James E. Maslar

Phase transitions and microwave dielectric properties in the perovskite-like Ca(Al0.5Nb0.5)O3−CaTiO3 system

Phase transitions and microwave dielectric properties in the (1−x)Ca(Al0.5Nb0.5)O3–xCaTiO3 system were analyzed using x-ray and neutron powder diffraction, transmission electron microscopy, Raman spectroscopy, and dielectric measurements at microwave frequencies (2–8 GHz). Rietveld structural refinements demonstrated that both end compounds exhibit similar octahedral tilted frameworks, while in Ca(Al0.5Nb0.5)O3, tilting is superimposed onto NaCl-type ordering of Al and Nb on the B sites. Accordingly, the room-temperature structures of CaTiO3 and Ca(Al0.5Nb0.5)O3 are described by orthorhombic Pbnm and monoclinic P21/n symmetries, respectively, with similar lattice parameters, √2ac×√2ac×2ac (where ac is the lattice parameter of cubic perovskite). The (1−x)Ca(Al0.5Nb0.5)O3–xCaTiO3 system features both cation ordering and octahedral tilting phase transitions. The Ca(Al0.5Nb0.5)O3 structure remains ordered at least up to 1625 °C. However, the temperature of the order/disorder transition decreases rapidly with ...

In Situ Raman Spectroscopic Investigation of Aqueous Iron Corrosion at Elevated Temperatures and Pressures

In situ Raman spectroscopy was employed to investigate iron corrosion in air saturated water at a pressure of 25.1 MPa and temperatures from 21 to 537°C. Upon heating, various combinations of Fe 3 O 4 . α-Fe 2 O 3 , γ-FeOOH, and γ-Fe 2 O 3 were observed depending on the location on or temperature of the iron coupon. In some cases, different species were observed at the same temperature at different locations on the surface. This was attributed to oxygen concentration gradients in the solution caused by recirculation zones in the cell. The surface of the corrosion coupon changed little after it was heated to 537°C. This was attributed to the formation of a relatively thick, protective oxide scale after exposure to supercritical water. The ex situ Raman spectra were very similar to the in situ spectra obtained during cooling but different from those obtained during heating. This indicates that the corrosion layer present during cooling is similar to that observed ex situ but different from that observed during heating. Ex situ characterization of the coupon identified a two layered structure: an inner corrosion layer consisting of Fe 3 O 4 and α-Fe 2 O 3 and an outer layer consisting of γ-Fe 2 O 3 and α-Fe 2 O 3 .

First-order Raman spectra ofAB1∕2′B1∕2″O3double perovskites

First principles computations of Raman intensities were performed for perovskite-family compound CaAl

In Situ Raman Spectroscopic Investigation of Stainless Steel Hydrothermal Corrosion

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In situ Raman spectroscopic investigation of zirconium-niobium alloy corrosion under hydrothermal conditions

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Effects of 1:1 B-cation order on Raman scattering in complex perovskites AB′B″0.5O30.5

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In Situ Raman Spectroscopic Investigation of Nickel Hydrothermal Corrosion

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An Investigation of Particle Dynamics in a Rotating Disk Chemical Vapor Deposition Reactor

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Alloy 600 Aqueous Corrosion at Elevated Temperatures and Pressures: An In Situ Raman Spectroscopic Investigation

(CAN). This compound features 1:1 (NaCl-type) ordering of Al and Nb superimposed onto the

In Situ Gas Phase Diagnostics for Hafnium Oxide Atomic Layer Deposition

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