National Repository of Grey Literature 61 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Preparation and characterization of novel molecular materials for nonlinear optics
Mathauserová, Jana ; Němec, Ivan (advisor) ; Nižňanský, Daniel (referee)
The main issue of this bachelor thesis is the investigation of salts and cocrystals of biuret and 2-aminopyrimidine in consideration of their usage in the field of nonlinear optics. The first attempt of this thesis was preparation of compounds combining biuret with organic or inorganic acids, urea and biguanide. The second part is focused on the searching of new salts of 2-aminopyrimidine and on further characterisation of its formerly prepared compounds. The methods employed to investigate the prepared materials include vibrational spectroscopy and X-ray diffraction analysis. The theoretical quantum mechanical calculations were used to predict the nonlinear optical properties of selected molecules and also for the interpretation of the recorded vibrational spectra. Measurements of second harmonic generation efficiency of selected powder samples were performed.
Novel prospective materials for nonlinear optics
Votrubcová, Iveta ; Němec, Ivan (advisor) ; Nižňanský, Daniel (referee)
This bachelor thesis is focused on the preparation of novel materials for nonlinear optics and includes studies of twenty-eight crystallization systems, which provide twelve crystalline compounds - salts of 2-aminopyrimidine and 2,4,6-triaminopyrimidine with inorganic oxo-acids (nitric, perchloric, sulfuric, phosphoric, phosphorous). Studied materials have been identified and defined by a vibrational spectroscopy and X-ray structure analysis. From the prepared materials only aminopyrimidinium (1+) hydrogen phospite fulfils the symmetry conditions for the second harmonic generation. Efficiency of the second harmonic generation was afterwards defined for the powdered sample relatively to the KDP and urea standards.
Magnetic nanoparticles and nanocomposites with spinel structure, their preparation and characterization
Holec, Petr ; Nižňanský, Daniel (advisor) ; Šubrt, Jan (referee) ; Sedmidubský, David (referee)
This work presents the preparation and physical properties of spinel nanoparticles and nanocomposites. All nanocomposites in diamagnetic matrix like chromites CoCr2O4, CuCr2O4, NiCr2O4, ZnCr2O4 and ferrite MgFe2O4 were prepared using sol-gel method. On the other hand, isolated nanoparticles such as MgCr2O4, MnCr2O4, CuCr2O4, NiCr2O4, and FeCr2O4, were prepared using autocombustion a co-precipitation methods. CoFe2O4 and MgFe2O4 were prepared by microemulsion alkoxide method. This microemulsion method was used for the spinel nanoparticles preparation for the first time. This work describes the influence of heat treatment temperature on the final particle size and influence of particle size on physical properties of material. The study of the influence of twovalent cationt in the spinel structure on the magnetic properties of chromites was also carried out. The final samples were characterized by XRD powder diffraction, Mössbauer spectroscopy, infrared and Raman spectroscopy, and HRTEM. The dependence of magnetization on applied magnetic field at constant temperature and ZFC (zero-field cooling) - FC (field cooling) measurement was carried out on the prepared sample.
Sol-gel synthesis of ternary ZnxTiyOz nanostructures for applications in solar cell technologies and photonics
Mrázek, Jan ; Nižňanský, Daniel (advisor) ; Pinkas, Jiří (referee) ; Pollert, Emil (referee)
The presented study deals with the sol-gel synthesis of nanocrystalline ternary phases of the general formula ZnxTiyOz, their characterization and potential application in photonics. Achieved results brings new fundamental knowledge about the processes leading to the formation of ZnxTiyOz nanocrystals from amorphous xerogels and gives novel information about structural and opto-electrical properties of prepared materials. Based on the presented results, most of all up-to-date reported ZnxTiyOz compounds with tailored nanocrystalline size and structure can be prepared as powders or thin films. Two sol-gel approaches based on the cluster process and direct heteronucleation were employed to prepare initial sol. Sols were optionally doped by Eu3+ ions to evaluate the effects of rare earth element to crystallization properties of formed compounds. In the first part of our study crystallization properties and structural evolution of thermally treated xerogels were analyzed. As a result a versatile method allowing the preparation of inverse spinel Zn2TiO4, cubic defect spinel ZnTiO3 and rhombohedral ZnTiO3 with tailored nanocrystal sizes was established. Initial composition and thermal annealing allow us to prepare selected ternary phase with tailored nanocrystal size ranging from tens of nanometers up to...

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