Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Optical detection of electron paramagnetic resonance for intrinsic defects produced in ZnO by 2.5-MeV electron irradiation in situ at 4.2 K

Abstract: Intrinsic defects produced in ZnO by 2.5-MeV electron irradiation in situ at 4.2 K are studied by optical detection of electron paramagnetic resonance (ODEPR). Observed in the photoluminescence (PL) are ODEPR signals, which are identified with the oxygen vacancy, ${\mathrm{V}}_{\mathrm{O}}^{+}$, interstitial zinc, ${\mathrm{Zn}}_{i}^{+}$, and zinc-vacancy--zinc-interstitial Frenkel pairs. The Frenkel pairs are primarily observed in their $S=1$ exchange-coupled state, supplying strong evidence that interstitial zinc is a shallow effective mass double donor in ZnO. Annealing stages at $\ensuremath{\sim}65\text{--}119\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $\ensuremath{\sim}145\text{--}170\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are observed for the defects associated with the zinc sublattice and are identified with the migration of interstitial zinc. Although interstitial oxygen is not observed in the ODEPR, a higher-temperature annealing stage observed in the PL at $\ensuremath{\sim}160\text{--}230\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is tentatively identified with the onset of its migration. The oxygen vacancy is stable to $\ensuremath{\sim}400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The relationship between the spin-dependent processes producing the ODEPR signals and the PL of the material remains unclear.

Unique Opportunities for Microstructural Engineering with Duplex and Laminar Ceramic Composites

Abstract: Duplex (two-phase) microstructures and laminar composites offer some unique opportunities for improving the room-temperature mechanical reliability (e.g., flaw tolerance) and the high-temperature microstructural stability (e.g., resistance to grain growth and creep damage) of structural ceramic materials. Examples illustrating the approach to designing novel multiphase microstructures and laminar composites with enhanced structural reliability are given. These are based on current work on various alumina-based ceramics as well as zirconia-, silicon nitride-, and silicon carbide-containing ceramics. Critical issues and areas for future work are discussed.

Catalysis Science of Bulk Mixed Oxides

Abstract: Bulk mixed oxide catalysts are widely used for various applications (selective oxidation catalysts, electrocatalysts for solid oxide fuel cells, and solid oxide electrolyzers for the production of hydrogen), but fundamental understanding of their structure–performance relationships have lagged in the literature. The absence of suitable surface composition and surface structural characterization techniques and methods to determine the number of catalytic active sites, with the latter needed for determination of specific reaction rates (e.g., turnover frequency (1/s)), have hampered the development of sound fundamental concepts in this area of heterogeneous catalysis. This Perspective reviews the traditional concepts that have been employed to explain catalysis by bulk mixed oxides (molybdates, vanadates, spinels, perovskites, and several other specific mixed oxide systems) and introduces a modern perspective to the fundamental surface structure–activity/selectivity relationships for bulk mixed oxide cataly...

On optimum MIMO with antenna selection

Abstract: Wireless communication systems with transmit and receive antenna arrays are studied when antenna selection is used. A case with very limited feedback of information from the receiver to the transmitter is considered, where the only information fed back is the selected subset of transmit antennas to be employed. It is shown that the optimum signaling, for largest ergodic capacity with antenna selection, is generally different from that which is optimum without antenna selection for some range of signal-to-noise ratios.