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  • Dependence of the stationary current in the ferroelectric ceramics (1-x)Ва0.95Pb0.05TiO3+xCo2O3 on doping with cobalt under the action of radiation in the optical range

    The article presents the results of a study of the photoelectric response of cobalt-containing ferroelectric ceramics (1-x)Ва0.95Pb0.05TiO3+xCo2O3, synthesized at the Institute of Solid State Physics of the University of Latvia using conventional ceramic technology. Ceramics was exposed to optical radiation at room temperature. Before applying light radiation to the cellular electrode of the ceramic sample located in the measuring cell, zero current was recorded for 0.5 minutes in the absence of illumination using a high sensitivity digital electrometer. Then, the photoresponse was recorded during the time until its value remained constant (since the anomalous photovoltaic effect manifests itself in the form of constant currents flowing along the polar directions) and only then the light flux was turned off. A significant effect of the concentration of cobalt oxide on the value of the photovoltaic current is shown, which manifests itself in a decrease in the value of the stationary current with an increase in the content of the impurity of cobalt oxide. It is assumed that a possible reason for the decrease in the stationary current is deep charge traps, which is due to an increase in the cobalt concentration in the ceramic. The influence of the incident radiation wavelength, as well as the aging factor on the photoelectric response for ceramics with the highest concentration of cobalt oxide, is established.

    Keywords: mobile robots, polarization, depolarization, ferroelectrics, polarization current, remanent polarization, dielectric losses, electrical load, domain structure, electrical breakdown, mechanical failure

  • Features of the dependence of the repolarization current in ferroceramics on the mutual orientation of the electric field intensity vector and the remaining polarization

    The results of the analysis of leakage currents as a function of time in samples of polycrystalline ferroelectric ceramics solid solutions of lead titanate-zirconate with sodium and bismuth impurities under the condition of applying a constant electric field are presented. We considered batches of samples that were stored in different conditions, which led to the formation of two batches - standard and defective. The samples of the standard and defective batches differed in values of the dielectric loss tangent by several times, while other electrophysical parameters practically did not differ. To measure the patterns of current fluctuations with time in the sample, a modernized Mertz scheme was used. The electric field was changed stepwise on the sample. Current fluctuations at a constant voltage across the sample were measured during the establishment of a constant leakage current and were considered as a time series, allowing only a statistical description. Changes in the form of the dependence of the leakage current on time are determined with an increase in the electric field strength on samples with different values of the loss tangent. The exponential decline is accompanied by random jumps in the magnitude of the leakage current. It is assumed that at a higher voltage, the state of the domain regions stabilizes, resulting in current leakage under a depolarizing field, since the domain system retains its more rigid configuration.

    Keywords: mobile robots, polarization, depolarization, ferroelectrics, polarization current, remanent polarization, dielectric losses, electrical load, domain structure, electrical breakdown, mechanical failure

  • Simulation of the polarization currents of ferroelectric ceramics, arising from the simultaneous application of an electric field and mechanical stresses

    The operating conditions of polycrystalline dielectrics in external mechanical and electric fields make it relevant to study the properties of such materials and their resistance to extreme loads, which depends on the processes of polarization reversal and the dynamics of the domain structure. Based on the model of motion of domain walls and the rheological model, equations are obtained for the dependence of polarization on the applied mechanical, electrical, or simultaneous electromechanical load. It is shown that the nonlinearity of the current in the ferroelectric ceramic is due to the dependence of the coefficients of the model on the through conduction current and the current associated with the emission of charges from traps. The physical meaning of the coefficients makes it possible to use their well-known dependences on the electric field and external mechanical stresses both in the range of the linear piezoelectric effect and in the region of external loads, when linearity ceases to exist. The obtained coefficients make it possible to pass from polarization (macroscopic parameter) to domain walls (mesoscopic scale). The parameters of the model depend on the change in the domain structure and its interaction with defects; therefore, the current relaxation time in the ferroceramic is described by changing the corresponding times for 180°-domains and non-180°-domains. The model considers two polarization components: elastic and irreversible. Changes in polarization after the external action of the electric field can be explained by the movement of domain and interphase boundaries. When a critical mechanical load is applied, the domain boundaries are detached from the defects and the crack grows abruptly, and as a result, destruction occurs. The relaxation motion of domain walls with constant friction leads to the growth of cracks due to the creation of mechanical stresses. The chosen rheological model and approach, taking into account the mechanisms of motion of domain walls, will make it possible to describe the rate of polarization change using the behavior of defects (dislocations, domain walls). The model will allow from a unified point of view to describe the experimental patterns of the behavior of currents under electromechanical action.

    Keywords: ferroelectric ceramics, computer simulation, rheological model, polarization current, polarization current density, domain wall, 1800-domains, not 1800-domains, mechanical load, electrical load, relaxation time