17,197 research outputs found
Defect chemistry of yttrium-doped barium zirconate: a thermodynamic analysis of water uptake
Thermogravimetry has been used to evaluate the equilibrium constants of the water incorporation reaction in yttrium-doped BaZrO3 with 20-40% yttrium in the temperature range 50-1000 °C under a water partial pressure of 0.023 atm. The constants, calculated under the assumption of a negligible hole concentration, were found to be linear in the Arrhenius representation only at low temperatures (≤500 °C). Nonlinearity at high temperatures is attributed to the occurrence of electronic defects. The hydration enthalpies determined here range from -22 to -26 kJ mol^-1 and are substantially smaller in magnitude than those reported previously. The difference is a direct result of the different temperature ranges employed, where previous studies have utilized higher temperature thermogravimetric measurements, despite the inapplicability of the assumption of a negligible hole concentration. The hydration entropies measured in this work, around -40 J K^-1 mol^-1, are similarly smaller in magnitude than those previously reported and are considerably smaller than what would be expected from the complete loss of entropy of vapor-phase H2O upon dissolution. This result suggests that substantial entropy is introduced into the oxide as a consequence of the hydration. The hydration reaction constants are largely independent of
yttrium concentration, in agreement with earlier reports
Double Resonance in Dalitz Plot of M(pLambda)-M(KLambda) in DISTO Data on p+p rightarrow p+Lambda+K+ at 2.85 GeV
The X(2265) resonance was previously observed in DISTO data of p+p rightarrow
p+Lambda+K+ at 2.85 GeV on an attempt of searching for the kaonic nuclear state
K-pp rightarrow p + Lambda. In the present paper we report an additional
finding, namely, a double resonance type phenomena, not only with a peak at
M(pLambda) = 2265 MeV/c2 but also a broad bump at M(K+ Lambda) ~ 1700 MeV/c2.
This "double-resonance" zone is expressed as XY(2265, 1700). The latter bump
may result from nearby nucleon resonances, typically N*(1710), as well as by
attractive K - Lambda final-state interaction. We point out that this double
resonance XY(2265, 1700) as seen in DISTO at 2.85 GeV cannot be populated
kinematically in a HADES experiment at 3.5 GeV.Comment: 4 pages, 3 figures, HYP2015 conferenc
High Total Proton Conductivity in Large-Grained Yttrium-Doped Barium Zirconate
Barium zirconate has attracted particular attention among candidate proton conducting electrolyte materials for fuel cells and other electrochemical applications because of its chemical stability, mechanical robustness, and high bulk proton conductivity. Development of electrochemical devices based on this material, however, has been hampered by the high resistance of grain boundaries, and, due to limited grain growth during sintering, the high number density of such boundaries. Here, we demonstrate a fabrication protocol based on the sol−gel synthesis of nanocrystalline precursor materials and reactive sintering that results in large-grained, polycrystalline BaZr_(0.8)Y_(0.2O3−δ) of total high conductivity, 1 × 10^(−2) Scm^(−1) at 450 °C. The detrimental role of grain boundaries in these materials is confirmed via a comparison of the conductivities of polycrystalline samples with different grain sizes. Specifically, two samples with grain sizes differing by a factor of 2.3 display essentially identical grain interior conductivities, whereas the total grain boundary conductivities differ by a factor of 2.5−3.2, depending on the temperature (with the larger-grained material displaying higher conductivity)
The relation between post-shock temperature, cosmic-ray pressure and cosmic-ray escape for non-relativistic shocks
Supernova remnants are thought to be the dominant source of Galactic cosmic
rays. This requires that at least 5% of the available energy is transferred to
cosmic rays, implying a high cosmic-ray pressure downstream of supernova
remnant shocks. Recently, it has been shown that the downstream temperature in
some remnants is low compared to the measured shock velocities, implying that
additional pressure support by accelerated particles is present.
Here we use a two-fluid thermodynamic approach to derive the relation between
post-shock fractional cosmic-ray pressure and post-shock temperature, assuming
no additional heating beyond adiabatic heating in the shock precursor and with
all non-adiabatic heating occurring at the subshock. The derived relations show
that a high fractional cosmic-ray pressure is only possible, if a substantial
fraction of the incoming energy flux escapes from the system. Recently a shock
velocity and a downstream proton temperature were measured for a shock in the
supernova remnant RCW 86. We apply the two-fluid solutions to these
measurements and find that the the downstream fractional cosmic-ray pressure is
at least 50% with a cosmic-ray energy flux escape of at least 20%. In general,
in order to have 5% of the supernova energy go into accelerating cosmic rays,
on average the post-shock cosmic-ray pressure needs to be 30% for an effective
cosmic-ray adiabatic index of 4/3.Comment: 9 pages, 6 color figures. This is updated with a corrected figure 5a
and 5b, reflecting an ApJ erratu
Anisotropic magnetic diffuse scattering in an easy-plane type antiferromagnet ErNiGe
We report on neutron scattering studies of a rare earth intermetallic
compound ErNiGe. Polarized neutron scattering experiments revealed
that the magnetic ordered moment lies in ab-plane. Taking account of
a lack of the third higher harmonic reflection, ErNiGe is
considered to have a helical magnetic structure. The magnetic scattering
profiles along the - and the -directions are well
described by the sum of Gaussian and modified-Lorentzian terms, even far below
, indicating that short-range orders coexist with a
long-range order. Interestingly, the modified-Lorentzian-type diffuse
scattering is not present in the profiles along the -direction.
The anisotropy of the diffuse scattering suggests that the short-range-order
consists of one dimensional long-range helices along the c-axis.Comment: 4 pages, to be published in J. Phys.: Condens. Matter (HFM2008
Phase Field Model for Dynamics of Sweeping Interface
Motivated by the drying pattern experiment by Yamazaki and Mizuguchi[J. Phys.
Soc. Jpn. {\bf 69} (2000) 2387], we propose the dynamics of sweeping interface,
in which material distributed over a region is swept by a moving interface. A
model based on a phase field is constructed and results of numerical
simulations are presented for one and two dimensions. Relevance of the present
model to the drying experiment is discussed.Comment: 4 pages, 7 figure
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