${\mathrm{Cu}}_{2}\mathrm{Se}$ and ${\mathrm{Cu}}_{2}\mathrm{S}$ are excellent model systems of superionic conductors with large diffusion coefficients that have been reported to exhibit different solidlike and liquidlike Cu-ion diffusion. In this paper, we clarify the atomic dynamics of these compounds with temperature-dependent ab initio molecular dynamics (AIMD) simulations and inelastic neutron scattering experiments. Using the dynamical structure factor and Van Hove correlation function, we interrogate the jump time, hopping length distribution, and associated diffusion coefficients. In cubic ${\mathrm{Cu}}_{2}\mathrm{Se}$ at 500 K, we find solidlike diffusion with Cu jump lengths matching well the first-neighbor Cu-Cu distance of \ensuremath{\sim}3 \AA{} in the crystal, and clearly defined optic phonons involving Cu vibrations. Above 700 K, the jump-length distribution becomes a broad maximum centered around 4 \AA{}, spanning the first and second neighbor lattice distances, and a concurrent broadening of the Cu-phonon density of states. Further, above 900 K, the Cu diffusion becomes close to liquidlike, with distributions of Cu atoms continuously connecting crystal sites, while the vibrational modes involving Cu motions are highly damped, though still not fully overdamped as in a liquid. At low temperatures, the solidlike diffusion is consistent with previous x-ray diffraction and quasielastic neutron scattering experiments, while the higher-temperature observation of the liquidlike diffusion is in agreement with previous AIMD simulations. We also report AIMD simulations in ${\mathrm{Cu}}_{2}\mathrm{S}$ in the hexagonal and cubic superionic phases, and observe nearly liquidlike diffusion above \ensuremath{\sim}500 K. The calculated ionic conductivity is in fair agreement with reported experimental values.

Abstract Determination of impurities in graphite is very important for its quality control, as their presence even at trace level can affect the performance of graphite in various applications. Graphite with equivalent boron content (EBC) less than 5 mg kg-1 is considered as nuclear grade. Elements with high neutron absorption cross section (boron and rare earths) contribute significantly to EBC. Non-destructive method is preferred as there is no sample processing and probability of loss of volatile elements while digestion. Proton Induced Gamma Ray Emission (PIGE), Instrumental Neutron Activation Analysis (INAA) were utilized for the non-destructive determination of impurities in both nuclear and commercial grade graphite. Low Z elements like Li, B, F, Na, Al and Si were detected in graphite by PIGE whereas Na, K, Sc, Cr, Mn, Fe, Co, Zn, Rb, Zr, Sb, Cs, La, Ce, Nd, Sm, Eu, Tb, Yb, Hf, Ta, Th were determined using INAA. Few elements like Ca, Ti, V, Ni, Sr and Pb remained undetected by both the non-destructive techniques. These elements were determined by Total Reflection X-ray Fluorescence (TXRF) after digestion of the graphite samples by dry ashing. Combinations of these techniques were utilized to get maximum information regarding the impurities present in graphite. GRAPHICAL ABSTRACT

Lanthanum tellurites, La2Te3O9 and La2Te4O11, have been prepared by the solid state synthesis route and characterized for their phase and chemical compositions by XRD and ICP-AES analyses. The molar enthalpies of solution of La2Te3O9(s), La2Te4O11(s), La2O3(s) and TeO2(s) in 0.150 dm3 of 10.98 mol dm−3 HCl were measured using an isoperibol calorimeter. From these results and other auxiliary data the standard molar enthalpy of formation of La2Te3O9(s) and La2Te4O11(s) were derived to be (−2814.6 ± 12.9) kJ mol−1 and (−3116.5 ± 17.3) kJ mol−1, respectively, at 298.15 K which are the first reported thermodynamic data on these compounds at 298.15 K.

The vaporization behavior of the intermetallic compound RuTe2(s) was studied in the temperature range of 831–1148 K by the Knudsen effusion technique. As a prerequisite to the study, the nature of the vaporization equilibrium was first obtained. Phase analysis of the partially evaporated sample of RuTe2(s) from thermogravimetric experiment carried out in inert environment showed the TG residue to be a biphasic mixture of Ru(s) and RuTe2(s). This result together with the available thermodynamic information of Te vapor revealed that the compound incongruently volatilize as RuTe2(s)=Ru(s)+Te2(g). The equilibrium vapor pressure of Te2(g) derived from the measurement at the different temperatures could be expressed as ln(p/Pa)(±0.33)=−33231.2/T+33.67 (831≤T/K≤1148). The result of this study is discussed in the light of the reported data on the intermetallic compound.

The thermodynamic stability of rubidium thorate, Rb2ThO3(s), was determined from vaporization studies using the Knudsen effusion forward collection technique. Rb2ThO3(s) vaporized incongruently and predominantly as Rb2ThO3(s)=ThO2(s)+2Rb(g)+1/2O2(g). The equilibrium constant K=pRb2·pO21/2 was evaluated from the measurement of the effusive flux due to Rb vapor species under the oxygen potential governed by the stoichiometric loss of the chemical component Rb2O from the thorate phase. The Gibbs energy of formation of Rb2ThO3 derived from the measurement and other auxiliary data could be given by the equation, ΔfG°(Rb2ThO3,s)=−1794.7+0.42T±5.0kJmol−1(1058⩽T/K⩽1187).

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Thermodynamic stability of cesium zirconate was determined by measuring the vapour pressure of Cs2O using Knudsen effusion forward collection technique. Cs2ZrO3(s) vaporized incongruently according to the reactionCs2ZrO3(s)=ZrO2(s)+Cs2O(g)The Gibbs energy of formation of Cs2ZrO3 obtained from the vapour pressure of Cs2O and other auxiliary data could be given by the equationΔfG° (Cs2ZrO3, s) (±18.0 kJ/mol)=−1671.6+0.440T(1142≤T/K≤1273)