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High-Temperature Phase Transitions In Rbh2po4, Heber Jair Martinez
High-Temperature Phase Transitions In Rbh2po4, Heber Jair Martinez
Open Access Theses & Dissertations
Recent studies have shown that the proton conductivity of MH2PO4 (M=Cs, Rb) solid-acids exhibits a sharp, several-order-of-magnitude increase upon heating above a certain temperature threshold [Boysen et al., Chem. Mater. 15, 727(2003), Boysen et al., Chem. Mater. 16, 693(2004)]. This so-called superprotonic behavior allows the above-mentioned compounds to function as fuel-cell electrolytes at intermediate temperatures [Boysen et al., Science 303, 68(2004)], a remarkable application that has attracted much interest. Yet, the crystal structures and microscopic mechanisms responsible for this heating-induced proton conductivity enhancement are not fully understood.
Our group has previously demonstrated [Botez et al., J. Chem. Phys. 127, 194701(2007)] …
Pressure Induced Phase Transformation Of Sno2: An Ab Initio Constant Pressure Study, Daniel Tesfai Yehdego
Pressure Induced Phase Transformation Of Sno2: An Ab Initio Constant Pressure Study, Daniel Tesfai Yehdego
Open Access Theses & Dissertations
The behavior of SnO2 under rapid hydrostatic pressures is studied using constant-pressure ab initio simulations. The rutile-type SnO2 gradually transforms into the CaCl2-type structure at 15 GPa. At a pressure of about 20 GPa, a phase transformation into a cubic fluorite-type structure is observed. The orthorhombic Pnma cotunnite-structured phase is observed above 150 GPa. The mechanisms of these phase transformations at the atomistic level are discussed.
Observed Superspin-Glass Behavior In Ni0.5zn0.5fe2o4 Nanoparticles, Antony Adair
Observed Superspin-Glass Behavior In Ni0.5zn0.5fe2o4 Nanoparticles, Antony Adair
Open Access Theses & Dissertations
In this investigation we seek to identify the magnetic behavior of Ni0.5Zn0.5Fe2O4 nanoparticles though AC-susceptibility and DC-magnetization measurements. Powder x-ray diffraction was performed to determine the purity and average diameter ( ~ 9nm) of the particles. Aditionally, structure was confirmed by comparison through the International Centre for Diffraction Data's Powder Diffraction File [52] (PDF # 08-0234).
Zero-field cooled and field cooled DC magnetization measurements (bifurcation and blocking temperature), as well as M(H) hysteresis (below and above the blocking temperature) lead us to initially suggest that the material may in fact be superparamagnetic. However, further investigation of the real AC susceptibility …