Eugene Ryshkewitch

Bio: Eugene Ryshkewitch is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 99 citations.

Transformation Toughening in Zirconia‐Containing Ceramics

Abstract: The recognition of the potential for enhanced fracture toughness that can be derived from controlled, stress-activated tetragonal (t) to monoclinic (m) transformation in ZrO2-based ceramics ushered in a new era in the development of the mechanical properties of engineering ceramics and provided a major impetus for broader-ranging research into the toughening mechanisms available to enhance the fracture properties of brittle-matrix materials. ZrO2-based systems have remained a major focal point for research as developments in understanding of the crystallography of the t→m transformation have led to more-complete descriptions of the origins of transformation toughening and definition of the features required of a transformation-toughening system. In parallel, there have been significant advances in the design and control of microstructure required to optimize mechanical properties in materials developed commercially. This review concentrates on the science of the t→m transformation in ZrO2 and its application in the modeling of transformation-toughening behavior, while also summarizing the microstructural control needed to use the benefits in ZrO2-toughened ceramics.

Vacancy and interstitial defects in hafnia

Abstract: We have performed plane wave density functional theory calculations of atomic and molecular interstitial defects and oxygen vacancies in monoclinic hafnia $({\mathrm{HfO}}_{2})$ The atomic structures of singly and doubly positively charged oxygen vacancies, and singly and doubly negatively charged interstitial oxygen atoms and molecules are investigated We also consider hafnium vacancies, substitutional zirconium, and an oxygen vacancy paired with substitutional zirconium in hafnia Our results predict that atomic oxygen incorporation is energetically favored over molecular incorporation, and that charged defect species are more stable than neutral species when electrons are available from the hafnia conduction band The calculated positions of defect levels with respect to the bottom of the silicon conduction band demonstrate that interstitial oxygen atoms and molecules and positively charged oxygen vacancies can trap electrons from silicon

Structure and electrical levels of point defects in monoclinic zirconia

Abstract: We performed plane wave density functional theory (DFT) calculations of formation energies, relaxed structures, and electrical levels of oxygen vacancies and interstitial oxygen atoms in monoclinic zirconia. The atomic structures of positively and negatively charged vacancies and interstitial oxygen atoms are also investigated. The ionization energies and electron affinities of interstitial oxygen atoms and oxygen vacancies in different charge states are calculated with respect to the bottom of the zirconia conduction band. Using the experimental band offset values at the interface of ${\mathrm{ZrO}}_{2}$ films grown on silicon, we have found the positions of defect levels with respect to the bottom of silicon conduction band. The results demonstrate that interstitial oxygen atoms and positively charged oxygen vacancies can trap electrons from the bottom of the zirconia conduction band and from silicon. Neutral oxygen vacancy serves as a shallow hole trap for electrons injected from the silicon valence band. The calculations predict negative U for the ${\mathrm{O}}^{\ensuremath{-}}$ center and stability of ${\mathrm{V}}^{+}$ centers with respect to disproportionation into ${\mathrm{V}}^{2+}$ and ${\mathrm{V}}^{0}$ in monoclinic zirconia.

Mechanical and physical properties of engineering alumina ceramics

Abstract: The mechanical and physical properties of engineering alumina ceramics (≥ 80% Al2O3) have been reviewed from literature data for the purpose of characterising the thermomechanical response of alumina to non-sintering manufacturing processes in engineering applications involving thermal cycles. Analytical expressions are given for temperature dependence where significant for the purpose of the work.

Ion implantation and thermal annealing of α‐Al2O3 single crystals

Abstract: The effects of ion implantation and post‐implantation thermal annealing of α‐Al2O3 have been characterized using ion scattering‐channeling techniques, and correlated with electron paramagnetic resonance (EPR) and microhardness measurements. Although most of the work was done on 52Cr implanted specimens, preliminary results have been obtained also for implanted 90Zr and 48Ti. For Cr implantation, the Al2O3 lattice damage saturates at relatively low doses, but the near‐surface region never becomes amorphous. A preferential annealing behavior begins in the Al sublattice after ∼800 °C annealing, and in the oxygen sublattice, only after 1000 °C annealing. Lattice location measurements show that after annealing to 1500 °C, Cr is greater than 95% substitutional in the Al sublattice. Above 1500 °C, implanted Cr atoms redistribute by substitutional diffusion processes. EPR measurements show that part, if not all, of the implanted Cr is trivalent and substitutional after annealing to 1600 °C. Microhardness measurem...