DC conductivity for NixMg1–xFe2O4 ferrites

The DC electrical conductivity was studied as a function of both composition and temperature for the ferrite system Ni_xMg_1–xFe₂O₄ prepared by the usual ceramic technique. The experimental results proved that, the DC electrical conductivity increases as the temperature increases and as the nickel ion content and porosity decrease. The Curie temperature and the activation energies for electrical conduction increase as the nickel ion content increases.     

Dielectric and ultrasonic investigation of phase transition in cuinp2s6 crystals

Investigation results of dielectric and ultrasonic properties of layered CuInP₂S₆ crystals are presented. At low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 7357.4?K (0.635?eV). The high-frequency part of the spectra is determined by relaxational soft mode. The critical slowing down and Debye-type dispersion show the order–disorder type of the phase transition. The temperature dependence of the relaxational soft mode and dielectric contribution show a quasi-one-dimensional behaviour. Ultrasonic velocity exhibits critical slowing down which is accompanied by attenuation peaks in the phase transition region. Layered CuInP₂S₆ crystals have extremely large elastic nonlinearity in the direction perpendicular to layers. The nonlinear elastic parameters substantially increases at the PT temperature.     

Thermal and electrical studies on composite gel electrolyte system: PEG–PVA–(NH4CH2CO2)2

The present article reports the synthesis and characterisation of a highly conducting composite polymer gel electrolyte, namely polyethylene glycol–polyvinyl alcohol (PVA)–ammonium succinate system. Formation of an amorphous composite gel electrolyte has been evidenced in differential scanning calorimetry experiments. Thermogravimetric analysis of the composite gel electrolyte has shown better thermal stability of films containing 25 wt% PVA. Composite gel system containing 10 wt% PVA exhibits optimal ionic conductivity (4.0 × 10^?4 s cm^?1) and its variation with temperature follows Vogel, Tamman and Fulcher relationship. The magnitude of variation in ionic conductivity (with temperature) of these composite electrolytes and its Williams, Landel and Ferry fit reveals liquid-like charge transport. Composite electrolyte with 25 wt% PVA appears to be a suitable candidate for device applications on the basis of experimental findings.     

Phase transition studies in polymesomorphic compounds(v): Density studies in N-(p-n-Octyloxy benzylidene)-p-n-butyl aniline

The density, ρ, of N-(p-n-octyloxy benzylidene) p-n-butyl aniline (OBBA) is measured as a function of temperature from the isotropic liquid to the smectic-G phase. The compound is trimorphic, exhibiting three smectic phases, smectic-G, crystal smectic-B, and smectic-A phase. The changes in density across the phase transformations and the calculated thermal expansion coefficients confirm the order of the transitions as first order. Particular importance of the smectic-A to crystal smectic-B transformation, which is of first order, is apparent from the density jump across the transition.     

Study of phase transition in a [CdHgI4 : 0.2AgI] mixed conducting composite system doped with KI and K2SO4

New composite superionic systems, [CdHgI₄?:?0.2AgI]?:?0.xKI and [CdHgI₄?:?0.2AgI]?:?0.xK₂SO₄ (x?=?0.2, 0.4, 0.6?mol. wt%), were prepared, using [CdHgI₄?:?0.2AgI] mixed composite system as the host. Electrical conductivity was measured to study the transition behavior at frequencies of 100?Hz, 120?Hz, 1?kHz, and 10?kHz in the temperature range from 150°C to 250°C using a GENRAD 1659 RLC Digibridge. A sharp increase in conductivity was observed during β?→?α phase transition. Upon increasing the dopant-to-host ratio, the conductivity of the superionic systems exhibited Arrhenius (thermally activated)-type behavior. Differential thermal analysis, differential scanning calorimetry, thermogravimetric analysis, and X-ray powder diffraction were performed to confirm the doping effect and transition in the host. The phase transition temperature increased with an increase in the dopant concentration. Activation energies in eV for pre- and post-transition phase behavior are reported.     

Study of electrical conductivity changes and phase transitions in Co3O4 doped ZrO2

The electrical conductivity of ZrO₂ doped with Co₃O₄ has been measured at various temperatures for different molar ratios. The conductivity increases due to the migration of vacancies created by doping. The conductivity is also found to increase with rise in temperature up to 120°C, and after attaining a maximum the conductivity decreases due to a collapse of the lattice framework. A second rise in conductivity around 460°C in all the compositions confirms the phase transition in ZrO₂ from monoclinic to tetragonal symmetry. X-ray powder diffraction and DTA studies were carried out for confirming the doping effects and the transition in ZrO₂.     

Reconstruction of Less Regular Conductivities in the Plane

Abstract

We consider the inverse conductivity problem of how to reconstruct an isotropic electric conductivity distribution in a conductive body from static electric measurements on the boundary of the body. An exact algorithm for the reconstruction of a conductivity in a planer domain from the associated Dirichlet-to-Neumann map is given. We assume that the conductivity has essentially one derivative, and hence we improve earlier reconstruction results. The method relies on a reduction of the conductivity equation to a first order system, to which the ?¯-method of inverse scattering theory can be applied.     

数字化实验在化学核心素养“宏观辨识与微观探析”维度的教学应用——以弱电解质的教学为例

依托人教版《化学反应原理（选修4）》教材,利用数字化实验测定无限稀释冰醋酸过程中的电导率和pH的变化,通过宏观现象观察和图像辨识,从微观上深入解析弱电解质的电离特征,突破越稀越电离的认识边界。在激发学生学习兴趣和学习动力的同时,从“宏观辨识与微观探析”维度帮助学生形成整合的弱电解质结构性知识,探索化学平衡的思维规律。     

Predicting Mole‐Fraction‐Dependent Dissociation for Weak Acids

We demonstrate for formic and acetic acid dissolved in water as examples that the binary quantum cluster equilibrium (bQCE) approach can predict acid strengths over the whole range of acid concentrations. The acid strength increases in a complex rather than a simple way with increasing mole fraction of the acid from 0 to 0.7, reflecting the complex interplay between the dissociated ions or conjugate bases available as compared to the acid and water molecules. Furthermore, our calculated ion concentrations meet the experimental maximum of the conductivity with excellent agreement for acetic acid and satisfactorily for the formic acid/water mixture. As only a limited number of simple quantum‐chemical calculations are required for the prediction, bQCE is clearly a valuable approach to access these quantities also in non‐aqueous solutions. It is a highly valuable asset for predicting ionization processes in highly concentrated solutions, which are relevant for biological and chemical systems, as well as technological processes.     

Adiabatic small polaron-hopping conduction in Ln0.85Ca0.15MnO3 (Ln=Nd, Pr and Sm) perovskites

Polycrystalline bulk ferromagnetic insulating (FMI) Ln_0.85Ca_0.15MnO₃ (Ln=Nd, Pr and Sm) samples are prepared by standard solid-state reaction route and characterized. Powder X-ray diffraction (XRD) data of the manganites show single-phase character. Existing theoretical models predict that the high temperature (T>θ_D/2, θ_D being the Debye temperature) dc conductivity (σ_dc) of these samples is due to adiabatic small polaron-hopping conduction. Greaves’ and Mott's variable range hopping (VRH) conduction mechanisms are not suitable to explain the σ_dc data at low temperature (T<θ_D/2).