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

Determination of Cointegrating Rank in Fractional Systems

This paper develops methods of investigating the existence and extent of cointegration in fractionally integrated systems. We focus on stationary series, with some discussion of extension to nonstationarity. The setting is semiparametric, so that modelling is effectively confined to a neighbourhood of frequency zero. We first discuss the definition of fractional cointegration. The initial step of cointegration analysis entails partitioning the vector series into subsets with identical differencing parameters, by means of a sequence of hypopthesis tests. We then estimate cointegrating rank by analysing each subset individually. Two approaches are considered here, both of which are based on the eigenvalues of an estimate of the normalised spectral density matrix at frequency zero. An empirical application to a trivariate series of oil prices is included.Fractional cointegration, long memory.

Finite-size-scaling analysis of the XY universality class between two and three dimensions: An application of Novotny's transfer-matrix method

Based on Novotny's transfer-matrix method, we simulated the (stacked) triangular Ising antiferromagnet embedded in the space with the dimensions variable in the range 2 \le d \le 3. Our aim is to investigate the criticality of the XY universality class for 2 \le d \le 3. For that purpose, we employed an extended version of the finite-size-scaling analysis developed by Novotny, who utilized this scheme to survey the Ising criticality (ferromagnet) for 1 \le d \le 3. Diagonalizing the transfer matrix for the system sizes N up to N=17, we calculated the $d$-dependent correlation-length critical exponent \nu(d). Our simulation result \nu(d) appears to interpolate smoothly the known two limiting cases, namely, the KT and d=3 XY universality classes, and the intermediate behavior bears close resemblance to that of the analytical formula via the 1/N-expansion technique. Methodological details including the modifications specific to the present model are reported

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)

Vibrotactile Stimulus Frequency Optimization for the Haptic BCI Prototype

The paper presents results from a psychophysical study conducted to optimize vibrotactile stimuli delivered to subject finger tips in order to evoke the somatosensory responses to be utilized next in a haptic brain computer interface (hBCI) paradigm. We also present the preliminary EEG evoked responses for the chosen stimulating frequency. The obtained results confirm our hypothesis that the hBCI paradigm concept is valid and it will allow for rapid stimuli presentation in order to improve information-transfer-rate (ITR) of the BCI.Comment: The 6th International Conference on Soft Computing and Intelligent Systems and The 13th International Symposium on Advanced Intelligent Systems, 201

Transfer-matrix approach to the three-dimensional bond percolation: An application of Novotny's formalism

A transfer-matrix simulation scheme for the three-dimensional (d=3) bond percolation is presented. Our scheme is based on Novotny's transfer-matrix formalism, which enables us to consider arbitrary (integral) number of sites N constituting a unit of the transfer-matrix slice even for d=3. Such an arbitrariness allows us to perform systematic finite-size-scaling analysis of the criticality at the percolation threshold. Diagonalizing the transfer matrix for N =4,5,...,10, we obtain an estimate for the correlation-length critical exponent nu = 0.81(5)

Bound-state energy of the d=3 Ising model in the broken-symmetry phase: Suppressed finite-size corrections

The low-lying spectrum of the three-dimensional Ising model is investigated numerically; we made use of an equivalence between the excitation gap and the reciprocal correlation length. In the broken-symmetry phase, the magnetic excitations are attractive, forming a bound state with an excitation gap m_2(<2m_1) (m_1: elementary excitation gap). It is expected that the ratio m_2/m_1 is a universal constant in the vicinity of the critical point. In order to estimate m_2/m_1, we perform the numerical diagonalization for finite clusters with N \le 15 spins. In order to reduce the finite-size errors, we incorporated the extended (next-nearest-neighbor and four-spin) interactions. As a result, we estimate the mass-gap ratio as m_2/m_1=1.84(3)