I. P. Aleksandrova

Russian Academy of Sciences, Moskva, Moscow, Russia

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Publications (68)77.37 Total impact

  • Source
    I. P. Aleksandrova · A. A. Sukhovsky · Yu. N. Ivanov · I. P. Raevsky
    [Show abstract] [Hide abstract] ABSTRACT: The local structure of the ferroelectric-relaxor PbSc1/2Nb1/2O3 in the temperature range from 550 to 220 K has been investigated using 45Sc nuclear magnetic resonance. It has been found that, in the paraelectric phase at temperatures below 550 K, the crystal consists of regions of an ordered elpasolite structure and inclusions of the disordered tetragonal perovskite phase with displacements along directions of the [001] type. The relative weight of the tetragonal structure in the region of the paraelectric phase is approximately equal to 0.28. Below the temperature of the phase transition from the disordered modification to the polar phase, the relative weight of the tetragonal phase decreases with decreasing temperature. The tetragonal structure is replaced by the trigonal polar structure. In a wide temperature range (∼50 K), there exists a heterophase structure that is characteristic of relaxors. Note that the correlation length of displacements in the tetragonal phase should be very small to explain the absence of indications of the existence of this phase in the diffraction data.
    Full-text · Article · Feb 2012 · Physics of the Solid State
  • V. L. Mironov · A. A. Sukhovskii · Yu. I. Lukin · I. P. Aleksandrova
    [Show abstract] [Hide abstract] ABSTRACT: An investigation of moisture dependences of refractive index and spectral width of the nuclear magnetic resonance (NMR) is performed for bentonitic clay specimens at different temperatures. These moisture dependences allowed identifying two types of moisture: bound and free water. The maximum content of water in the bentonitic clay is measured. Keywordsdielectric permittivity–nuclear magnetic resonance–bentonitic clay–bound water
    No preview · Article · Jun 2011 · Russian Physics Journal
  • [Show abstract] [Hide abstract] ABSTRACT: 23 Na NMR spectra have been measured in a very low magnetic field at temperatures between 203 K and 780 K. The orientation dependences of the second-order quadrupole shifts of the central component were studied. The achieved spectral resolution is sufficient to test various models of short –range order in the Na 1/2 Bi 1/2 TiO 3 (NBT) structure using computer simulations of the spectral line shape. The polar monoclinic areas were found to coexist with the tetragonal phase insertions till the lowest investigated temperature 203 K. In the temperature range 203 K – 640 K the NMR spectra also display the presence of areas with very small deviation from the cubic structure (matrix).
    No preview · Article · Sep 2010 · Ferroelectrics
  • Source
    V.L. Mironov · A.A. Suhovskiy · Yu.I. Lukin · I.P. Aleksandrova
    [Show abstract] [Hide abstract] ABSTRACT: The maximum bound water content (MBWC) in moist bentonite clay was detected with the use of two dielectric models, that is, the Generalized Refractive Mixing Dielectric Model and Schmugge dielectric model. These values have appeared to be different. To determine which of these values corresponds to the true MBWC value, there was developed an independent nuclear magnetic resonance (NMR) technique for measuring the MBWC. The three MBWCs, attained with three methods, were compared, showing the NMR technique to provide for the MBWC value closer to that obtained with the use of the GRMDM.
    Full-text · Conference Paper · Jul 2010
  • I.P. Aleksandrova · Y.N. Ivanov · V.S. Bondarev · A.A. Sukhovskii · V.N. Voronov
    [Show abstract] [Hide abstract] ABSTRACT: The heat capacity of NaNb1_xTaxO3 solid solutions was measured in the temperature range 100 to 770 K. The step-like change of phase transition temperature is observed in the T-x phase diagram at concentration x = 0.55. The obtained results are in a good agreement with the data of dielectric studies. The 23Na MAS NMR spectra were obtained at Larmor frequency 79.35 MHz using a Bruker AVANCE 300 spectrometer. The quadru-polar coupling constant, (CQ=e2qQ/h) and asymmetry parameter (n) were determined by computer fitting of the NMR line shape using the DMFit software. The found parameters show that solid solution structure is NaTa03-based at 0.7<X ≤1 and NaNbO3-based at 0≤x≤0.5. The spectra in the intermediate region (0.5<x≤0.7) can be described at a reasonable accuracy when assuming the coexistence of NaTaO3 and NaNbO3 structures.
    No preview · Article · Jan 2010
  • [Show abstract] [Hide abstract] ABSTRACT: The maximum bound water content (MBWC) in moist bentonite clay was detected with the use of two dielectric models, that is, the Generalized Refractive Mixing Dielectric Model and Schmugge dielectric model. These values have appeared to be different. To determine which of these values corresponds to the true MBWC value, there was developed an independent nuclear magnetic resonance (NMR) technique for measuring the MBWC. The three MBWCs, attained with three methods, were compared, showing the NMR technique to provide for the MBWC value closer to that obtained with the use of the GRMDM.
    No preview · Conference Paper · Jan 2010
  • [Show abstract] [Hide abstract] ABSTRACT: The orientation dependences of the second-order quadrupole shifts of the central component in the 23Na NMR spectrum were studied in the temperature range 293–760 K. The profile of the spectral distribution is calculated using various models of the Na1/2Bi1/2TiO3 structure. The calculations agree with the experimental data for the monoclinic structure of a polar cluster with two Na displacement components: a displacement along the [111]p direction and a small displacement statistically or dynamically disordered over six equally probable [100]p -type directions. Tetragonal-phase nuclei and monoclinic clusters with a very small displacement component along the [111]p direction are found to coexist and have close energies over the temperature range 580–610 K. The results obtained provide new information concerning the character of the diffuse phase transition at 610 K.
    No preview · Article · Mar 2008 · Physics of the Solid State
  • Yu. N. Ivanov · I. P. Aleksandrova · A. A. Sukhovsky · A. I. Baranov
    [Show abstract] [Hide abstract] ABSTRACT: A crystal of the Cs5H3(SO4)4 · xH2O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by 2H NMR spectroscopy. The temperature and orientation dependences of the 2H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature T g = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point T g . However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.
    No preview · Article · Jun 2007 · Physics of the Solid State
  • Yu. N. Ivanov · A. A. Sukhovsky · I. P. Aleksandrova · D. Michel
    [Show abstract] [Hide abstract] ABSTRACT: The proton exchange in a potassium hydrogen selenate crystal is investigated in detail. Partial deuteration of the crystal (approximately 80% of the protons are replaced by deuterons) makes it possible to use the method of nuclear magnetic resonance (NMR) on quadrupole nuclei to perform research into proton (deuteron) transport. In addition to conventional Fourier-transform NMR spectroscopy, elementary processes of deuteron chemical exchange are studied by two-dimensional NMR spectroscopy, which provides unique information regarding these processes. Slow exchange between protons of hydrogen bond chains and dimers consisting of two SeO4 groups is revealed. It is established that this process is responsible for the proton conduction in the potassium hydrogen selenate. The NMR data are compared with the results of dielectric measurements carried out at a frequency of 1 kHz.
    No preview · Article · Sep 2006 · Physics of the Solid State
  • I. P. Aleksandrova · Yu. N. Ivanov · A. A. Sukhovskiĭ · S. B. Vakhrushev
    [Show abstract] [Hide abstract] ABSTRACT: The 23Na NMR spectra of a Na1/2Bi1/2TiO3 crystal are studied at frequencies of 79.4 and 15.7 MHz in the temperature range 150–720 K. It is revealed that, at all temperatures, the crystal contains regions with a nearly cubic matrix and polar clusters. The temperature dependence of the local distortion of the Na environment in the clusters is determined. The dynamics of the reorientation of the local cluster polarization in the tetragonal and trigonal NBT phases is analyzed.
    No preview · Article · Jun 2006 · Physics of the Solid State
  • Yu. N. Ivanov · A. A. Sukhovsky · I. P. Aleksandrova · D. Michel
    [Show abstract] [Hide abstract] ABSTRACT: The microscopic mechanism of proton transport in partially deuterated potassium hydrogen selenate (KHSe) and in partially deuterated ammonium hydrogen selenate (AHSe) were studied by means of one-dimensional Fourier transform2H nuclear magnetic resonance (NMR), two-dimensional2H NMR and dielectric measurements over a wide temperature range. In both systems, KHSe and AHSe, the slow chemical exchange processes of deuterons between different hydrogen bridges occur. It was established that the rates of exchange between deuteron sites, which are involved in infinite chains of hydrogen bonds, are approximately the same for both crystals. The rates of exchange between these positions and the deuterons in the dimer groups of KHSe are approximately hundred times more slowly. On the basis of our findings, we discuss the models of the microscopic mechanism of hydrogen transport for both substances.
    No preview · Article · Sep 2005 · Applied Magnetic Resonance
  • Yu. N. Ivanov · AA Sukhovskii · I. P. Aleksandrova · J. Totz · D. Michel
    [Show abstract] [Hide abstract] ABSTRACT: The ion mobility in a crystal of partially deuterated potassium hydroselenate (KHSe) was studied using nuclear spin resonance (NSR) of 1H, 2H, 77Se, and 39K in a wide temperature range. The temperature dependences of the deuterium NSR spectra above 360 K exhibit changes in the line shape characteristic of chemical exchange processes. These exchange processes were studied in detail using two-dimensional 2H NSR spectroscopy. It was ascertained that the exchange between deuterons of hydrogen bonds take place in the entire temperature range under study. However, the measured conductivity was approximately one-hundredfold lower than that estimated from the exchange frequencies. It was assumed that the low conductivity in the temperature range under study is caused by closed dimers of SeO4 groups in the KHSe structure.
    No preview · Article · Oct 2004 · Physics of the Solid State
  • I P Aleksandrova · J Bartolomé · L R Falvello · J M Torres · A A Sukhovskii
    [Show abstract] [Hide abstract] ABSTRACT: The heat capacity, nuclear quadrupole resonance (NQR) and x-ray diffraction of (Cs1−xRbx)2ZnI4 single crystals have been measured, for x = 0, 0.001, 0.005, 0.01, 0.025 and 0.05. The normal to incommensurate (N–Inc) phase transition at TI, the incommensurate to commensurate (Inc–C) lock-in transition at TL and the structural commensurate monoclinic to triclinic transition at TLT, observed in the parent compound (x = 0), takes place for x = 0, 0.001, 0.005 and 0.01. For x = 0.025 only TI and TL are detected, while for x = 0.05 no transitions were observable. The values of TI and TL increase with x while TLT decreases and disappears at the concentration x = 0.025. The effect of defects, besides modifying the transition temperatures, is that of broadening and lowering the heat capacity anomaly at the lock-in transition until its total quenching for x = 0.05. No observable hysteresis is detected in this transition. NQR and x-ray diffraction data show the Inc–C transition up to the highest concentration. We conclude that this phenomenology is caused by weak interaction of the incommensurate modulation with point defects even in the region close to the Inc–C transition.
    No preview · Article · Nov 2002 · Journal of Physics Condensed Matter
  • Source
    By:Aleksandrova · IP (Aleksandrova · IP · Burriel · R (Burriel · Bartolome · J (Bartolome · Bagautdinov · BS (Bagautdinov · BS · [...] · AA · Torres · JM (Torres · JM · Vasiljev · AD (Vasiljev · AD · Solovjev · LA (Solovjev · LA ·
    [Show abstract] [Hide abstract] ABSTRACT: The trigonal (P-3 m1) modification of Cs3Bi2Br9 and Cs3Sb2I9 have been studied using NQR, X-ray single crystal and powder pattern methods. Moreover, the heat capacity was measured in a wide temperature interval: 4-300 K. In Cs3Bi2Br9 a second-order phase transition was found at T-C= 96 K. The low-temperature phase is monoclinic (C12/c1), with the unit cell doubled along the [001] direction. Cs3Sb2I9 has a sequence of phase transitions at T-C = 85 K, T-i = 78 K and T-L = 72.1 K. The mononclinic structure below 85 K is isomorphic with the low-temperature structure of Cs3Bi2Br9. According to calorimetric data the lock-in transition at 72.1 K is discontinuous.
    Full-text · Article · Aug 2002 · Phase Transitions
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    [Show abstract] [Hide abstract] ABSTRACT: The trigonal (P-3 m1) modification of Cs3Bi2Br9 and Cs3Sb2I9 have been studied using NQR, X-ray single crystal and powder pattern methods. Moreover, the heat capacity was measured in a wide temperature interval: 4–300 K. In Cs3Bi2Br9 a second-order phase transition was found at TC¼96 K. The low-temperature phase is monoclinic (C12/c1), with the unit cell doubled along the [001] direction. Cs3Sb2I9 has a sequence of phase transitions at TC¼85 K, Ti¼78K and TL¼72.1 K. The monoclinic structure below 85K is isomorphic with the low-temperature structure of Cs3Bi2Br9. According to calorimetric data the lock-in transition at 72.1K is discontinuous.
    Full-text · Article · Jun 2002 · Phase Transitions
  • Yu. N. Ivanov · A. A. Sukhovsky · I. P. Aleksandrova · J. Totz · D. Michel
    [Show abstract] [Hide abstract] ABSTRACT: The chemical exchange of deuterons in a partly deuterated ammonium hydrogen selenate crystal is investigated by deuteron magnetic resonance (2H NMR) spectroscopy over a wide range of temperatures. The changes observed in the line shape of the NMR spectra at temperatures above 350 K are characteristic of chemical exchange processes. The exchange processes are thoroughly examined by two-dimensional 2H NMR spectroscopy. It is established that, over the entire temperature range, only deuterons of hydrogen bonds are involved in the exchange and the rates of exchange between deuterons of all types are nearly identical. No deuteron exchange between the ND4 groups and hydrogen bonds is found. A new model of proton transport in ammonium hydrogen selenate is proposed on the basis of the experimental data. This model makes it possible, within a unified context, to explain all the available experimental data, including macroscopic measurements of the electrical conductivity.
    No preview · Article · Jun 2002 · Physics of the Solid State
  • J. Totz · D. Michel · Yu. N. Ivanov · AA Sukhovsky · I. P. Aleksandrova · J. Petersson
    [Show abstract] [Hide abstract] ABSTRACT: The microscopic mechanisms of proton transport in partially deuterated ammonium hydrogen selenate [NH4HSeO4 (AHSe)] and partially deuterated mixed crystals of betaine phosphate (DBP) and betaine phosphite (DBPI) (DBP1−xDBPIx) were studied by means of one-dimensional Fourier transform 2H NMR, two-dimensional (2D) 2H NMR and dielectric measurements. Slow chemical exchange processes of deuterons between different hydrogen bridges occur which can be studied by means of the 2D 2H NMR technique over a wide temperature range. In both systems, AHSe and DBP1−xDBPIx, the ionic conductivity is probably realized via jumps of the protons or deuterons between different hydrogen bonds (inter-bond jumps). The importance of certain defects for the conductivity process is clearly revealed. In AHSe, jumps occur through non-occupied hydrogen positions. In the mixed crystals DBP1−xDBPIx, the creation of defects is in fact favoured by the substitution of DBP for DBPI molecules or vice versa. The creation of vacancies may be explained by the occurrence of defects in the lattice structure, e.g. on the basis of the known Grotthuis mechanism and a multi-dimensional conductivity model as suggested for KDP. Copyright © 2001 John Wiley & Sons, Ltd.
    No preview · Article · Dec 2001 · Magnetic Resonance in Chemistry
  • Yu. N. Ivanov · A. A. Sukhovskii · V. V. Lisin · I. P. Aleksandrova
    [Show abstract] [Hide abstract] ABSTRACT: The phase transitions of Cs3Sb2I9, Cs3Bi2I9, and Cs3Bi2Br9crystals were investigated by 133Cs nuclear magnetic resonance. Cs3Bi2Br9was also studied by 87Br nuclear quadrupole resonance. The parameters of the Cs electric-field gradient tensors were determined. The phase transitions were shown to produce significant changes in the nearest neighbor environment of only one of two inequivalent Cs sites. In Cs3Sb2I9, the tensors remain axisymmetric below the transition at 85 K, in line with the assumption relying on powder x-ray diffraction data that, below the transition temperature, Cs3Sb2I9has a trigonal structure. The observed temperature variation in the shape of the 133Cs NMR and 127I NQR signals suggests that Cs3Bi2I9may undergo a transition to an incommensurate phase.
    No preview · Article · May 2001 · Inorganic Materials
  • Yu.N. Ivanov · A.A. Sukhovskii · V.V. Lisin · I.P. Aleksandrova
    [Show abstract] [Hide abstract] ABSTRACT: The phase transitions of Cs 3Sb 2I 9, Cs 3Bi 2I 9, and Cs 3Bi 2Br 9 crystals were investigated by 133Cs nuclear magnetic resonance. Cs 3Bi 2Br 9 was also studied by 87Br nuclear quadrupole resonance. The parameters of the Cs electric-field gradient tensors were determined. The phase transitions were shown to produce significant changes in the nearest neighbor environment of only one of two inequivalent Cs sites. In Cs 3Sb 2I 9, the tensors remain axisymmetric below the transition at 85 K, in line with the assumption relying on powder x-ray diffraction data that, below the transition temperature, Cs 3Sb 2I 9 has a trigonal structure. The observed temperature variation in the shape of the 133Cs NMR and 127INQR signals suggests that Cs 3Bi 2I 9 may undergo a transition to an incommensurate phase.
    No preview · Article · Jan 2001
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The atomic structure of Cs3Sb2I9 single crystals was refined using X-ray diffraction data (sp. gr. P3m1; wR = 1.58% and R = 3.07%). The phase transitions revealed earlier were found to be accompanied by the appearance of superstructural reflections. At T c1 = 86 K, the reflections indicating doubling of the c parameter. At T c2 = 73 K, a first-order phase transition takes place accompanied by “freezing” of the satellites h, k + 1/2, l + 1/2 reflections. In the temperature range from 73 to 78 K, an incommensurate phase providing the satellites h, k + 1/2 + δ, l + 1/2 is formed.
    Full-text · Article · Dec 2000 · Crystallography Reports

Publication Stats

515 Citations
77.37 Total Impact Points

Institutions

  • 1982-2005
    • Russian Academy of Sciences
      • Institute of Crystallography
      Moskva, Moscow, Russia
  • 1980-1981
    • University of Ljubljana
      • Department of Physics
      Lubliano, Ljubljana, Slovenia