24 research outputs found
Heat capacity, Raman, and Brillouin scattering studies of M2O–MgO–WO3–P2O5 glasses (M=K,Rb)
The authors report the results of temperature-dependent Brillouin scattering from both transverse and longitudinal acoustic waves, heat capacity studies as well as room temperature Raman scattering studies on M2O–MgO–WO3–P2O5 glasses (M=K,Rb). These results were used to obtain information about structure and various properties of the studied glasses such as fragility, elastic moduli, ratio of photoelastic constants, and elastic anharmonicity. They have found that both glasses have similar properties but replacement of K+ ions by Rb+ ions in the glass network leads to decrease of elastic parameters and P44 photoelastic constant due to increase of fragility. Based on Brillouin spectroscopy they show that a linear correlation between longitudinal and shear elastic moduli holds over a large temperature range. This result supports the literature data that the Cauchy-type relation represents a general rule for amorphous solids. An analysis of the Boson peak revealed that the form of the frequency distribution of the excess density of states is in agreement with the Euclidean random matrix theory. The reason of the observed shift of the maximum frequency of the Boson peak when K+ ions are substituted for Rb+ ions is also briefly discussed
The effect of compressive strain on the Raman modes of the dry and hydrated BaCe0.8Y0.2O3 proton conductor
The BaCe0.8Y0.2O3-{\delta} proton conductor under hydration and under
compressive strain has been analyzed with high pressure Raman spectroscopy and
high pressure x-ray diffraction. The pressure dependent variation of the Ag and
B2g bending modes from the O-Ce-O unit is suppressed when the proton conductor
is hydrated, affecting directly the proton transfer by locally changing the
electron density of the oxygen ions. Compressive strain causes a hardening of
the Ce-O stretching bond. The activation barrier for proton conductivity is
raised, in line with recent findings using high pressure and high temperature
impedance spectroscopy. The increasing Raman frequency of the B1g and B3g modes
thus implies that the phonons become hardened and increase the vibration energy
in the a-c crystal plane upon compressive strain, whereas phonons are relaxed
in the b-axis, and thus reveal softening of the Ag and B2g modes. Lattice
toughening in the a-c crystal plane raises therefore a higher activation
barrier for proton transfer and thus anisotropic conductivity. The experimental
findings of the interaction of protons with the ceramic host lattice under
external strain may provide a general guideline for yet to develop epitaxial
strained proton conducting thin film systems with high proton mobility and low
activation energy
An atomic force microscopy study of diamond dissolution features: The effect of H(2)O and CO(2) in the fluid on diamond morphology
Heat capacity, Raman, and Brillouin scattering studies of M2O–MgO–WO3–P2O5 glasses (M=K,Rb)
Hydrogen bond symmetrization and equation of state of phase D
[1] We have synthesized phase D at 24 GPa and at temperatures of 1250-1100°C in a multianvil press under conditions of high silica activity. The compressibility of this high-silica-activity phase D (Mg 1.0 Si 1.7 H 3.0 O 6 ) has been measured up to 55.8 GPa at ambient temperature by powder X-ray diffraction. The volume (V) decreases smoothly with increasing pressure up to 40 GPa, consistent with the results reported in earlier studies. However, a kink is observed in the trend of V versus pressure above ∼40 GPa, reflecting a change in the compression behavior. The data to 30 GPa fit well to a third-order Birch-Murnaghan equation of state (EoS), yielding V o = 85.1 ± 0.2 Å 3 ; K o = 167.9 ± 8.6 GPa; and K′ o = 4.3 ± 0.5, similar to results for Fe-Al-free phase D reported b