Li, Mg, Si, O are fitted directly to reproduce one-electron energies as well as the vicinity of the potential energy curve minima for a series of diatomic molecules and the electronic structure of MgO and -crystoballite form of SiO₂. The method is tested on the Li₂SiO₃ crystal calculated within the framework of the large unit cell model.     

Effect of MgO nanoparticles on ionic conductivity and electrochemical properties of nanocomposite polymer electrolyte

This paper analyzes the comparison between the performances and morphologies of the PMMA gel and composite electrolyte membrane with nanosized MgO particles. These polymer electrolytes were studied in detailed using XRD, DSC, SEM and AC impedance analysis. The conductivity enhancement has been attributed to the addition of ceramic filler that yields a significant increase of surface to volume ratio related to the decrease in glass transition temperature values in the composite polymer electrolyte. Good interfacial stability at the electrode/electrolyte interface resulted on account of the improved ion dissociation by ceramic filler and a rise in the room temperature conductivity (8.14 × 10⁻³ S cm⁻¹) due to the iono-covalent or Lewis acid–base bonds to the ions and ether oxygen base groups was also observed. Further enhancement of conductivity has been observed on MgO surface, as Lewis-acidic sites interact with both PMMA and ClO₄⁻ ions. The percentage of swelling was found to increase with increasing soaking periods upto 12 h. Beyond that soaking period, it was found that there was a negligible increase in the % of swelling.     

Electrical and Optical Properties of MgO Thin Film Prepared by Sol-Gel Technique

MgO thin films with either (111) or (200) preferential orientation have been prepared on (100) Si substrates by sol-gel method after a heat-treatment at 800°C. The obtained (111) preferentially oriented MgO film has a dielectric constant of 7.0 with a loss factor of 5% and a dielectric strength higher than 8 × 10⁵ V/cm. The optical refractive index, which depends on the film thickness, is 1.71 when the film thickness is 260 nm. The surface structure of the Si substrate is believed to affect the preferential orientation of the sol-gel derived MgO film. Specifically, the microstructures at the interface indicate an interdiffusion of Mg, O, and Si between the film and the substrate.     

O2在具有氧和镁缺陷MgO(001)表面的吸附

在密度泛函理论的框架下，采用嵌入点电荷簇模型研究了O2在具有氧缺陷和镁缺陷MgO(001)表面上的吸附.用电荷自洽的方法确定了点电荷的值.计算结果表明，O2倾向吸附在具有氧缺陷的MgO(001)表面上.通过和我们近期研究过的O2在低配位的边、角上吸附结果相比较，发现具有氧缺陷的MgO(001)表面更加有利于O2的吸附和解离. Mülliken电荷分析表明，电荷由底物向吸附的O2反键轨道上转移是导致O2键强削弱的主要原因.势能曲线表明，O2在具有氧缺陷的MgO(001)表面上发生解离所需要克服的能垒比在角阳离子端发生解离所需克服的能垒有大幅度降低.     

Surface basicity of alkali metal-doped MgO by a new evaluation

A new parameter, ( v)^–1 is proposed for evaluating the surface basicity of alkali metal-doped MgO from a positive correlation with acetone/propene ratio in the decomposition of 2-propanol.     

高温煅烧Mo改性的Fe／MgO催化剂用于制备管径分布均一的单壁碳纳米管

研究了在以甲烷化学气相沉积法制备单壁碳纳米管的过程中高温煅烧预处理(900℃煅烧10h)对Mo改性Fe/MgO催化剂的作用.发现这种预处理有利于Fe在催化剂中的稳定和分散,从而制备出管径均一的单壁碳纳米管.采用能谱元素分析、高分辨透射电镜、X射线衍射、比表面积测量、拉曼光谱和热重分析对样品进行了表征.结果表明,在碳纳米管生长的过程中,铁元素在催化剂表面富集,单壁碳纳米管生长于富集铁的纳米颗粒上,并存在碳管直径与铁颗粒尺寸的依赖关系.Mo存在时可煅烧形成FeMoO4复合氧化物,后者比MgFe2O4相更加稳定.Mo/Fe比例对提高单壁碳纳米管的生长密度、纯度与管径均一性等均有明显影响.上述研究对进一步精确控制制备单壁碳纳米管有重要意义.     

配合物Mg(OEt)(acac)的电化学合成

在溴化四丁基铵[(Bu4N)Br]的乙醇(EtOH)和乙酰丙酮(acacH)混合溶液中,电流强度0.2A,电解镁片6 h制得乙氧基镁配合物Mg(OEt)(acac).Bu4NBr浓度在40 mmol·L-1～50 mmol·L-1时,电流效率超过90%.在Mg(OEt)(acac)浓度210 mmol·L-1,pH 8.0,于40℃水解12 h的条件下,Mgo干凝胶收率超过87%.Mg(OEt)(acac)和Mg0干凝胶的结构经1H NMR,IR,XRD和拉曼光谱表征.     

Phonon States and Dispersive Spectra of Polar Optical Phonons in Quasi-One-Dimensional Nanowires of Wurtzite ZnO and Zinc-Blend MgO Semiconductors

Within the framework of the macroscopic dielectric continuum model and Loudon's uniaxial crystal model, the phonon modes of a wurtzite/zinc-blende one-dimensional (1D) cylindrical nanowire (NW) are derived and studied. The analytical phonon states of phonon modes are given. It is found that there exist two types of polar phonon modes, i.e. interface optical (IO) phonon modes and the quasi-confined (QC) phonon modes existing in 1D wurtzite/zinc-blende NWs. Via the standard procedure of field quantization, the Fröhlich electron-phonon interaction Hamiltonians are obtained. Numerical calculations of dispersive behavior of these phonon modes on a wurtzite/zinc-blende ZnO/MgO NW are performed. The frequency ranges of the IO and QC phonon modes of the ZnO/MgO NWs are analyzed and discussed. It is found that the IO modes only exist in one frequency range, while QC modes may appear in three frequency ranges. The dispersive properties of the IO and QC modes on the free wave-number k_z and the azimuthal quantum number m arediscussed. The analytical Hamiltonians of electron-phonon interaction obtained here are quite useful for further investigating phonon influence on optoelectronics properties of wurtzite/zinc-blende 1D NW structures.     

加压条件下MgO/BaCO_3催化剂在甲烷氧化偶联反应中的性能研究(英文)

在加压条件下（0.1~1.1MPa）考察了MgO／BaCO_3催化剂在甲烷氧化偶联反应中的性能,以及加压后该催化剂的失活。XRD谱图表明,在加压失活的MgO／BaCO_3催化剂表面有部分MgCO_3牛成,这是由于部分活性相MgO发生了转变：XPS表征结果表明,在加压失活后的MgO／BaCO_3催化剂中B3CO_3向表面富积,致使催化剂的表面活性相MgO的浓度相对降低和催化剂表面积降低。另外,在加压失活后的MgO／B3CO_3催化剂上表面活性氧物种的离子浓度大大降低,表面晶格氧的流动性及晶格氧参与甲烷转化的能力也大大减弱;另外,由于该失活催化剂表面结构的变化,由MgO和BaCO_3共同作用形成的强碱中心也消失了。