Thermoanalytical properties and structure of (As2Se3)100 − x(Sb2Se3)x glasses by Raman and 77Se MAS NMR using a multivariate curve resolution approach

International audienc

Intrinsic defect states and electron spin resonance in the Ge-S bulk glasses

A review of electron paramagnetic resonance (ESR) of bulk glassy Ge-S system is presented. The long-range periodicity in amorphous materials and glasses is disturbed by the fluctuations of bond angles, bond lengths and by composition as well. In a limit case an increase of the bond lengths can break chemical bonds between atoms of glass and so-called dangling bonds are formed. These are singly occupied and thus paramagnetic if stabilized by lowering of Hubbard´s energy. The dangling bonds in chalcogenide glasses and their relation to the ESR spectra are still questionable. Dangling bonds however can interact with nearest atoms of glass and create another type of multiatomic defect centers which are still paramagnetic. This review can also help to solve the problem why in the whole class of chalcogenide glasses the so-called dark ESR signal is found in Ge-S glasses only

Contribution to the study of some materials

V první části práce jsou shrnuty výsledky studia skel systému ge-S pomocí elektronové paramagnetické rezonance a fotolumuniscence.V druhé části jsou uvedeny výsledky získané při použití některých metod termické analýzy při studiu řady nekrystalických materiálů. vedle toho je ukázána také možnost aplikace těchto metod při studiu dehydratace interkalátu VOPO42H2O.Presented habilitation thesis contains two parts. The first one deals with the study of intrinsic defect centers of semiconducting Ge-S glassy system. The result of this part is the proposal of new model of intrinsic paramagnetic defects. The Ge-related signal was found in glasses of whole glass-forming region. This signal was assigned to a two-atomic defect center which is formed by the interaction of broken bonds of Ge with two-coordinated sulfur atoms forming (Ge4...S3)o centers. A multiline spectrum was found not only in Ge-S sulfur rich glasses but also in glassy sulfur after excitation by Ar+ laser. This signal can be assigned to two defect centers: (S2...trans-S3)o and (S2...cis-S3). On the basis of this model is possible to explain non-occurrence of similar paramagnetic defect centers in other chalcogenide glassy systems (for example Ge-Se, As-S, As-Se) as well. The second part concerns with thermoanalytical properties of materials. Kinetic of both isothermal and non-isothermal crystallization was studied by Differential scanning calorimetry for undercooled melts of selenium and As-Se system. Influence of Johnson, Mehl, Avrami kinetic exponent n on determination of the proper kinetic model was demonstrated. Application of Differential scanning calorimetry, Thermogravimetry, Thermomechanical analysis and Dynamic differential scanning calorimetry on thermal stability of materials (for example glasses, crystals, intercalates) was used.Dokončená práce s úspěšnou obhajobo

Příprava a elektrické, optické a magnetické vlastnosti polovodivých skel systému Ge-S dotovaných vanadem

Dokončená práce s úspěšnou obhajobo

High temperature dynamical thermomechanical analysis

DTMA was used for measurements of NBS 711 model glass. Results were compared with measurement of DSC, TMA and viscosity

Thermal properties of glassy system of As-S in area of glass transformation

Glasses of As-S system were studied in the glass transition region. StepScan method was used for measuring of heat capacity. Difference of enthalpy H and difference of entropy S were calculated as well

Using of dynamic thermomechanical analysis for study of glasses

Model NBS 711 glass was used for DTMA and DSC measurement Realx and imahinary part of modulus