Spin relaxation and ultra-slow Li motion in an aluminosilicate glass ceramic

The ion dynamics in a lithium aluminosilicate glass ceramic was studied using stimulated-echo 7Li-NMR. For temperatures 300 K相似文献   

Crystallization and the electrical conductivity of vanadate glass

The common formula of the minerals franckeite, cylindrite and potosiite is known to be w PbS × SnS₂ y FeS z Sb₂S₃. The tin Mössbauer spectra showed the existence of two Sn(IV) and two Sn(II) species, and the iron spectra one high spin Fe(II) and two Fe(III) species. For antimony, only one Sb(III) phase is present, except in potosiite where also 20 % of Sb(V) were found. The mineralogical relationships within this group were confirmed by the Mössbauer spectroscopical results.     

Abrupt change of ionic conductivity induced by an electric field

A theory of abrupt disordering of one of ionic crystal sublattices in an external electric field is developed. It is shown that it is possible to transfer a crystal into a high-conductivity state without heating by means of a field-induced phase transition.     

Low-temperature spin-lattice relaxation of8Li in the glass Li2O·2SiO2

Nuclear spin-lattice relaxation in Li₂0·2Si0₂ glass below 200 K has been studied using the asymmetric Β-decay radiation of polarized⁸Li (T_1/2=0.Bs) nuclei produced by capture of polarized neutrons. Transients of the⁸Li polarization follow an exp(?√E/T₁) law. The dependence of the spin-lattice relaxation rate ⊥_¯1 ¹ on temperature T and magnetic field B can roughly be described by T_¯1 ¹～T/B. The interpretation is based on the assumption that for⁸Li, contrary to⁷Li in the same glass, spin-diffusion is absent and that each probe nucleus is coupled by quadrupolar interaction to an individual distribution of nearby centres typical of glasses. The fluctuation of these centres causing relaxation may be induced by either a multi-phonon or a thermally activated motional process.     

Compositional dependence of the electrical conductivity of vanadium phosphate glass

The bulk resistivities of vanadium phosphate glasses in the compositional range from 65 to 85 mole % V₂O₅ were measured and fitted as a function of composition to the equation for conductivity as proposed by Mott and later modified by Sayer and Mansingh for n, the number of unoccupied mearest sites surrounding the final hopping site of the small polaron. The fit to the experimental data was found to be best if the number n is chosen to be proportional to the total number of V⁵⁺ sites in the glass. Also n is found to be non-integer and can be regarded as the effective number of unoccupied sites surrounding the final site in the sense of eqn (24) developed in this paper. Values for n ranged from 0.2 to 5 for different compositions of the glass. A model for the structure of vanadium phosphate glass is proposed to explain the data.     

High ionic conductivity of hydrated Li0.5FeOCl

Iron oxychloride has been lithiated by the reaction with n-butyllithium and thereafter exposed to air. Lithium intercalation increases several orders of magnitude of the electrical conductivity of the pristine material although the intercalate remains a semiconductor. This phase, after being exposed to atmospheric humidity becomes an ionic conductor, with a conductivity comparable to that of some molten salts, and does not show electronic conduction in the whole range of temperatures of measurement (150–300 K), a strong non-Arrhenius behaviour being observed. Impedance spectroscopy and NMR techniques, among others, have been used to follow this behaviour.     

硅酸锂球床等效导热率研究

基于计算流体力学(CFD)方法,结合国际热核实验反应堆(ITER)中实际使用的设计参数,对硅酸锂球床的传热特性进行了流固耦合传热分析,给出了多种工况下的热工水力结果。同时将用CFD得到的球床区域等效导热系数与相关实验的结果进行了比较。     

Ac dielectric losses and electrical conductivity of vanadium-borate glass

The conductivity and capacitance of bulk and thin-film metal-glass-metal structures with the glass based on the composition: 32.56% V₂O₅, 46.18% B₂O₃, and 21.26% CaO (mole %) are measured in the frequency interval 2·10²–2·10⁴ Hz and the temperature interval 300–500°K. The frequency-temperature dependences of the real and imaginary parts of the complex dielectric constant calculated from the results of the measurements indicate the presence of the process of relaxation polarization in the glass under investigation. The parameters of the relaxation process are determined. It is proposed that the presence of the relaxation component of the conductivity and losses is due to localization of small-radius polarons (SRP) in the vicinity of positively charged defect centers (bound SRP).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 85–89.     

Predissociation induced by ungerade-gerade symmetry breaking in 6Li7Li molecule

In the recent sub-Doppler experiment on the B1Pi(u) state of the Li2 molecule by Bouloufa et al. [J. Chem. Phys. 111, 1926 (1999)], where the dissociation of vibrational levels due to the tunneling through the potential barrier was investigated, several vibrational levels with abnormally large dissociated rates were observed in the case of the 6Li7Li isotopomer. This dynamical effect cannot be explained by tunneling as in the case of 6Li2 or 7Li2. A simple model of coupling between B1Pi(u) and 1(1)Pi(g) states involving the u-g symmetry breaking for 6Li7Li is proposed. Rates of the B1Pi(u) predissociated levels due to this coupling are calculated. A good agreement with the experiment is found.     

飞秒激光诱导Li2O-Nb2O5-SiO2玻璃析晶拉曼谱研究

通过使用波长 800nm、重复频率 250kHz的飞秒激光脉冲聚焦进Li2O-Nb2O5-SiO2组分的玻璃内部,空间选择性诱导出铌酸锂微晶.为了进一步地研究辐照区域晶体的生长机制,使用显微拉曼光谱仪分析了玻璃样品辐照区域不同位置的结构变化.研究表明,在飞秒激光辐照一段时间后的聚焦区域,由于非线性效应和热累积效应形成了一个高温辐射梯度场,在激光辐照中心区域超过玻璃的析晶温度而促使玻璃熔融析晶.     

Effect of Li doping on the critical temperature and glass formation in the Bi-Sr-Ca-Cu-O system

A study has been made of the glass-forming ability, structure, and superconducting properties of Bi_2.2Sr_1.8Ca_1.05Cu_2.15Li_xO_y and Bi_2.2Sr_1.8Ca_1.05Cu_2.15−x Li_xO_y (x=0;0.3;0.5;0.7). The compounds were melted by rf at T=1300–1500 °C. Rapid quenching produces glassy alloys whose glass-forming ability is the highest when lithium is substituted for copper. Glass annealing at 700–800 °C results in the formation of the HTSC phase 2212 with a critical temperature of up to 91 K. In lithium-doped samples the HTSC phase forms at lower temperatures and shorter anneals and it depends on the cooling rate following the anneal. The composition and properties of the 2212 phase depend nonmonotonically on the anneal time. The lattice parameter C of the 2212 phase increases with increasing lithium content. Fiz. Tverd. Tela (St. Petersburg) 41, 18–21 (January 1999)     

DC electrical conductivity of vanadium-borate glass in weak and strong electric fields

The results of an investigation of the temperature and field dependences of the electrical conductivity of vanadium-borate glass with the composition 32.56% V₂O₅, 46.18% B₂O₃, and 21.26% CaO (mole %) are discussed. The measurements were carried out on metal-glass-metal sandwich structures in the temperature interval 200–500°K with electric field intensities up to 10⁸ V/m. It is shown that the experimental data for T 350°K can be described within the framework of the percolation conductivity theory with a variable jump length, which permits explaining the value of the critical field and the temperature dependence of the slope of the current-voltage characteristics (CVC). It is proposed that for T > 350°K the essential role in forming the CVC is played by small-radius polarons (SMP) localized in the vicinity of positively charged defect centers (bound SRP).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 90–94, May, 1982.     

Fabrication and ionic conductivity of Li2SiO3 thin film

Lithium meta-silicate (LSO) thin film was fabricated on various insulating substrate by a pulsed laser deposition (PLD) method. By X-ray diffraction measurement, as-prepared thin film is found to be amorphous structure. Temperature dependence of the ionic conductivity was measured at the temperature range from 500 to 700 K. It was found that the ionic conductivity depended on the substrate species and in-plane direction. The substrate dependence of ionic conduction of amorphous LSO thin film may originate from the structural modulation of the thin film at the vicinity of the hetero-interface.     

电介质材料辐射感应电导率的模型研究

在传统的Rose-Fowler-Vaisberg(RFV)模型基础上引入辐射激发项，解释了辐射感应电导率与辐射剂量率的指数关系及范围.利用改进后的模型分析了不同辐射条件下材料感应电导率的变化情况，其结果表明，辐射剂量率主要影响感应电导率的大小，对感应电导率的整体变化趋势无显著影响，决定感应电导率长时间衰减的是材料载流子复合率.