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VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics Physics (September 4--7, 2006, Lviv, Ukraine)

This issue contains Proceedings of the VIII Ukrainian-Polish and III~East-European Meeting on Ferroelectrics Physics (Ukr-Pol 8) held in Lviv on September 4--7, 2006. The Meeting was the continuation of the common Polish-Ukrainian meetings devoted to various problems in physics of ferroelectrics and carried out earlier in Ustron-Zdrój (2004), Uzhgorod-Synjak (2002), Cracow (2000), Dnipropetrovsk (1998), Kudowa Zdrój (1996), Uzhgorod (1994), Wroclaw (1992) and Lviv (1990).

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Title: Radiation spectrum of an electron moving in a spiralin medium
Author(s):

	A.V.Konstantinovich (Fedkovych Chernivtsi National University, 2, Kotsyubinsky Str.,Chernivtsi, 58012, Ukraine) ,
	I.A.Konstantinovich (Fedkovych Chernivtsi National University, 2, Kotsyubinsky Str.,Chernivtsi, 58012, Ukraine) ,

The action of the Doppler effect on the particularities of radiation power spectral distribution of an electron moving in a spiral in a medium has been investigated near the Cherenkov threshold. The fine structure of the electromagnetic radiation spectrum at the Cherenkov threshold and the synchrotron-Cherenkov radiation spectrum for an electron moving along a spiral with non-relativistic longitudinal component of the velocity (i.e., the component parallel to the magnetic induction vector) in a transparent isotropic medium have been obtained and studied.

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Title: Phonon spectra of Cu₆PS₅Br superionic ferroelastic: experimental and theoretical studies
Author(s):

	I.P.Studenyak (Uzhgorod National University, Faculty of physics, 46Pidhirna Str., 88000 Uzhgorod, Ukraine) ,
	K.Z.Rushchanskii (Institute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyn St., 88000 Uzhgorod, Ukraine) ,
	R.Yu.Buchuk (Uzhgorod National University, Faculty of physics, 46Pidhirna Str., 88000 Uzhgorod, Ukraine) ,
	V.O.Stephanovich (Institute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyn St., 88000 Uzhgorod, Ukraine) ,

The anomalous temperature behavior of the Raman scattering bands at superionic phase transition of is revealed. Using density functional perturbation theory within local density approximation, ab initio long-wavelength phonons have been obtained for high-symmetry cubic structure. In the calculated phonon spectrum two unstable modes indicate the experimentally observed sequence of ferroelastic and superionic phase transitions.

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Title: Properties of interface phonon spectra in complicated cylindrical nanosystem
Author(s):

	O.M.Voitsekhivska (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho Str., Chernivtsi, 58012, Ukraine) ,
	A.M.Gryschyk (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho Str., Chernivtsi, 58012, Ukraine) ,

The spectra of two types of interface phonons (top and side optical) are studied within the framework of dielectric continuum model for combined nanoheterosystems consisting of semiconductor cylindrical quantum dots inside the cylindrical quantum wire placed into dielectric or semiconductor medium. The dependencies of both types of interface phonon energies on the quasiwave numbers and geometric parameters of nanosystem are calculated and analysed.

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Title: Exciton in closed and opened quantum dot
Author(s):

	M.V.Tkach (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho Str.,Chernivtsi, 58012, Ukraine) ,
	Ju.O.Seti (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho St.,Chernivtsi, 58012, Ukraine) ,

The theory of exciton spectrum in spherically symmetric states for the three- shell closed spherical quantum dot is proposed. The evolution of the exciton spectrum while varying the outer well thickness from zero (stationary spectrum of single closed spherical quantum dot) to infinity (quasistationary spectrum of a single open spherical quantum dot) is investigated. The mechanism of damping (semiwidth) of quasistationary states due to the redistribution over the energy levels of probability of exciton location in the space of two inner shells of nanosystem is studied. It is shown that the three shell closed spherical quantum dot of a rather big thickness of the outer well quite sufficiently and exactly reflects the basic properties of the quasistationary exciton spectrum in a single open spherical quantum dot.

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Title: Effect of hydrostatic pressure on structural and electronic properties of TGS crystals (first-principle calculations)
Author(s):

	B.Andriyevsky (Koszalin University of Technology, Faculty of electronics and computer sciences, 2 Sniadeckich Str., 75-453 Koszalin, Poland) ,
	W.Ciepluch-Trojanek (Koszalin University of Technology, Faculty of electronics and computer sciences, 2 Sniadeckich Str., 75-453 Koszalin, Poland) ,
	A.Patryn (Koszalin University of Technology, Faculty of electronics and computer sciences, 2 Sniadeckich Str., 75-453 Koszalin, Poland) ,

First principle calculations of the effect of hydrostatic pressure on the structural and electronic parameters of TGS crystals have been carried out within the framework of density functional theory using the CASTEP code. The volume dependence of total electronic energy E(V) of the crystal unit cell satisfies the third-order Birch-Murnaghan isothermal equation of state. For the pressure range of -5...5 GPa, the bulk modulus was found to be equal to K=45 ± 5 GPa. The relative pressure changes of the unit cell parameters were found to be linear in the range of -5...5 GPa. Crossing of the pressure dependencies of enthalpy corresponding to the ferroelectric and non-ferroelectric phases at P=7.7 GPa testifies to the probable pressure induced phase transition in TGS crystal.

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Title: The band energy structure of RbKSO₄ crystals
Author(s):

	O.V.Bovgyra (Franko Lviv National University, Kyrylo and Mefodij, 8str., Lviv, 79005 Ukraine) ,
	V.Yo.Stadnyk (Franko Lviv National University, Kyrylo and Mefodij, 8str., Lviv, 79005 Ukraine) ,
	A.V.Franiv (Franko Lviv National University, Kyrylo and Mefodij, 8str., Lviv, 79005 Ukraine) ,
	M.R.Tuzyak (Franko Lviv National University, Kyrylo and Mefodij, 8str., Lviv, 79005 Ukraine) ,
	O.Z.Chyzh (Franko Lviv National University, Kyrylo and Mefodij, 8str., Lviv, 79005 Ukraine) ,

The energy band structure of mechanically free and compressed RbKSO₄ single crystals is investigated. It is established that the top of the valence band is located at the D point of the Brillouin zone [k = (0.5, 0.5, 0)], the bottom of the conduction band lies at the Γ point, and the minimum direct band gap E_g is equal to 5.80 eV. The bottom of the conduction band is predominantly formed by the K s, Li p, Rb s, and Rb p states hybridized with the S p and O p antibonding states. The pressure coefficients of the energy position of the valence and conduction band states and the band gap E_g are determined.

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Title: The baric changes of the refractive properties of K₂SO₄ crystals
Author(s):

	V.Yo.Stadnyk (Franko Lviv National University, Kyrylo and Mefodij, 8Str., Lviv, 79005 Ukraine) ,
	M.O.Romanyuk (Franko Lviv National University, Kyrylo and Mefodij, 8Str., Lviv, 79005 Ukraine) ,
	O.Z.Chyzh (Franko Lviv National University, Kyrylo and Mefodij, 8Str., Lviv, 79005 Ukraine) ,
	V.F.Vachulovych (Franko Lviv National University, Kyrylo and Mefodij, 8Str., Lviv, 79005 Ukraine) ,

The dependencies of the birefringence Δn_i of K₂SO₄ crystals in wide spectral (250-800 nm) ranges, as well as the effect of uniaxial mechanical stresses on them have been studied. The values of n_i for K₂SO₄ are found to be rather sensitive to the uniaxial stress. The spectral characteristics of the refractive indices n_i of free and mechanically clamped K₂SO₄ crystals have been studied. The refractive indices turned out to decrease under the effect of uniaxial stress. The variations in the refraction, electron polarizability and the position of the center of the effective ultraviolet absorption band have been calculated. It is shown that the positions of the isotropic points in these crystals can be controlled by thermal and spectral methods.}

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Title: Electret effect in intercalated crystals of the A^IIIB^VI group
Author(s):

	I.Grygorchak (Lviv Polytechnic National University, 12 Bandera Str., 79013 Lviv, Ukraine) ,
	S.Voitovych (Lviv Polytechnic National University, 12 Bandera Str., 79013 Lviv, Ukraine) ,
	I.Stasyuk (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine) ,
	O.Velychko (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine) ,
	O.Menchyshyn (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine)

Measurements of dielectric properties of Ni-intercalated GaSe and InSe have been performed. The present study is aimed at the investigation of the low-admixture region where the intercalation induced electret effect occurs. The effect exhibits pronounced peak-like concentration dependences and a non-monotonous temperature behaviour with maximum magnitudes at low temperatures. Intercalation leads to over tenfold increase of dielectric permittivity over the whole measured frequency range with up to several orders at low frequencies for GaSe. Temperature dependences of the permittivity demonstrate well-defined peaks with localizations and heights strongly depending on the concentration. A microscopic model of order-disorder type has been proposed that considers redistribution of intercalant atoms between non-polar octahedral and polar tetrahedral positions in the crystal van der Waals gaps. Such a redistribution can occur in the form of phase transition to the polar phase (corresponding to the electret effect) which is stabilized by the internal field. For the case of octahedral positions being more preferable, the model predicts a peak-like dependence of the crystal polarization on chemical potential due to passing through the interjacent polar phase in accordance with the measured behaviour of the electret effect. The calculated temperature dependences of dielectric susceptibility qualitatively reproduce experimental results for permittivity as well.

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Title: Electron energy spectrum in core-shell elliptic quantum wire
Author(s):

	V.Holovatsky (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho St.,Chernivtsi, 58012, Ukraine) ,
	V.Gutsul (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho St.,Chernivtsi, 58012, Ukraine) ,

The electron energy spectrum in core-shell elliptic quantum wire and elliptic semiconductor nanotubes are investigated within the effective mass approximation. The solution of Schrodinger equation based on the Mathieu functions is obtained in elliptic coordinates. The dependencies of the electron size quantization spectrum on the size and shape of the core-shell nanowire and nanotube are calculated. It is shown that the ellipticity of a quantum wire leads to break of degeneration of quasiparticle energy spectrum. The dependences of the energy of odd and even electron states on the ratio between semiaxes are of a nonmonotonous character. The anticrosing effects are observed at the dependencies of electron energy spectrum on the transversal size of the core-shell nanowire.

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Title: Electron and hole spectra in quantum wire with two quantum dots in the electric field
Author(s):

	O.Makhanets (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho Str.,Chernivtsi, 58012, Ukraine) ,
	A.Gryschyk (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho Str.,Chernivtsi, 58012, Ukraine) ,
	M.Dovganiuk (Fedkovych Chernivtsi National University, 2, Kotsyubinskoho Str.,Chernivtsi, 58012, Ukraine) ,

The energy spectrum of electron and hole is investigated in a complicated nanoheterosystem consisting of two cylindrical semiconductor quantum dots placed into semiconductor quantum wire. Quantum dots are separated by barrier-layer, which is under the action of a constant electric field. The dependencies of electron and hole energies on geometric parameters of quantum dots and electric field intensity are analysed.

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Title: EPR and dielectric spectroscopy of reorienting Cr³⁺-Li⁺ pair centres in Li₂Ge₇O₁₅crystal
Author(s):

	M.D.Volnianskii (Department of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, Dnipropetrovsk 49050, Ukraine.) ,
	M.P.Trubitsyn (Department of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, Dnipropetrovsk 49050, Ukraine.) ,
	Yahia A.H. Obaidat (Department of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, Dnipropetrovsk 49050, Ukraine.) ,

Earlier it has been shown that in the lithium heptagermanate Li₂Ge₇O₁₅ structure the chromium doping ions substitute the germanium hosts and create Cr³⁺-Li⁺ pair centres. In the paper EPR and dielectric spectra of Li₂Ge₇O₁₅:Cr³⁺ crystal are studied in the temperature range $300\div 500$ K. The thermally activated reorientation of Cr³⁺-Li⁺ pairs has been detected through EPR line width broadening and dielectric relaxation. Key words: impurity ions, electron paramagnetic resonance, dielectric loss and relaxation

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Title: On a correlation between EPR data for SASeD doped with Cr³⁺ and soft modes
Author(s):

	I.E.Lipinski (Institute of Physics, Szczecin University of Technology, Aleja Piast\'ow 17, 70--310 Szczecin, Poland) ,
	J.Kuriata (Institute of Physics, Szczecin University of Technology, Aleja Piast\'ow 17, 70--310 Szczecin, Poland) ,
	N.A.Korynevskii (Institute of Physics, Szczecin University of Technology, Aleja Piast\'ow 17, 70--310 Szczecin, Poland; Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, Svientsitskii 1., 79011Lviv, Ukraine; Institute of Physics, University of Szczecin, Wielkopolska 15., 70--451 Szczecin, Poland) ,

PR experimental results obtained for SASeD doped with Cr³⁺ are reported with special emphasis on those observations which reveal the effect of soft modes i.e. the temperature dependence of the D_ZZ spin-Hamiltonian parameter and the temperature dependence of the EPR linewidth. An extension of the two-sublattice model, previously developed and tested for SASD, to include lattice vibrations is presented. The obtained spectrum of bound excitations for the system investigated supports the idea that soft modes contribute to the phase transition at T_C = 175 K. The anomaly detected at T₁ =150 K has only a quasisoft mode character and the anomaly detected at T₂ = 280 K cannot be related to the effect of soft modes.

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Title: Pyroelectric response of inhomogeneous ferroelectric-semiconductor films
Author(s):

A.N.Morozovska (V.Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,pr. Nauki 41, 03028 Kiev, Ukraine) ,

We have modified Landau-Khalatnikov approach and shown that the pyroelectric response of inhomogeneous ferroelectric-semiconductor films can be described by using six coupled equations for the average displacement, its mean-square fluctuation and correlation with charge defects density fluctuations, average pyroelectric coefficient, its fluctuation and correlation with density fluctuations of charged defects. Coupled equations demonstrate the inhomogeneous reversal of pyroelectric response in contrast to the equations of Landau-Khalatnikov type, which describe the homogeneous reversal with sharp pyroelectric coefficient peaks near the thermodynamic coercive field values. Our approach explains pyroelectric loops observed in Pb(Zr,Ti)O₃ film.

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Title: Dielectric properties of CuInP₂S₆ crystals under high pressure
Author(s):

	V.S.Shusta (Uzhhorod National University, 54 Voloshyn St., 88000 Uzhhorod, Ukraine) ,
	I.P.Prits (Uzhhorod National University, 54 Voloshyn St., 88000 Uzhhorod, Ukraine) ,
	P.P.Guranich (Uzhhorod National University, 54 Voloshyn St., 88000 Uzhhorod, Ukraine) ,
	E.I.Gerzanich (Uzhhorod National University, 54 Voloshyn St., 88000 Uzhhorod, Ukraine) ,
	A.G.Slivka (Uzhhorod National University, 54 Voloshyn St., 88000 Uzhhorod, Ukraine) ,

Dielectric properties of CuInP₂S₆ layered crystals in the range of ferrielectric phase transition are studied under hydrostatic pressure. The pressure dependence of the phase transition temperature testifies to the phase transition being of the order/disorder type. The (p,T) phase diagram of CuInP₂S₆ crystals has been constructed.

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Title: Dynamics of the domain structure in non-uniform ferroelectric crystals
Author(s):

	K.Matyjasek (Institute of Physics, Szczecin University of Technology, Al. Piastow 48,70--310 Szczecin, Poland) ,
	R.Rogowski (Institute of Physics, Szczecin University of Technology, Al. Piastow 48,70--310 Szczecin, Poland) ,

This work presents a study of the domain reversal characteristics related to the internal bias field in non-uniform telluric acid ammonium phosphate (TAAP) crystal. We have shown that there is a direct connection between the defective structure of the crystal and stretched exponential polarization relaxation in ferroelectric crystals. The domain switching was studied by means of the nematic liquid crystal decoration technique.

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Title: X-ray photoelectron spectra and electronic structure of quasi-one-dimensional SbSeI crystals
Author(s):

	J.Grigas (Faculty of Physics, Vilnius University, Sauletekio 9/3, LT--10222 Vilnius, Lithuania) ,
	E.Talik (Institute of Physics, Silesian University,Universytetska 4, 40--007 Katowice, Poland) ,
	M.Adamiec (Institute of Physics, Silesian University,Universytetska 4, 40--007 Katowice, Poland) ,
	V.Lazauskas (Institute ofTheor. Phys. and Astronomy, Vilnius University, Gostauto 12,LT--01108 Vilnius, Lithuania) ,

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels from the (110) and (001) crystal surfaces for the quasi-one-dimensional high permittivity SbSeI single crystal isostructural to ferroelectric SbSI. The XPS were measured with monochromatized Al Ka radiation in the energy range of 0-1400 eV at room temperature. The VB is located from 1.6 to 20 eV below the Fermi level. Experimental energies of the VB and core levels are compared with the results of theoretical ab initio calculations of the molecular model of the SbSeI crystal. The electronic structure of the VB is revealed. Shifts in the core-level binding energies of surface atoms relative to bulk ones, which show a dependency on surface crystallography, have been observed. The chemical shifts of the core levels (CL) in the SbSeI crystal for the Sb, I and Se states are obtained.

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Title: Phase transitions in KDP crystals with the complex organic and inorganic impurities
Author(s):

	B.Strukov (Lomonosov Moscow State University, Moscow, Russia, 119992) ,
	I.Shnaidshtein (Lomonosov Moscow State University, Moscow, Russia, 119992) ,
	S.Grabovsky (Lomonosov Moscow State University, Moscow, Russia, 119992) ,

In this paper we present the results of the study of dielectric and thermal properties of KDP crystals doped with different complex organic and inorganic molecules which decorate different (pyramidal or prismatic) crystal growth sectors. It is shown that the properties of stained and transparent parts of the crystal in comparison with the corresponding parts of the nominally pure crystal are different for KDP crystals grown by means of traditional (slow) and rapid growth technique. The difference of the domain contribution into dielectric constant of the polar phase and its characteristic hysteresis in pure and dyed crystals, transition temperature position, form of the specific heat anomaly are presented and analyzed. The most probable model of incorporation of the complex impurity molecules into KDP structure is proposed.

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Title: The 60th anniversary of Ivan Vakarchuk

Professor Ivan Vakarchuk is a well-known Ukrainian physicist internationally recognized among theoreticians owing to his works on quantum liquids, phase transitions and critical phenomena, disordered systems and quantum mechanics. Being the author of 230 scientific papers and 5 textbooks, he is widely known for having developed various approaches and techniques in theoretical studies of many-particle quantum systems as well as a brilliant lecturer in theoretical physics.

Title: VII^th School-Seminar for Young Scientists in Statistical Physics and Condensed Matter Theory

On May 31-June 1 the seventh school-seminar for young scientists will take place at the Institute for Condensed Matter Physics. During the school-seminar, the prominent Ukrainian scientists will give their lectures in the field of statistical physics and condensed matter theory. We are pleased to invite all young scienstists up to 35 years of age as well as students and PhD students to take part in the work of our school-seminar. All the participants will have an opportunity to present and discuss the results of their investigations as well as to establish friendly relations with colleagues from different regions of Ukraine. To participate one should fill in the registration form on a school-seminar web-site and send an abstract. Most interesting and actual presentations will be awarded.

Within the framework of the school-seminar the annual awards for young scientists working in the field of statistical physics and physics of condensed matter will be presented. The competition was established in 2001 and is devoted to the foundation anniversary of the first Institute department i.e., the Department for Statistical theory of Condensed Systems in May of 1969. Traditionally, the school-seminar is organized by the Council of Young Scientists and Directorate of the Institute for Condensed Matter Physics.

This event is supported by Department of Physics and Astronomy of the National Academy of Sciences of Ukraine.

The list of required documents and application forms as well as additional information can be found on our website. Working language of the school-seminar is Ukrainian. Please register and send your applications before May 1, 2007.

Address for contacts:
Council of Young Scientists Institute for Condensed Matter Physics,
1 Svietsitskii Street, 79011 Lviv, Ukraine;
E-mail: cys@icmp.lviv.ua
Web-page: http://www.icmp.lviv.ua/konkurs/
Phone: +38 0322761978; Fax: +38 0322761158

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Title: To the memory of Yuri Rudavskii

On February 21, 2007 a sudden regrettable death took away Yuri Rudavskii, a renowned Ukrainian scientist in the field of theoretical physics, doctor of physics and mathematics, professor, head of the Chair of higher mathematics, Rector of Lviv Polytechnic National University.