Current limiting and negative differential resistance in indium oxide based ceramics

Indium oxide based ceramics with bismuth oxide addition were sintered in air in the temperature range 800-1300 ºC. Current-voltage characteristics of In2O3-Bi2O3 ceramics sintered at different temperatures are weakly nonlinear. After an additional heat treatment in air at about 200 ºC samples sintered at a temperature within the narrow range of about 1050-1100 ºC exhibit a current-limiting effect accompanied by low-frequency current oscillations. It is shown that the observed electrical properties are controlled by the grain-boundary barriers and the heat treatment in air at 200 ºC leads to the decrease in the barrier height. Electrical measurements, scanning electron microscopy and X-ray photoelectron spectroscopy results suggest that the current-limiting effect observed in In2O3-Bi2O3 may be explained in terms of a modified barrier model; the observed current-limiting effect is the result of an increase of barrier height with increasing electric field, due to additional oxygen absorption. It is found that In2O3-Bi2O3-Co3O4-Cr2O3 ceramic exhibits current-voltage characteristics with negative differential resistance due to Joule micro heating.This study was performed in part in the frames of the project SEP-2003-C02-42821, CONACYT, México. Funding from the Royal Society, United Kingdom (2007R1/R26999) is gratefully acknowledged

Effect of sintering temperature and heat treatment on electrical properties of indium oxide based ceramics

Indium oxide based ceramics with bismuth oxide addition were sintered in air in the temperature range 800-1300 ºC. Current-voltage characteristics of In2O3-Bi2O3 ceramics sintered at different temperatures are weakly nonlinear. After an additional heat treatment in air at about 200 ºC samples sintered at a temperature within the narrow range of about 1050-1100 ºC exhibit a current-limiting effect accompanied by low-frequency current oscillations. It is shown that the observed electrical properties are controlled by the grain-boundary barriers and the heat treatment in air at 200 ºC leads to the decrease in the barrier height. Electrical measurements, scanning electron microscopy and X-ray photoelectron spectroscopy results suggest that the current-limiting effect observed in In2O3-Bi2O3 can be explained in terms of the modified barrier model proposed earlier for the explanation of similar effect in In2O3-SrO ceramics

Electronic properties of SnO2-based ceramics with double function of varistor and humidity sensor

This is the post-print version of the article. The official published version can be obtained from the link below - Copyright @ 2010 AD-Tech.Tin dioxide based varistor ceramics SnO2-Co3O4-Nb2O5-Cr2O3-xCuO (x=0; 0.05; 0.1 and 0.5) were made and their electrical properties were studied. The highest nonlinearity coefficient and electric field (at current density 10-3 A cm-2) were obtained for 0.1 mol.% CuO addition. It was observed that low-field electrical conductivity is increased with relative humidity, therefore, materials obtained exhibit double function of varistor and humidity sensor. The highest humidity sensitivity coefficient is found for SnO2-Co3O4-Nb2O5-Cr2O3 ceramics (without CuO). Observed varistor and humidity-sensitive properties are explained in the frames of grain-boundary double Schottky barrier concept as a decrease of the barrier height with electric field or relative humidity. Using suggested simple theory and data obtained on isothermal capacitance relaxation, the energy of the grain-boundary monoenergetic trapping states were estimated. These values are less than found for activation energy of electrical conduction (as a measure of the barrier height). These observations confirm the barrier concept.This work is funded by the Royal Society, United Kingdom (2007R1/R26999)

Non-ohmic conduction in tin dioxide based ceramics with copper addition

The current-voltage characteristics and temperature dependences of electrical conductivity in SnO₂-Co₃O₄-Nb₂O₅-Cr₂O₃-CuO semiconductor ceramics are studied, and possible mechanism of non-ohmic conduction in these materials is discussed. Due to addition of CuO up to 0.5 mol.%, the nonlinearity coefficient is increased up to 75, and the electric field is decreased down to 3900 V∙cm¹ (at 1 mA∙cm⁻²). It makes CuO addition useful for the preparation of SnO₂-based varistors. It is concluded that the electrical conduction is controlled by grain-boundary barriers. The activation energy of electrical conduction (the barrier height φ) is decreased with an increase in the electric field E. The higher slope of the dependence at high fields can be related to a participation of minority carriers (holes). The addition of more than 0.5 mol.% CuO leads to degradation of the varistor effect due to percolation via quite conductive CuO-based intergranular phase

Estimation of the nonlinear dependence of the indications of a fiber Bragg grating on temperature and strain from experimental data

The readings of the Bragg grating are determined based on the optical radiation reflected from it. A quantitative characteristic of this radiation is the wavelength at which the maximum power of the optical signal is achieved. This characteristic is called the central wavelength of the grating. The central wavelength shift depends on temperature and strain. As a rule, a linear approximation of this dependence is used. However, from the available literature it is known that, the grating wavelength shift demonstrates a strong nonlinear dependence on temperature at 5<T<200K and a weak quadratic dependence close to room temperature. Thus far, the authors have not found studies that consider all terms in the quadratic expansion of the central wavelength of the Bragg grating as a function of temperature and strain at near-room temperatures. Our work is intended to fill this gap. The article describes an experiment in which an optical fiber with Bragg grating was subjected to loading using three different weights. A step-wise temperature change from 5 to 100 0С was realized for each weight. Based on these data, all terms of the quadratic expansion of the desired function are determined. The contribution of each term is estimated

Simulation of Movement of the Device with Passive Vibration Isolation

Modern electronic systems, computer hardware and navigation equipment on board moving objects can be subjected to significant mechanical impulse and vibrational impacts. These impacts can introduce additional errors in readings of devices, and sometimes lead to their mechanical failure. One of the effective ways to solve the problem is to apply the method of passive vibration protection, which makes it possible to reduce vibrations due to the use of damping elements. This paper examines the vibration response of a device mounted on a moving platform. The device is protected against vibration by 4 dampers. The platform is subjected to translational motions in three mutually orthogonal directions. This leads to the appearance of coupled translational and rotational vibrations of the protected unit. The problem is solved within the framework of the general theory of the dynamic of a rigid body. The paper presents the results of numerical experiments, in which the intensity of rotational vibrations of the protected unit is investigated depending on various mechanical characteristics of the system. Admissible variation of these characteristics, at which the angular acceleration of the protected unit remains below a limit value, has been determined

Investigation of the effect of cracks on the vibration processes in reinforced concrete structures

The validity of the mathematical model describing the propagation of vibrations in the reinforced concrete structures (RC structures) was verified by comparing the experimental and numerical data. The proposed model allowed us to perform numerical experiments aimed at comparing vibrorecords obtained for the structure without defects and the structure with typical fracture caused by crack formation. Based on the results of comparison, an informative diagnostic parameter was proposed. This parameter makes it possible to control the nucleation and growth of cracks in a RC structure

Investigation of the effect of cracks on the vibration processes in reinforced concrete structures

The validity of the mathematical model describing the propagation of vibrations in the reinforced concrete structures (RC structures) was verified by comparing the experimental and numerical data. The proposed model allowed us to perform numerical experiments aimed at comparing vibrorecords obtained for the structure without defects and the structure with typical fracture caused by crack formation. Based on the results of comparison, an informative diagnostic parameter was proposed. This parameter makes it possible to control the nucleation and growth of cracks in a RC structure

Control of surface subsidence based on building deformation monitoring data

This paper presents an approach to the estimation of ground surface distortion based on the data from the online deformation monitoring systems mounted on the foundations of the group of buildings located in the area of ground instability. The local monitoring systems provide control of building foundation settlements using the hydrostatic level measurement technique. These data are used to calculate the inclination foundation angles which reflect the distortion of the earth's surface at local points. The hydrostatic level system allows one to perform measurements with the desired space and time sampling and to obtain a quite detailed picture of the changes in the deformation parameters over time. A set of such local monitoring units forms a distributed system that allows monitoring the state of the earth's surface over a large area. Here, we present long-term results obtained using such system located in the city area above mining. The evolution of the inclination angles of the group of overlying buildings is shown. We discuss the validity of this approach, and estimate the accuracy of the measuring method and the factors that influence it. Finally, we assess the possibility of making short-term predictions of deformation processes inside the rock massif

Process of cracking in reinforced concrete beams (simulation and experiment)

The paper presents the results of experimental and theoretical investigations of the mechanisms of crack formation in reinforced concrete beams subjected to quasi-static bending. The boundary-value problem has been formulated in the framework of brittle fracture mechanics and solved using the finite-element method. Numerical simulation of the vibrations of an uncracked beam and a beam with cracks of different size serves to determine the pattern of changes in the spectrum of eigenfrequencies observed during crack evolution. A series of sequential quasi-static 4-point bend tests leading to the formation of cracks in a reinforced concrete beam were performed. At each loading step, the beam was subjected to an impulse load to induce vibrations. Two stages of cracking were detected. During the first stage the nonconservative process of deformation begins to develope, but has not visible signs. The second stage is an active cracking, which is marked by a sharp change in eingenfrequencies. The boundary of a transition from one stage to another is well registered. The vibration behavior was examined for the ordinary concrete beams and the beams strengthened with a carbon-fiber polymer. The obtained results show that the vibrodiagnostic approach is an effective tool for monitoring crack formation and assessing the quality of measures aimed at strengthening concrete structures