Alexander Reinholdt

Protonic conductivity of nano-structured yttria-stabilized zirconia: dependence on grain size

The conductivity of dense ceramics of nanocrystalline yttria-stabilized zirconia (nano-YSZ), with average grain sizes ranging from 13 nm to 100 nm, was measured in wet and dry air as a function of temperature between 30 °C and 500 °C. Under wet conditions (pH2O = 2.3 × 10−2 atm) the measured conductivity at low temperatures (<150 °C) was found to increase strongly with decreasing grain size, displaying a highly non-linear dependence on grain size. This is interpreted as evidence of the protonic conductivity of grain boundaries increasing with decreasing grain size.

Novel laser universal cluster ablation source—LUCAS

The construction and operation of new laser-based universal evaporation/ablation source of high cluster yield combined with an ultra high vacuum experiment chamber for in situ investigations is described. The source was designed for cluster beam production. The beam is characterized by uniform cluster motion and low collision rates that leads to quite narrow distribution of deposited clusters. This source is applied especially for high refractory materials or/and for materials with high melting temperatures. Some examples of the synthesis of yttrium nanoclusters and chemical solid state reaction of these clusters with oxygen and hydrogen are presented.

Synthesis of Nanostructured Yttrium with the Use of Cluster Beams and Investigation of the Optical and Electrical Properties of Yttrium Hydride Species

The preparation of new types of nanosystems based on metallic yttrium nanoparticles, which are difficult to produce by traditional methods due to the high melting temperature and the extremely high oxidizability of this metal, has been investigated. The materials are prepared on an original high-vacuum setup intended for the formation of metal nanoparticle beams by laser ablation. Yttrium nanoparticles are synthesized, and their chemical reactions with hydrogen are studied at room temperature. It is found that the reaction at low hydrogen pressures (∼10−3 Pa) leads to the formation of YH2 dihydride particles with metal properties. An increase in the hydrogen pressure to ∼100 Pa results in the transformation of metal-like YH2 nanoparticles into dielectric YH3 − x (x < 1) nanoparticles. It is revealed that the last reaction corresponding to the metal-dielectric phase transition is reversible with respect to the pressure of the hydrogen atmosphere.

On the high temperature stability of γ-Al2O3/Ti0.33Al0.67N coated WC–Co cutting inserts

Abstract The high temperature stability of γ-Al2O3 films deposited using filtered cathodic arc and plasma assisted chemical vapor deposition on Ti0.33Al0.67N coated WC–Co cutting inserts is investigated. X-ray diffractometry reveals that filtered cathodic arc deposited films transform partially into the thermodynamically stable α-Al2O3 phase at a temperature of 1000°C. The γ to α-Al2O3 transformation for plasma assisted chemical vapor deposition grown films is observed at 900°C. These results are in qualitative agreement with differential scanning calorimetry measurements. Transmission electron microscopy on filtered cathodic arc and plasma assisted chemical vapor deposition films annealed at 900°C reveals the existence of hexagonal AlN in the Ti0.33Al0.67N interlayer, as well as Al depletion at the Al2O3/Ti0.33Al0.67N interface. After annealing the plasma assisted chemical vapor deposition sample at 900°C, α-Al2O3 grains with a size of ∼100 nm are observed inside the γ-Al2O3 matrix, while for filtered cathodic arc samples only the γ-phase is identified. Transmission electron microscopy analysis on both filtered cathodic arc and plasma assisted chemical vapor deposition samples annealed at 1000°C shows that the original Al2O3/Ti0.33Al0.67N/WC–Co layer architecture is no longer intact. The formation of TiO2 is detected along the growth direction of the Al2O3 films. The present study suggests that not only the morphology and the impurities incorporated into γ-Al2O3 but also stability of the Ti0.33Al0.67N interlayer determine the high temperature stability of γ-Al2O3/Ti0.33Al0.67N coated hardmetal.

New Laser Ablation Cluster Source for a Synthesis of Magnetic Nanoparticles, and FMR Study of Ni:MgF2 Composites

A new technique for synthesis of Ni magnetic nanoparticles in diamagnetic matrix by using a novel laser universal cluster ablation source (LUCAS) is presented. The source has been developed specially for highly refractory materials with high melting temperatures. Ablation/evaporation laser pulses were applied to the Ni bulk target to form metal vapor in high pressure seeding Ar-gas, and then expansion of the material vapor through a nozzle with the carrier Ar gas was performed. The nickel nanoparticles deposited on a substrate surface were protected by a complementary electron sputtering of magnesium fluoride bulk material. Electron microscopy showed that a highly homogeneous dispersion of the crystalline Ni nanoparticles with a size of near 3 nm was formed in the deposited layer. The magnetic properties of the nanostructured Ni:MgF2 composite were investigated by magnetic resonance technique in X-band (9.8 GHz) at room temperature. A highly anisotropic ferromagnetic resonance (FMR) responce of the Ni:MgF2 composite was found. Broadening of the FMR signal, when the DC magnetic field is rotated towards the plane of the composite, was also observed. Effective media approach to the FMR in thin granular magnetic films was applied to analyze the resonance field and linewidth dependencies on orientation, and the value of the magnetization of the synthesized Ni:MgF2 composite was extracted.