Alexey V. Umrikhin

Photogeneration of free charge carriers in the donor–acceptor complex TBPDA·(C60)2

The effect of a weak magnetic field with B0 < 10000 G on the photoconductivity of the layered donor–acceptor complex TBPDA·(C60)2 has been studied. The Reaction Yield Detected Magnetic Resonance (RYDMR) spectrum provides evidence of a spin nature of the mechanism of free charge carrier generation in magnetic fields. A model of triplet–triplet annihilation of charge transfer excitons has been suggested. The model interprets the effect of a weak magnetic field on photoconductivity in TBPDA·(C60)2. The photoconductivity spectrum of the complex shows two peaks at 470 and 700 nm. The comparison of this spectrum with the optical absorption one indicates that both intermolecular charge transfer between neighboring C60 molecules and direct charge transfer from the TBPDA to the C60 molecules contribute to free charge carrier generation in TBPDA·(C60)2.

Theoretical description of zirconia ceramics aging kinetics

An analytical approach for fraction calculation of monoclinic phase on zirconia surface under aging conditions was developed. The approach is based on a model of nucleation and growth of areas which underwent tetragonal to monoclinic transformation. Nucleation in this model takes place only at the material surface with nucleation rate proportional to the area of non-transformed zone. The nuclei are conical in shape; their initial dimensions and growth rate are constant. The resulting equations describe factual and observed monoclinic phase content on the surface of zirconia ceramics. The equations correlate well with experimental data on tetragonal zirconia ceramics aging kinetics.

New nanostructured ceramics from baddeleyite with improved mechanical properties for biomedical applications

A method for the preparation of novel nanostructured zirconia ceramics from natural zirconia mineral—baddeleyite—using CaO as the stabilizer is described in the present work. Optimal synthesis conditions, including calcia content, planetary mill treatment regime, sintering time and temperature, corresponding to the highest values of hardness H, Young modulus E, and fracture toughness KC are found. The values of the mechanical properties H = 10.8 GPa, E = 200 GPa, and KC = 13.3 MPa m1/2 are comparable with or exceed the corresponding properties of commercial yttria-stabilized ceramics prepared from chemically precipitated zirconia.

Novel Baddeleyite-Based Zirconia Ceramics for Biomedical Applications

For the first time nanostructured engineering ceramics were prepared from natural zirconia mineral (baddeleyite) with CaO as a tetragonal phase stabilizer. The effect of synthesis conditions on microstructure and mechanical properties of the baddeleyite-based ceramics is reported, furthermore, the effect of calcia content on hardness and fracture toughness is studied. Optimal calcia concentration and synthesis conditions are found, corresponding hardness and fracture toughness values are 10,8 GPa and 13,3 MPa×m1/2. The reported mechanical properties are comparable to those typically reported for yttria-stabilized engineering zirconia ceramics, prepared from chemically synthesized zirconia.

Influence of Static and Microwave Magnetic Fields on Photogeneration of Free Charge Carriers in Donor-Acceptor Complex TBPDA·(C60)2

The effect of a weak magnetic field with B0<1 T on photoconductivity of the donor-acceptor complex TBPDA·(C60)2 has been found. The RYDMR spectrum is evidence of a spin nature of the mechanism of free charge carrier generation in magnetic fields. A model of triplet-triplet annihilation of charge transfer excitons has been suggested. The model interprets the effect of a weak magnetic field on photoconductivity in TBPDA·(C60)2.