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.

In Situ Spectroscopic Investigation of the Molecular and Electronic Structures of SiO2 Supported Surface Metal Oxides

Abstract: Groups 5−7 transition metal oxides (V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, Re2O7) were anchored on a SiO2 support via incipient wetness impregnation and calcination. The molecular and electronic structures of the dehydrated supported metal oxides and the SiO2 support were determined by combined in situ Raman, IR, and UV−vis spectroscopy under dehydrated conditions. In situ Raman characterization reveals that the supported metal oxides are only present as surface species below the maximum dispersion limit (where crystalline metal oxide nanoparticles are absent). In situ IR analysis shows that the surface metal oxides anchor to the SiO2 support at Si−OH and adjacent Si−O−Si sites. The corresponding in situ UV−vis diffuse reflectance spectroscopy indicates that the dehydrated surface metal oxide species are present as isolated structures. Isotopic D2O−H2O exchange demonstrates that the dehydrated surface MOx species possess the MO oxo functionality but no MOH bonds. The number of MO oxo bonds was found to be r...

Phase diagram of the relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3

Abstract: Recently, a new orthorhombic phase has been discovered in the ferroelectric system $(1\ensuremath{-}x)\mathrm{Pb}({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}x{\mathrm{PbTiO}}_{3}$ $(\mathrm{PZN}\ensuremath{-}x\mathrm{PT})$ for $x=9%,$ and for $x=8%$ after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations $10%l~xl~15%.$ The orthorhombic phase was observed for $x=10%,$ but, surprisingly, for $xg~11%$ only a tetragonal phase was found down to 20 K. The orthorhombic phase thus exists only in a narrow concentration range with near-vertical phase boundaries on both sides. This orthorhombic symmetry ${(M}_{C}$ type) is in contrast to the monoclinic ${M}_{A}$-type symmetry recently identified at low temperatures in the $\mathrm{Pb}({\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}){\mathrm{O}}_{3}$ (PZT) system over a triangle-shaped region of the phase diagram in the range $x=0.46--0.52.$ To further characterize this relaxor-type system, neutron inelastic scattering measurements have also been performed on a crystal of $\mathrm{PZN}\ensuremath{-}x\mathrm{PT}$ with $x=15%.$ The anomalous soft-phonon behavior (``waterfall'' effect) previously observed for $x=0%$ and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.