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Information × Registration Number 0202U000223, 0199U000670 , R & D reports Title Investigation of external fields and disorder influence on phase transition and physical properties of pseudospin systems with essential short range and long range correlations popup.stage_title Head Levyts'kyj R.R., Registration Date 01-02-2002 Organization Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine popup.description2 The report includes 218 pages of text. It consists of an introduction, ten sections of main part, conclusions, bibliography of 180 references and one appendix. There are 94 figures and 6 tables in the report.Key words: regularly alternating XY model, spin-Pierls dimerisation, Ising model, two-level atoms, anisotropic fluid, electric field, Blume-Emery-Griffits model, reentrant phase transition, hydrogen bonded ferroelectrics, tunneling, hydrostatic pressure, shear stressSubjects of investigations: hydrogen bonded ferroelectrics, anisotropic fluids, Ising model, Blume-Emery-Griffits model, XY model Task of work was: was to develop mathematical methods to i investigation of regular and disordered pseudospin systems, construct a mathematical theory of relaxational phenomena and thermodynamic properties of such systems, to obtain an adequate description of the physical properties of concrete materials at changing external parameters (temperature, field, pressure).Influence of diagonal disorder on thermodyn amics of regularily alternating one-dimensional XY model and its local magnetic properties was studies. Influence of correlated disorder on the chain thermodynamics was explored. For non-uniform fluid of two-level atoms in external electric field, the temperature dependence of surface tension and dependence of nucleation barrier on density of saturated vapour were obtained. Influence of magnetic or electric field on behavior of anisotropic fluids was studied. Conditions of orientational ordering in the system were explored. To calculate correlation functions and unary distribution functions of anisotropic fluids in external fields that can induce different types of symmetry, the integral equations method was developed. A series of approximations for the effective field methods was considered and extended to the Ising model with an arbitraty type of interactions. Dependence of the interaction type on thermodynanic an dynamic properties of the model was investigated. In the two-particle cluster approximation, the cascades of the reentrant and double-reentrant phase transitions for the BEG model on a simple cubic lattice were studied. Phase diagrams were consturcted and temperature dependences of dipole and quadrupolar moments were obtained. Influence of external magnetic field on thermodynamic properties of spin-1 Ising model with bilinear and quadrupolar interactions were studied. Influence of external pressures that do not lower the crystal symmetry on deuterated ferroelectrics and antiferroelectrics of the KDP family was explored. A universal dependence of the transition temperature in these crystals on D-site distance was revealed. In the proton ordering model for the KDP type crystals, the effects related to the shear strain e6 were taken into account. Temperature peculiarities of the corresponding elastic and piezoelectric characteristics of the crystals were described. Influence of shear stresses s6 (and the electric field directed along the axis с) and s1-s2 on the phase transition and physical character istics of the KDP family crystals was investigated. It was shown that the stress s1-s2 can induce in the crystals a new paraelectric phase of monoclinic symmetry. Thermodynamic and dielectric properties of KH2PO4 type ferroelectrics and NH4H2PO4 type antiferroelectrics were studied with taking into account tunneling. In the cluster approximation, the components of static dielectric susceptibility tensor were calculated . Product Description popup.authors popup.nrat_date 2020-04-02 Close