Solid State Phenomena Vol. 112

Abstract: There are two kinds of structural transformations in the crystalline solid state: solid state reactions, in which the product chemically different from the starting material can be isolated, and polymorphic transitions, when the phases have different organization of identical molecules in the crystal structures. As a consequence, the starting and the final phases of a solid state reaction differ in the melt and vapor, while different polymorphic modifications are identical in melt or gas phase. Some examples of the different phase transitions in the solid state are described in detail: the π-molecular complexes, the hydrogen-bond transformations and the reversible single crystal - twin transition.

Abstract: We review recent progress of theoretical studies for the photoinduced phase tran- sitions (PIPTs) to clarify what the PIPTs are. There are two types of the PIPTs: (a) global change via optically excited states and (b) new material phase creation in optically excited states. First, concerning (a), photoinduced structural phase transitions via excited electronic states are discussed using a minimal one-dimensional model composed of localized electrons and lattices. We show that the global structural change by photoexcitation only at a single site is possible under the adiabatic or diabatic approximation. This dynamics of the domain bound- aries (domain walls) is called the “photoinduced domino process,” which is the photoinduced nucleation in nonequilibrium first-order phase transition. Second, concerning (b), we discuss quantum orders of electron-hole (e-h) systems, which are optically excited states of insulators consisting of many electrons and holes in two bands. In particular, the “exciton Mott transi- tion,” i.e., the “from-insulator-to-metal” transition of the e-h systems as the particle density increases is introduced. We stress that this transition depends strongly on dimensionality of the system.

Abstract: The work is a review paper concerning application of neutron diffraction methods for condensed matter investigations and for characterizing modern materials, namely for crystal and magnetic structures determination, small-angle scattering, investigations of chemical reactions and some practical applications. It addresses briefly a few of more prominent techniques that are important for materials scientists. In the first part of the work information on the methods and ways of interpretation of obtained results is given. Then the results for some chosen compounds are presented.

Abstract: This paper gives a review about the current state of the art in neutron imaging like neutron radiography, neutron tomography, stroboscopic imaging and phase contrast imaging. The different techniques are described and compared to X-rays.

Abstract: We investigated the thermo- and photo-induced phase transitions between low spin (LS) and high spin (HS) states of the molecular crystal of [Fe(PM-BiA)2(NCS)2] in the orthorhombic form, by using X-ray diffraction. The structure of the photoinduced HS state, generated from the LS state at low temperature, is compared to the structures of the HS and LS phases at thermal equilibrium and to the thermally trapped HS state. The preliminary results presented here show that the structural reorganization is similar in the different HS states.

Abstract: Influence of the OH group position in the molecule on solid state polymorphism was found. Dynamics in solid phases of two dimethyl butanols were studied by inelastic incoherent neutron scattering. In glass of plastic crystal the boson peak was detected.

Abstract: The low-temperature inelastic incoherent neutron scattering spectrum of norethisterone was compared with that calculated by the density functional theory method. The quantum chemical calculations permitted proposing the assignment of the vibrational modes. In particular, the dynamics of the methyl group substituted at C(13) of the steroid skeleton was analysed on the basis of the neutron scattering spectra and temperature dependence of the spin-lattice relaxation time (1H NMR).

Abstract: The thermal-driven evolution of stripe domain structures in ultrathin magnetic films is analyzed with regard to temperature dependencies of the film magnetic parameters. In the vicinity of the Curie temperature or points of the spin reorientation the equilibrium stripe domain period was found to exponentially decrease with increasing temperature. It is shown that the temperature dependence of the characteristic length is the key parameter controlling the domain period changes. Irreversible and reversible changes of the domain period as well as the so-called inverse domain melting are discussed.

Abstract: A generalized model of a solid-solid interface is built. The model takes into account additional surface mass densities on both sides of the interface and an anisotropic and/or anharmonic coupling potential. The resonances due to the potential (up to three) manifest themselves by minima (zeros) of transmition and/or extrema in reflected and transmitted waves of different polarization depending on physical properties of the media and of the geometry.