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Papers by Irina Kondakova
Solid State Communications, 1995
The calculation of the electric dipoles critical concentration in the disordered ferroelectics wi... more The calculation of the electric dipoles critical concentration in the disordered ferroelectics with the random site elastic dipoles is carried out. The crystals with electrostriction and piezoelectricity in paraelectric phase containing the elastic dipoles with an arbitrary ratio of their dilatation and quadrupole parts are considered. Two cases of the quadrupole axis orientation, namely parallel and transverse to spontaneous polarization direction have been taken into account. It was found that the critical concentration dependence on elastic dipoles concentration is the nonlinear one in the crystals with electrostriction while it is linear in the crystals with piezoelectricity in paraelectric phase. The numerical estimations for KTa03 have shown that the several percents of the elastic dipoles can destroy the ferroelectric phase transition induced by electric dipoles. The distribution function of the random electric fields induced both by the electric and elastic dipoles, which are independent defects in lattice, is calculated for all the aforementioned cases.
Physics of the Solid State, 1998
A theory is developed for the magnetic resonance line shape in disordered ferroelectric crystals.... more A theory is developed for the magnetic resonance line shape in disordered ferroelectric crystals. In a study of the random fields responsible for inhomogeneous line broadening, nonlinear and spatial correlation effects are taken into account. It is shown that homogeneous broadening depends on the temperature and on the magnitude and orientation of the external magnetic field, as well as on the nonlinearity parameters of the ferroelectric material. The resonance line shape is calculated as the envelope of homogeneously broadened Lorentzian spin packets. Analytic expressions for I2(ω) and I3(ω) are introduced to account for nonlinearity and correlation effects of second and third order, respectively. Calculations are done for centrally symmetric crystals, as well as for those without a center of symmetry. It is shown that homogeneous broadening is important near the line peak, while the wings are determined mainly by inhomogeneous broadening. Manifestations of the predicted effects in the spectrum lines of disordered ferroelectric crystals are discussed.
Physical Review B, 2005
ABSTRACT
physica status solidi (b), 1992
The energy of indirect interaction of off‐center ions via conduction electrons is derived. The ca... more The energy of indirect interaction of off‐center ions via conduction electrons is derived. The calculations are carried out for ions described by double‐well potentials with the axis along a cubic axis of the lattice. Tunnel motion of ions is taken into account. It was shown that the obtained electric dipole‐dipole interaction Vdd depends on the values of the ion electric dipole moment, electron wave vector on the Fermi surface, and is an alternating sign function of the distance between the dipoles. The form of this function for the main part of Vdd looks like the well‐known Ruderman‐Kittel interaction of magnetic dipoles. Estimations show that the value of interaction is comparable with the conventional electric dipole‐dipole interaction.
Physical Review B, 2005
The influence of lattice disorder produced by Mn and Fe substitution on the dielectric properties... more The influence of lattice disorder produced by Mn and Fe substitution on the dielectric properties of the incipient ferroelectric KTaO 3 were investigated. Both substituents produce dipolar centers that exhibit relaxational behavior in the audio frequency range. At a concentration of 0.01 at. %, i.e., in the very dilute limits, the Mn center is reflected in a dielectric loss ͑ʦЉ or tan ␦͒ peak, but not to a measurable degree in the real part ͑ʦЈ͒ of the dielectric function, but a concentration of 0.3 at. % Mn produces measurable anomalies in both ʦЈ͑T͒ and the dielectric loss. In the case of Fe, a concentration of 0.3 at. % produces anomalies in the dielectric loss, but not in ʦЈ͑T͒. Hydrostatic pressure has a considerable influence on the static and dynamic properties of these materials and provides insights into the physics. The results are discussed in terms of microscopic models for these dipolar centers, and it is shown that all the properties can be understood in terms of the temperature and pressure dependences of the correlation length for dipolar interactions in the highly polarizable KTaO 3 host lattice-properties unique to soft ferroelectric mode hosts. A model theory was used to describe the influence of random dipolar fields on the reorientation dynamics. The calculations are found to be in good agreement with the experimental data on the 0.3 % Mn where there are weak dipolar correlations.
Physical Review B, 2009
ABSTRACT We have performed density functional calculations for 40- and 90-atom supercells of SrTi... more ABSTRACT We have performed density functional calculations for 40- and 90-atom supercells of SrTiO3 doped by manganese. We use the all-electron, full-potential local-orbital scheme. We show that Mn ion substituting for Sr occupies the off-central position. The ions of the host lattice also change their equilibrium positions when the material is doped, and the ground-state structure becomes polar. The calculated spontaneous magnetic moment of Sr1−xMnxTiO3 is 5 μB/Mn ion, in contrast to SrTi1−xMnxO3 which exhibits the moment of 3 μB/Mn. The calculation results are in accordance with the data of recent ESR and dielectric susceptibility measurements in SrTiO3:Mn ceramics and support the interpretation of observed dielectric anomalies as impurity-induced transition to a polar phase caused by Mn substituting for Sr.
Physical Review B, 2007
ron spin resonance, lattice position and dynamic properties of Mn 2+ ions were studied was tric A... more ron spin resonance, lattice position and dynamic properties of Mn 2+ ions were studied was tric ACS numbers: 61.72.-y, 76.30.Fe, 77.84.Dy Using elect in 0.5 and 2 % manganese doped SrTiO 3 ceramics prepared by conventional mixed oxide method. The measurements showed that Mn 2+ ions substitute preferably up to 97 % for Sr if the ceramics is prepared with a deficit of Sr ions. Motional narrowing of the Mn 2+ ESR spectrum observed when temperature increases from 120 K to 240-250 K that was explained as a manifestation of off-center position of this ion at the Sr site. From the analysis of the ESR spectra the activation energy E a = 86 mV and frequency factor 1/τ 0 ≈ (2-10)⋅10-14 1/s for jumping of the impurity between symmetrical off-center positions were determined. Both values are in agreement with those derived previously from dielectric relaxation. This proves the origin of dielec anomalies in SrTiO 3 :Mn as those produced by the reorientation dynamics of Mn 2+ dipoles.
Physics of the Solid State, 2004
The dynamic dielectric response and the nonlinear dielectric susceptibility of K 1-x Li x TaO 3 (... more The dynamic dielectric response and the nonlinear dielectric susceptibility of K 1-x Li x TaO 3 (x = 0.010, 0.016, 0.030) compounds are measured in a dc electric field in the temperature range 4 ≤ T ≤ 150 K. It is found that the permittivity ε ' of K 1-x Li x TaO 3 samples with two lower concentrations of lithium impurities decreases in an electric field E. For samples with a lithium concentration x = 0.030, the permittivity ε ' decreases in electric fields E > 1 kV/cm and increases in fields E < 0.5 kV/cm. The observed dependences of the maximum of the permittivity on the temperature and the frequency of the measuring field obey the Arrhenius law for samples with lower concentrations of lithium impurities (x = 0.010, 0.016) and the Vogel-Fulcher law for samples with a higher lithium concentration (x = 0.030). The results of the theoretical treatment performed in the framework of the random-field theory are consistent with the experimental data. It is established that the Arrhenius law is valid for dipole glass phases, whereas the Vogel-Fulcher law holds true for a mixed ferroelectric-glass phase in which the short-range and long-range polar orders coexist. The inference is made that the results of measurements of the dielectric response can be used to identify a mixed ferroelectric-glass phase in any disordered ferroelectric material.
Journal of Magnetism and Magnetic Materials
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Eprint Arxiv Cond Mat 0003196, Mar 1, 2000
Theory of the first order Raman scattering (FOR) line shape allowing for nonlinear and correlatio... more Theory of the first order Raman scattering (FOR) line shape allowing for nonlinear and correlation effects contribution to inhomogeneous broadening as well as dynamic mechanisms of homogeneous broadening is developed. It is shown that in general case FOR line contains two maxima, shape of low frequency one being defined by homogeneous broadening. Our theory explains the peculiarity of observed FOR scattering of T O 2 hard phonon in KT L and KT N at different temperatures and concentrations of Li and N b ions.
Physics of the Solid State, 2001
A theory of the shape of the first-order Raman scattering (FORS) line is developed in which nonli... more A theory of the shape of the first-order Raman scattering (FORS) line is developed in which nonlinear and correlation effects in inhomogeneous broadening and the dynamic mechanism of homogeneous broadening are taken into account. It is shown that the FORS band generally has two peaks and that the shape of the low-frequency peak is determined by homogeneous broadening. Our theory provides an explanation for the features of the observed FORS band of the hard TO2 mode in KLT and KTN with various concentrations of Li and Nb ions.
physica status solidi (c), 2007
BaTiO 3 nanopowders with different particle sizes have been studied by Electron Paramagnetic Reso... more BaTiO 3 nanopowders with different particle sizes have been studied by Electron Paramagnetic Resonance method over a temperature range covering the ferroelectric-paraelectric transition. Iron and manganese impurities were used as probes for these experiments. The evolution of the spectra over the transition was observed through 1) the change in symmetry of Fe 3+ from tetragonal to cubic and 2) the appearance beyond T C of Mn 2+ characteristic lines. The results were analyzed according to a theoretical model proposed by one of the authors to extract the distribution of the particles size from the electron paramagnetic resonance spectra. Both the mean particle radius R 0 and the dispersion σ showed a very good agreement with the data obtained from direct measurement of the size distribution. This evidences both the critical influence of the nanoparticles sizes distribution on the EPR spectra's main features and on the temperature dependence of the polarization. In the framework of the theoretical model proposed by one of the authors the distribution of the particles size was extracted from the electron paramagnetic resonance spectra.
Ferroelectrics, 1996
Abstract The distribution function of random electric fields, which allows for the correlation be... more Abstract The distribution function of random electric fields, which allows for the correlation between the sources of electric and elastic fields has been calculated for the first time from the main characteristics of the functions Em and I(E = Em ), the most probable electric field and its maximal intensity, respectively. This made it possible to calculate several parameters of the ferroelectric phase induced by electric dipoles in disordered ferroelectrics. It was shown that the transition temperature Tcmf in the mean field approximation, the piezoelectric tensor components which appear at T < Tcmf , as well as the critical concentration of electric dipoles, decrease with increasing concentration of the elastic dipoles.
Ferroelectrics, 2000
Theory of dielectric spectroscopy spectra developed allowing for homogeneous and inhomogeneous br... more Theory of dielectric spectroscopy spectra developed allowing for homogeneous and inhomogeneous broadening mechanisms contributions. We calculated for the first time dielectric absorption line form for an oscillator with memory and Debye type relaxators with distribution respectively of resonant frequency and relaxation time due to random electric field distribution. The conditions of hole burning observation are discussed. It was shown that the investigation of the inhomogeneously broadened line shape and width, hole burning can give valuable information about the distribution of random field and relaxation time. The latter seems to be extremely important for the disordered systems like supercooled liquids and relaxator ferroelectrics.
Ferroelectrics, 2004
The measurements of dynamic dielectric response and dc-electric field nonlinear susceptibility in... more The measurements of dynamic dielectric response and dc-electric field nonlinear susceptibility in K1−x Li x TaO3 for x = 0.01; 0.016 and 0.03 at 4 ≤ T ≤ 150 K has been performed. It was founded that the field decrease the susceptibility ϵ′ for the two smaller x. For x = 0.03 both the decrease (E > 1 kV/cm) and increase (E < 0.5 kV/cm) of ϵ′ value was revealed. The observed dependence of the position of ϵ′ maxima on temperature and frequency was described by Arrhenius and Vogel–Fulcher law respectively for x = 0.01, 0.016 and x = 0.03. The theoretical description was performed in random field theory framework. The calculations fitted pretty good the experimental data. It was shown that the Arrhenius law is related to the behavior of dipole glass state while Vogel–Fulcher law is the characteristic feature of mixed ferro-glass phase with coexistence of short- and long-range polar order. Therefore the measurements of dielectric response in any disordered ferroelectrics, including relaxors, can be used for identification of ferro-glass phase.
Solid State Communications, 1995
The calculation of the electric dipoles critical concentration in the disordered ferroelectics wi... more The calculation of the electric dipoles critical concentration in the disordered ferroelectics with the random site elastic dipoles is carried out. The crystals with electrostriction and piezoelectricity in paraelectric phase containing the elastic dipoles with an arbitrary ratio of their dilatation and quadrupole parts are considered. Two cases of the quadrupole axis orientation, namely parallel and transverse to spontaneous polarization direction have been taken into account. It was found that the critical concentration dependence on elastic dipoles concentration is the nonlinear one in the crystals with electrostriction while it is linear in the crystals with piezoelectricity in paraelectric phase. The numerical estimations for KTa03 have shown that the several percents of the elastic dipoles can destroy the ferroelectric phase transition induced by electric dipoles. The distribution function of the random electric fields induced both by the electric and elastic dipoles, which are independent defects in lattice, is calculated for all the aforementioned cases.
Physics of the Solid State, 1998
A theory is developed for the magnetic resonance line shape in disordered ferroelectric crystals.... more A theory is developed for the magnetic resonance line shape in disordered ferroelectric crystals. In a study of the random fields responsible for inhomogeneous line broadening, nonlinear and spatial correlation effects are taken into account. It is shown that homogeneous broadening depends on the temperature and on the magnitude and orientation of the external magnetic field, as well as on the nonlinearity parameters of the ferroelectric material. The resonance line shape is calculated as the envelope of homogeneously broadened Lorentzian spin packets. Analytic expressions for I2(ω) and I3(ω) are introduced to account for nonlinearity and correlation effects of second and third order, respectively. Calculations are done for centrally symmetric crystals, as well as for those without a center of symmetry. It is shown that homogeneous broadening is important near the line peak, while the wings are determined mainly by inhomogeneous broadening. Manifestations of the predicted effects in the spectrum lines of disordered ferroelectric crystals are discussed.
Physical Review B, 2005
ABSTRACT
physica status solidi (b), 1992
The energy of indirect interaction of off‐center ions via conduction electrons is derived. The ca... more The energy of indirect interaction of off‐center ions via conduction electrons is derived. The calculations are carried out for ions described by double‐well potentials with the axis along a cubic axis of the lattice. Tunnel motion of ions is taken into account. It was shown that the obtained electric dipole‐dipole interaction Vdd depends on the values of the ion electric dipole moment, electron wave vector on the Fermi surface, and is an alternating sign function of the distance between the dipoles. The form of this function for the main part of Vdd looks like the well‐known Ruderman‐Kittel interaction of magnetic dipoles. Estimations show that the value of interaction is comparable with the conventional electric dipole‐dipole interaction.
Physical Review B, 2005
The influence of lattice disorder produced by Mn and Fe substitution on the dielectric properties... more The influence of lattice disorder produced by Mn and Fe substitution on the dielectric properties of the incipient ferroelectric KTaO 3 were investigated. Both substituents produce dipolar centers that exhibit relaxational behavior in the audio frequency range. At a concentration of 0.01 at. %, i.e., in the very dilute limits, the Mn center is reflected in a dielectric loss ͑ʦЉ or tan ␦͒ peak, but not to a measurable degree in the real part ͑ʦЈ͒ of the dielectric function, but a concentration of 0.3 at. % Mn produces measurable anomalies in both ʦЈ͑T͒ and the dielectric loss. In the case of Fe, a concentration of 0.3 at. % produces anomalies in the dielectric loss, but not in ʦЈ͑T͒. Hydrostatic pressure has a considerable influence on the static and dynamic properties of these materials and provides insights into the physics. The results are discussed in terms of microscopic models for these dipolar centers, and it is shown that all the properties can be understood in terms of the temperature and pressure dependences of the correlation length for dipolar interactions in the highly polarizable KTaO 3 host lattice-properties unique to soft ferroelectric mode hosts. A model theory was used to describe the influence of random dipolar fields on the reorientation dynamics. The calculations are found to be in good agreement with the experimental data on the 0.3 % Mn where there are weak dipolar correlations.
Physical Review B, 2009
ABSTRACT We have performed density functional calculations for 40- and 90-atom supercells of SrTi... more ABSTRACT We have performed density functional calculations for 40- and 90-atom supercells of SrTiO3 doped by manganese. We use the all-electron, full-potential local-orbital scheme. We show that Mn ion substituting for Sr occupies the off-central position. The ions of the host lattice also change their equilibrium positions when the material is doped, and the ground-state structure becomes polar. The calculated spontaneous magnetic moment of Sr1−xMnxTiO3 is 5 μB/Mn ion, in contrast to SrTi1−xMnxO3 which exhibits the moment of 3 μB/Mn. The calculation results are in accordance with the data of recent ESR and dielectric susceptibility measurements in SrTiO3:Mn ceramics and support the interpretation of observed dielectric anomalies as impurity-induced transition to a polar phase caused by Mn substituting for Sr.
Physical Review B, 2007
ron spin resonance, lattice position and dynamic properties of Mn 2+ ions were studied was tric A... more ron spin resonance, lattice position and dynamic properties of Mn 2+ ions were studied was tric ACS numbers: 61.72.-y, 76.30.Fe, 77.84.Dy Using elect in 0.5 and 2 % manganese doped SrTiO 3 ceramics prepared by conventional mixed oxide method. The measurements showed that Mn 2+ ions substitute preferably up to 97 % for Sr if the ceramics is prepared with a deficit of Sr ions. Motional narrowing of the Mn 2+ ESR spectrum observed when temperature increases from 120 K to 240-250 K that was explained as a manifestation of off-center position of this ion at the Sr site. From the analysis of the ESR spectra the activation energy E a = 86 mV and frequency factor 1/τ 0 ≈ (2-10)⋅10-14 1/s for jumping of the impurity between symmetrical off-center positions were determined. Both values are in agreement with those derived previously from dielectric relaxation. This proves the origin of dielec anomalies in SrTiO 3 :Mn as those produced by the reorientation dynamics of Mn 2+ dipoles.
Physics of the Solid State, 2004
The dynamic dielectric response and the nonlinear dielectric susceptibility of K 1-x Li x TaO 3 (... more The dynamic dielectric response and the nonlinear dielectric susceptibility of K 1-x Li x TaO 3 (x = 0.010, 0.016, 0.030) compounds are measured in a dc electric field in the temperature range 4 ≤ T ≤ 150 K. It is found that the permittivity ε ' of K 1-x Li x TaO 3 samples with two lower concentrations of lithium impurities decreases in an electric field E. For samples with a lithium concentration x = 0.030, the permittivity ε ' decreases in electric fields E > 1 kV/cm and increases in fields E < 0.5 kV/cm. The observed dependences of the maximum of the permittivity on the temperature and the frequency of the measuring field obey the Arrhenius law for samples with lower concentrations of lithium impurities (x = 0.010, 0.016) and the Vogel-Fulcher law for samples with a higher lithium concentration (x = 0.030). The results of the theoretical treatment performed in the framework of the random-field theory are consistent with the experimental data. It is established that the Arrhenius law is valid for dipole glass phases, whereas the Vogel-Fulcher law holds true for a mixed ferroelectric-glass phase in which the short-range and long-range polar orders coexist. The inference is made that the results of measurements of the dielectric response can be used to identify a mixed ferroelectric-glass phase in any disordered ferroelectric material.
Journal of Magnetism and Magnetic Materials
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Eprint Arxiv Cond Mat 0003196, Mar 1, 2000
Theory of the first order Raman scattering (FOR) line shape allowing for nonlinear and correlatio... more Theory of the first order Raman scattering (FOR) line shape allowing for nonlinear and correlation effects contribution to inhomogeneous broadening as well as dynamic mechanisms of homogeneous broadening is developed. It is shown that in general case FOR line contains two maxima, shape of low frequency one being defined by homogeneous broadening. Our theory explains the peculiarity of observed FOR scattering of T O 2 hard phonon in KT L and KT N at different temperatures and concentrations of Li and N b ions.
Physics of the Solid State, 2001
A theory of the shape of the first-order Raman scattering (FORS) line is developed in which nonli... more A theory of the shape of the first-order Raman scattering (FORS) line is developed in which nonlinear and correlation effects in inhomogeneous broadening and the dynamic mechanism of homogeneous broadening are taken into account. It is shown that the FORS band generally has two peaks and that the shape of the low-frequency peak is determined by homogeneous broadening. Our theory provides an explanation for the features of the observed FORS band of the hard TO2 mode in KLT and KTN with various concentrations of Li and Nb ions.
physica status solidi (c), 2007
BaTiO 3 nanopowders with different particle sizes have been studied by Electron Paramagnetic Reso... more BaTiO 3 nanopowders with different particle sizes have been studied by Electron Paramagnetic Resonance method over a temperature range covering the ferroelectric-paraelectric transition. Iron and manganese impurities were used as probes for these experiments. The evolution of the spectra over the transition was observed through 1) the change in symmetry of Fe 3+ from tetragonal to cubic and 2) the appearance beyond T C of Mn 2+ characteristic lines. The results were analyzed according to a theoretical model proposed by one of the authors to extract the distribution of the particles size from the electron paramagnetic resonance spectra. Both the mean particle radius R 0 and the dispersion σ showed a very good agreement with the data obtained from direct measurement of the size distribution. This evidences both the critical influence of the nanoparticles sizes distribution on the EPR spectra's main features and on the temperature dependence of the polarization. In the framework of the theoretical model proposed by one of the authors the distribution of the particles size was extracted from the electron paramagnetic resonance spectra.
Ferroelectrics, 1996
Abstract The distribution function of random electric fields, which allows for the correlation be... more Abstract The distribution function of random electric fields, which allows for the correlation between the sources of electric and elastic fields has been calculated for the first time from the main characteristics of the functions Em and I(E = Em ), the most probable electric field and its maximal intensity, respectively. This made it possible to calculate several parameters of the ferroelectric phase induced by electric dipoles in disordered ferroelectrics. It was shown that the transition temperature Tcmf in the mean field approximation, the piezoelectric tensor components which appear at T < Tcmf , as well as the critical concentration of electric dipoles, decrease with increasing concentration of the elastic dipoles.
Ferroelectrics, 2000
Theory of dielectric spectroscopy spectra developed allowing for homogeneous and inhomogeneous br... more Theory of dielectric spectroscopy spectra developed allowing for homogeneous and inhomogeneous broadening mechanisms contributions. We calculated for the first time dielectric absorption line form for an oscillator with memory and Debye type relaxators with distribution respectively of resonant frequency and relaxation time due to random electric field distribution. The conditions of hole burning observation are discussed. It was shown that the investigation of the inhomogeneously broadened line shape and width, hole burning can give valuable information about the distribution of random field and relaxation time. The latter seems to be extremely important for the disordered systems like supercooled liquids and relaxator ferroelectrics.
Ferroelectrics, 2004
The measurements of dynamic dielectric response and dc-electric field nonlinear susceptibility in... more The measurements of dynamic dielectric response and dc-electric field nonlinear susceptibility in K1−x Li x TaO3 for x = 0.01; 0.016 and 0.03 at 4 ≤ T ≤ 150 K has been performed. It was founded that the field decrease the susceptibility ϵ′ for the two smaller x. For x = 0.03 both the decrease (E > 1 kV/cm) and increase (E < 0.5 kV/cm) of ϵ′ value was revealed. The observed dependence of the position of ϵ′ maxima on temperature and frequency was described by Arrhenius and Vogel–Fulcher law respectively for x = 0.01, 0.016 and x = 0.03. The theoretical description was performed in random field theory framework. The calculations fitted pretty good the experimental data. It was shown that the Arrhenius law is related to the behavior of dipole glass state while Vogel–Fulcher law is the characteristic feature of mixed ferro-glass phase with coexistence of short- and long-range polar order. Therefore the measurements of dielectric response in any disordered ferroelectrics, including relaxors, can be used for identification of ferro-glass phase.