Object of the study: relaxation processes after external influences, which lead to reversible and
irreversible changes in the properties of piezoelectric ceramic elements based on solid solutions of
Pb(Zr,Ti)O3 ; mechanisms that lead to nonlinear features of relaxation processes. Objective: to solve
an urgent scientific task, which is to establish the physical nature and patterns of relaxation
processes that occur after the cessation of external factors in solid solutions of Pb(Zr,Ti)O3 and build
a physical model of these processes. Methods: measurement of dielectric hysteresis loops P(E) in the
quasi-static mode (f = 2∙10 -2 Hz) according to the Sawyer-Tower scheme; measurement of the
temperature dependence of the dielectric constant ε(T); measurement of the temperature dependence
of the polarization P(T); X-ray structural studies performed using an X-ray diffractometer DRON-3;
microstructural studies performed by scanning electron microscopy (Selmi REM-106I);
measurement of dielectric properties (capacitance C, tangent of dielectric loss angle tgδ) at a
frequency of 1 kHz at an amplitude of the measuring field of 4.3 V by the bridge method (E7-8);
measurement of piezoresonant properties (fr , fa , fr.3 ) by the passive quadrupole method; measurement
of the piezoelectric module d33 by the static method; measurement of relaxation properties during
aging after cessation of external influence ε(t), fr(t). Theoretical and practical results, scientific
novelty: 1. Found the further development of the idea that relaxation in polycrystalline ferroelectric
materials occurs by the logarithmic law. This is experimentally shown by the example of relaxation
of the dielectric constant of ferroceramics Pb(Zr,Ti)O3 after the action of temperature, electric field,
mechanical stress. Such behavior is possible in the presence of a spectrum of relaxation times in
polycrystalline solid solutions of Pb(Zr,Ti)O3 , which contain structural defects with different
activation energies. 2. It was found for the first time that after cessation of partial repolarization by a
constant electric field and depolarization by heating, the relaxation rate of dielectric constant has a
maximum value at field and temperature values below the coercive field and Curie point
temperature, respectively (Ecr < Eс , Tcr < TC ). The field E cr and temperature T cr are the limits for
reversible processes. In the range of Eс – Ecr fields and TC – Tcr temperatures, the sample undergoes
irreversible repolarization and depolarization; in the relaxation process, the dielectric constant does
not return to its original value, and the domain structure changes. 3. It is shown for the first time that
the intervals Eс – Ecr and TC – Tcr increase during the transition from the rhombohedral region of the
phase diagram of solid solutions Pb(Zr,Ti)O3 to tetragonal, which is explained by higher values of
the homogeneous deformation parameter of tetragonal structure in comparison with rom. 4. It was
first established that the nonlinear dependence of the relaxation characteristics of piezoelectric
ceramics based on Pb(Zr,Ti)O3 on the amplitude of external factors is determined by the
rearrangement of the domain structure. 5. A model of the mechanism of long-term relaxation is
developed, which is based on the change of the charge state of the crystal lattice defects (oxygen
vacancies VO ), which occurs at the following stages: − reduction of residual polarization and
uncompensated charge on the surface during external actions; charged oxygen vacancies) by the
mechanism VO + e → F+ , VO + 2e → F0 ; − violation of the electric balance, which was before
excitation, and the generation of an electric field, which is directed against polarization, by a new
distribution of charges; − inverse long-term transition after termination of external actions of excited
states according to the scheme F+ → VO + e , F0 → VO + 2e and the long-term relaxation of the
piezoelectric sample to the ground state caused by it. Practical significance: the results obtained
during the dissertation work expand the existing ideas about the physical processes occurring in
ferroelectric piezoceramic materials after the cessation of external factors. The logarithmic law of
relaxation, which satisfactorily describes the experimental data, makes it possible to predict the
behavior of the properties of the samples during aging. Determining the limiting amplitudes that
lead to reversible or irreversible changes in properties makes it possible to increase the service life
of piezoceramic elements that are part of electronic equipment. Scope of application: the mechanism
of long-term relaxation of the aftereffect offered in the work gives the chance to carry out
purposeful search of new highly effective piezoelectric ceramic materials.
