Miran Čeh

CeO2 thin films obtained by sol–gel deposition and annealed in air or argon

Abstract Thin films of CeO 2 were prepared on SnO 2 /F-coated glass plates by the sol–gel dip-coating process using CeCl 3 ·7H 2 O as a precursor. The films were heat-treated in an air or argon atmosphere. The structural, electrochemical and optical properties of these films depend on the preparation conditions. Transmission electron microscopy (TEM) showed the films to be polycrystalline with randomly orientated crystallised domains of up to 10 nm in size. The degree of crystallinity of films heat-treated in argon is higher than that of those heat-treated in air, and therefore their charge capacity values (15.9 mC cm −2 after 100 cycles) and reversibility of the ion-storage process (0.99 after 100 cycles) are higher than for films heat-treated in air (10.5 mC cm −2 and 0.86 after 100 cycles, respectively). Both films are optically passive under Li + ion insertion and have high optical transmittance (>80%).

Highly Efficient TiO2-Based Microreactor for Photocatalytic Applications

A photocatalytic, TiO2-based microreactor is designed and fabricated on a metal-titanium foil. The microchannel is mechanically engraved in the substrate foil, and a double-layered TiO2 anatase film is immobilized on its inner walls with a two-step synthesis, which included anodization and a hydrothermal treatment. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirm the presence of an approximately 10-μm-thick layer of titania nanotubes and anatase nanoparticles. The SEM and transmission electron microscopy (TEM) of the cross sections show a dense interface between the titanium substrate and the TiO2 nanotubes. An additional layer of TiO2-anatase nanoparticles on the top of the film provides a large, photocatalytic surface area. The metal-titanium substrate with a functionalized serpentine channel is sealed with UV-transparent Plexiglas, and four 0.8-mW UV LEDs combined with a power controller on a small printed-circuit board are fixed over the substrate. The photocatalytic activity and the kinetic properties for the degradation of caffeine are provided, and the longer-term stability of the TiO2 film is evaluated. The results show that after 6 months of use and 3600 working cycles the microreactor still exhibits 60% of its initial efficiency.

Polytype induced exaggerated grain growth in ceramics

In polycrystalline materials we frequently observe exaggerated growth of some grains. One of the reasons for such growth irregularity, which we describe here, is the formation of polytypic sequences within the affected grains. We present an atomic-level study of the polytypic faults that are found in sintered perovskite ceramics with various oxide additions. Grains containing polytypic faults grow preferentially along the direction of fault planes. Results from this study indicate that both the local structure and chemistry of these faults are intimately related to the host crystal and the secondary phase that exists between the main phase and the additive.

Thick film humidity sensors based on (Ba,Sr)TiO3 porous ceramic doped with MgO and CaO

Abstract Undoped and CaO or MgO doped Ba 0.5 Sr 0.5 TiO 3 materials for humidity sensors were investigated. Sensing elements were prepared in bulk in thick film form. The response of bulk samples, when measured at 400 Hz, was four orders of magnitude for doped and three orders of magnitude for undoped material. The dependence of conductance versus relative humidity for thick film sensors is around one order of magnitude less because of decrease in sensitivity under 40% relative humidity. This is attributed to the deficiency of pores with diameter under 30 nm which is presumably the result of the interaction between the sensing material and the glass phase in Pt electrodes.

Solubility of CaO in CaTiO3

The solubility and mode of incorporation of CaO in CaTiO3 were studied by X-ray powder diffraction, scanning and transmission electron microscopy, electron probe microanalysis and equilibrium electrical conductivity measurements. The presence of Ca4Ti3O10 in samples containing > 0.3 mol% excess CaO was confirmed by direct microscopic examination. Measurements of the equilibrium electrical conductivity showed no detectable shift in the conductivity profile for CaO-excess CaTiO3, thus setting an upper limit of 100 p.p.m. for the solubility of CaO in CaTiO3. The excess CaO is incorporated into CaTiO3 by formation of Ruddlesden-Popper type planar faults, which are layers of CaO coherently intergrown with CaTiO3. Ordering of these planar faults leads to the formation of the stable compound Ca4Ti3O10.

Formation of ruddlesden-popper faults and polytype phases in SrO doped SrTiO3

The formation of so-called Ruddlesden–Popper planar faults was studied in SrO-doped SrTiO 3 for different quantities of SrO additions and sintering conditions. For small SrO additions we observed a microstructure with a uniform grain size distribution and the enrichment of SrO at the grain boundaries. Larger additions of SrO produced a microstructure of elongated grains containing random planar faults, polytypic lamellae of more or less ordered faults, and polytype loops within SrTiO 3 grains. We showed that these SrTiO 3 grains were elongated as a result of preferential growth of the polytypic lamellae. In addition, we discuss a correlation between the formation of planar faults embedded in the perovskite matrix at low firing temperatures and Ruddlesden–Popper phases that are stable at higher temperatures.

The Synthesis of Anatase Nanoparticles and the Preparation of Photocatalytically Active Coatings Based on Wet Chemical Methods for Self-Cleaning Applications

We report on an improved sol-gel method for the production of highly photocatalytic titanium dioxide (TiO2) anatase nanoparticles which can provide appropriate control over the final characteristics of the nanoparticles, such as particle size, crystallinity, crystal structure, morphology, and also the degree of agglomeration. The synthesized anatase nanoparticles were characterized using various techniques, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and were tested in coatings for self-cleaning glass and ceramic surfaces. The coatings were prepared using a soft chemistry route and are completely transparent to visible light and exhibit a high photocatalytic effect, which was determined by contact-angle measurements. Finally, it is worth mentioning that both the sol-gel synthesis method and the coating-preparation method are based on a wet chemical process, thus presenting no risk of handling the TiO2 anatase nanoparticles in their potentially hazardous powder form at any stage of our development. Low-price, easy-to-handle, and nontoxic materials were used. Therefore, our work represents an important contribution to the development of TiO2 anatase nanoparticle coatings that provide a high photocatalytic effect and can thus be used for numerous applications.

Compositional Homogeneity of Ferroelectric (Pb,La)(Ti,Zr)O-3 Thick Films

Quantified wavelength dispersive spectroscopy (WDS) x-ray element maps were used to characterize active (Pb,La)(Ti,Zr) O 3 (PLZT) layers on Pt/PLZT/Al 2 O 3 substrates, one fired at 1050 °C and the other at 1150 °C. In the layer fired at 1050 °C, randomly distributed micrometer-sized compositional irregularities were observed as La-rich regions that were in most cases enriched also with Ti and deficient in Pb and Zr compared to the matrix. Such compositional imperfections were not observed in the PLZT layer fired for the same duration at 1150 °C. The level of microheterogeneity for all elements in the specimen fired at 1150 °C and for Pb, Ti, and Zr in the specimen fired at 1050 °C was below 1% relative at confidence level of 99% while for La it was as much as 2.5% relative. In point-beam line profiles across the active layer starting from the Pt electrode toward the outer surface of the cross-section of the PLZT film, the Pb concentration decreased continuously in both samples, confirming the importance of providing a properly equilibrated partial pressure of Pb around the sample during the entire firing process. Better dielectric and ferroelectric characteristics of the specimen fired at 1150 °C compared to the sample fired at 1050 °C were attributed to the differences in compositional heterogeneity between these samples. The study of the micro-compositional characteristics of these ceramic materials with quantitative WDS mapping has contributed to the optimization of processing parameters and hence to the understanding of the properties of ferroelectric PLZT materials.

Exoskeletal cuticle differentiation during intramarsupial development of Porcellio scaber (Crustacea: Isopoda)

Exoskeletal crustacean cuticle is a calcified apical extracellular matrix of epidermal cells, illustrating the chitin-based organic scaffold for biomineralization. Studies of cuticle formation during molting reveal significant dynamics and complexity of the assembly processes, while cuticle formation during embryogenesis is poorly investigated. This study reveals in the terrestrial isopod Porcellio scaber, the ultrastructural organization of the differentiating precuticular matrices and exoskeletal cuticles during embryonic and larval intramarsupial development. The composition of the epidermal matrices was obtained by WGA lectin labelling and EDXS analysis. At least two precuticular matrices, consisting of loosely arranged material with overlying electron dense lamina, are secreted by the epidermis in the mid-stage embryo. The prehatching embryo is the earliest developmental stage with a cuticular matrix consisting of an epicuticle and a procuticle, displaying WGA binding and forming cuticular scales. In newly hatched marsupial larva manca, a new cuticle is formed and calcium sequestration in the cuticle is evident. Progression of larval development leads to the cuticle thickening, structural differentiation of cuticular layers and prominent cuticle calcification. Morphological characteristics of exoskeleton renewal in marsupial manca are described. Elaborated cuticle in marsupial larvae indicates the importance of the exoskeleton in protection and support of the larval body in the marsupium and during the release of larvae in the external environment.

A novel method for preparation of a platinum catalyst at low temperatures

Uniformly distributed Pt nano-particles with excellent adhesion were deposited on conductive substrates by coating the substrate with a Pt complex precursor and its subsequent reduction with a gaseous reducing agent at temperatures as low as 100 °C. This novel two-step method enables excellent control over the particle size and distribution since it is dependent only upon the deposition of the precursor solution, and there is little to no agglomeration or movement of Pt nano-particles during the reduction process. The good adhesion was the result of the reaction at the solid–gas interface, where the solid precursor was chemically converted to metallic Pt. XPS confirmed that 100% of Pt was in the metallic state. The electrochemical catalytic properties of the Pt nano-particles were tested using cyclic voltammetry in an iodide electrolyte. The prepared samples were also used to assemble dye-sensitised solar cells that achieved a light to electricity conversion efficiency of 5.1% under AM 1.5 illumination.