The formation of a ternary cerium germanide Ce4Rh4Ge3 was established. The crystal structure of this novel compound was determined by mean of single crystal and powder X-ray diffraction techniques to be of the monoclinic Nd4Rh4Ge3-type (space group C2/c, No.15, Pearson symbol mS44, Z = 4) with the lattice parameters: a = 21.027(6) Å, b = 5.7248(16) Å, c = 7.999(3) Å, β = 110.39(3) deg. The low-temperature physical properties of Ce4Rh4Ge3 were studied by means of magnetic susceptibility, magnetization, heat capacity, electrical resistivity and magnetoresistance measurements. The compound was found to order ferromagnetically at TC = 4.2(2) K. Its physical behavior in the paramagnetic state was found to be governed by interplay of crystalline electric field effect and Kondo interactions, with possible contribution due to valence fluctuations associated with one of the two inequivalent cerium atoms located in the crystallographic unit cell of Ce4Rh4Ge3.
The system Y2Co17Cx was investigated by nuclear magnetic resonance zero field spin echo spectroscopy of 89Y. From the satellite line intensity it was deduced that the limiting concentration of the interstitial solution of carbon is very low and corresponds to x = 0.07. The relative insensitivity of the Curie temperature to carbon concentration in this system is in agreement with this behaviour.
Solid solutions of the (UAs)x(ThSe)1 − x system for x ⩾ 0.7 were measured in pulsed magnetic fields up to 40 T at temperatures 4.2 and 77 K. Metamagnetic transitions directly from antiferro- to ferromagnetic order were found in samples with x ⩽ 0.8, these samples being ferromagnetically ordered in magnetic fields above 10T. The intensity of magnetic fields up to 40 T is not sufficient to change antiferromagnetic order into ferromagnetic order for samples in the UAs-rich region with x ⩾ 0.85 and probably only ferrimagnetic ordering is created.
The melt-spinning technique was used to prepare amorphous Hf0.67Co0.33 − xNix alloys with compositions x = 0.00, 0.06, 0.11, 0.165, 0.22, 0.27 and 0.33. The crystallization process of these alloys was monitored by differential scanning calorimetry and X-ray diffraction. The crystallization temperature T1 was 776 K for x = 0.00 and decreased from 787 K to 772 K with increasing x for 0.06 ⩽ ⩽ 0.33. The heat of crystallization ΔH1 was found to decrease with increasing x values. Amorphous Hf0.67Co0.33 − xNix alloys with 0.00 ⩽ x < 0.165 crystallized directly to the thermodynamically stable phase with cubic Ni2Ti-type structure. Amorphous Hf2Ni crystallized to the tetragonal Al2Cu-type structure, while a two-phase region was observed for 0.165 ⩽ x < 0.33. The activation energies for the crystallization processes, evaluated by the Kissinger method, increased almost linearly with x from 286 kJ mol−1 for Hf2Co to 488 kJ mol−1 for Hf2Ni.
The ternary alkaline earth transition metal hydrides Ca2FeH6, Sr2FeH6, Eu2FeH6, Mg2RuH6, Mg2OsH6 and Ca2OsH6 were synthesized from metal mixtures at 450–500°C and 70–130 bar H2 pressure. They crystallize with the f.c.c. K2PtCl6 structure type and contain octahedral [TH6]4− (T = Fe, Ru, Os) hydride complexes with bond distances [T-D] = 1.618(5) Å (Ca1.98Mg0.02FeD6), 1.673(4) Å (Mg2RuD6), 1.682(2) Å (Mg2OsD6) and 1.728(5) Å (Ca1.92Mg0.08OsD6) as refined from neutron powder diffraction of magnesium-containing deuterides. In systems containing two alkaline earth elements quaternary hydrides with primitive cubic structures are formed in which the alkaline earth atoms are ordered. Preliminary neutron data on iron-based CaMgFeD6 and nickel-based CaMgNiD4 confirm the presence of octahedral [FeD6]4− and tetrahedral [NiD4]4− complexes respectively.
The solid state phase transitions in certain organic molecular plastic crystals reversibly absorb large amounts of heat. These have potential applications for use in thermal energy storage. Pure plastic crystals undergo first order transformations but the binaries exhibit complex behavior. A phase diagram for two energetic materials, 2,2-dimethyl-1,3-propanediol (NPG) and 2-amino-2-methyl-1,3-propanediol (AMPL) plastic crystals is proposed. This diagram was determined by high temperature Guinier X-ray diffraction and differential scanning calorimetric methods. It is found that the AMPL rich binaries supercool and the high temperature phase can be triggered by straining the material to release an estimated amount of 50–53 cal g−1 at room temperature. The structure of the high temperature γ′ phase of AMPL is determined as body centered cubic with a lattice parameter 6.778 Å at 92 °C; which is much lower than that of 8.8381 Å at 46.5 °C for the face centered cubic γ phase of NPG. A eutectoid γ → α + β transformation occurs at 20 °C. In the AMPL rich mixtures heat is absorbed in the α + γ and α + γ′ regions over a wide temperature range. An interesting feature is that there are binary equilibria between the γ and γ′ phases, with molecular rotations. Some rather uncommon thermal contractions with abrupt changes of 28% are observed in γ and γ′ phases in heating AMPL-25 mol.% NPG binary mixture.
A method of calculating the elastic contribution to the hydrogen chemical potential and the mean elastic interaction energy for hydrogen atoms dissolved in metals is presented. The method, which is based on the Finite-Element Method (FEM), makes it possible to solve the elastic problem for the metal-hydrogen system in arbitrary geometries and for arbitrary boundary conditions. Two examples are presented: In the first example the method is applied to calculate the mean hydrogen-hydrogen interaction energy in substrate-supported PdHx films. Results from this calculation indicate a decreased strength of the elastic interaction for thin PdHx films as compared to free bulk PdHx, which is in qualitative agreement with recent experiments. In the second example the anomalous “up-hill” diffusion of hydrogen in Pd-Pt alloys is examined. Results here support a previously reported model calculation which has shown that the unusual diffusion behaviour can be explained in terms of non-local elastic interactions between the dissolved hydrogen atoms.
The cycling lives of metal hydride electrodes using mischmetal (Mm)-based alloys were significantly impaired by a stoichiometric deviation to the Mm-deficient side, because elements such as manganese and aluminum were preferentially precipitated at grain boundaries. Heat treatment at 1000 °C was effective for improving the cycling lives.
X-ray powder diffraction data for Hf 2 Fe were collected at room temperature and refined according to the Rietveld profile method. In the space group Fd 3 m , the hafnium atoms occupy 16c and 48f positions and the iron atoms occupy the 32e position. The coordination numbers of the three coordination polyhedra are 16c-12, 48f-14 and 32e-12. These results are the correction of a previously reported structure of prototypic Ti 2 Ni.
The IR absorption spectra of tetragonal copper manganite CuxMn3-x(O4) spinels (O < x < 1) have singled out a discontinuity in cation distribution to occur at x > 0.60 in conformity with that recorded by our previous measurements and have warranted the existence of a more complex cation distribution than that proposed earlier. It has been concluded from this study that the ionic configuration for x < 0.60, i.e. (Cux+-Mn1-x2+)A(Mn2-x3+ Mnx4+)BO4(2)-, changes for x > 0.60 to (Cux-y+Mn1-x+y2+)A(Cuy2+Mn2-x-y3+Mnx4+)(B)O4(2-), where y represents a low value (less than 0.20).When the oxidation of Mn2+ and Cu+ ions is achieved below 450-degrees-C, IR absorption measurements confirm the formation of a cation-deficient metastable spinel phase Cu1.5Mn1.5O4+delta with a 1:3 octahedral superstructure.
The ternary oxides in the YMoO system are of interest from the viewpoint of fission product interactions in the irradiated fuels of fast nuclear reactors. For the thermodynamic characterization of Y 2 MoO 6 the e.m.f. of the galvanic cell Pt, Y 2 MoO 5 , Y 2 MoO 6 ¦15YSZ¦O 2 ( P o 2 = 0.21 atm), Pt (where 15YSZ denotes 15 mass% Y 2 O 3 -stabilized ZrO 2 ) was measured over the range 1015–1222 K, where the e.m.f. data could be represented by the expression E 1 = 1288.59 − 0.52170 T ± 2.71mV Combining this with standard Gibbs energy of formation, ΔG o f , ox , of Y 2 MoO 5 from the constituent binary oxides, ΔG o f , ox of Y 2 MoO 6 was computed to be ΔG o f , ox ( Y 2 MoO 6 ) = − 92.18 − 0.01776 T .
Intermetallic compounds which react with hydrogen isotopes to form reversible hydrides offer several advantages for storing and processing tritium. Advantages include safe, low pressure, high density storage, and delivery of high purity 3He-free tritium without the use of pumps. As part of a program to devleop metal hydride technology for storing and processing tritium, the effects of tritium aging on the thermodynamic behavior of the tritides are under investigation. During aging of LaNi4.25Al0.75 tritides, the 3He decay product of tritium produced in the lattice does not leave the lattice but causes changes in the thermodynamics of the gas-solid system. Among the changes noted are (1) decreased tritium desorption pressures, (2) increased slopes of desorption isotherm plateaux and (3) small quantities of irreversibly-held tritium. Absorption-desorption cycling and brief heating of samples to 350°C while loaded with deuterium partially reverses these effects. While the desorption isotherms of tribium-aged LaNi4.25Al0.75 tritides resemble the desorption isotherms of amorphous hydrogen storage materials, X-ray diffraction patterns of tritium-aged samples after desorption of tritium do not exhibit the characteristics of an amorphous material. The diffraction patterns show broadening and anisotropic effects that suggest the presence of lattice strains and orientational effects of 3He in the LaNi4.25Al0.75 lattice. Self-interstitials, dislocations and bubbles are probably present in the aged samples.
The electrical conductivite of the solid chain Pt-beta-Ta2O5-Pt was studied by means of electrical impedance spectroscopy in the temperature range 1223-1523 K and the partial pressure of oxygen Po2 range 10(-18)-1 atm. Impedance data analysis yielded an equivalent electrical circuit including three parallel branches, characteristic of mixed conduction. The dependence of R(e) and R(i), the electronic and ionic resistances, on Po2 and temperature is in good agreement with Frenkel's hypothesis of anionic disorder (V0,2. O(i)2) and the presence of M(Ta)3' divalent impurities. Isothermal variations of ionic number transport as a function of Po2 were determined.
In this work, the nearest neighbor distance between two deuterium atoms in an f.c.c. palladium lattice was estimated by taking into account the effect of an electronic screening cloud. The lattice was assumed to contain a deuterium atom at the nearest neighbor octahederal site to a vacancy, and the potential energy field experienced by another deuterium atom was constructed by a pair potential technique. In this resulting field, the Schrodinger equation for another deuterium atom was solved, and the distance between two neighboring deuterium atoms was estimated. Our result for the distance was about 0.66 angstrom, which is smaller than the molecular value of 0.74 angstrom.
The properties of four hydride-forming materials have been investigated to determine their applicability for use in a process to separate hydrogen isotopes from inert gases. These materials are Zr0.8Ti0.2Ni, Zr0.65Ti0.35Co, NdCo3 and ErFe2. The properties investigated while surveying these materials include ease of activation, isotherm characteristics, kinetics, cycling stability and oxygen stability. The results of the survey indicate NdCo3 to be the hydride former of choice for use in the inert gas separation process. It is the most easily activated and has the most favorable isotherm characteristics (the largest usable capacity, flat plateaux, small hysteresis and negligible heel) as well as the fastest absorption kinetics of the materials tested. NdCo3 also has good cycling and oxygen stability.As with most intermetallic alloys, NdCo3 decrepitates into a fine powder after only a few sorption cycles in hydrogen and therefore must be consolidated in order to be used in the fixed bed absorber envisioned for the inert gas separation process. Consolidation was achieved through support of the NdCo3 in a sinter-bonded aluminum matrix. Stable compacts of NdCo3 have been made consisting of 40 wt.% Al in NdCo3 pellets, pressed at 186 MPa and sintered under vacuum for 2 h at 450-degrees-C. These compacts retained the full absorptive capacity of NdCo3 and remained 99 wt.% intact after 15 sorption cycles in hydrogen.
Structural parameters, i.e. number of near neighbours and bond distances, in the first coordination shell have been determined in Samarium Schiff-base complexes of 2-banzoyl-pyridine benzolhydrazone Sm(L)3, 2-benzoyl-pyridine salicyloylhydrazone Sm(LH)3, a few known compounds of gadolinium, and its nicotinate and glycolate complexes. In the Sm(L)3 and Sm(LH)3 complexes it is found that samarium has nine near-neighbours at an average distace of 2.41 ± 0.03 Å. Analysis of X-ray absorption fine structure at the gadolinium LIII edge shows that gadolinium is coordinated to eight oxygen neighbours at a distance of 2.43 ± 0.03 Å in its nicotinate complex.
CALPHAD analysis of a number of GaAs-Me and GaAs-MeB2 systems was performed to identify attractive eutectic systems which could be solidified to obtain regular rod-like structures for synthesis of new composite electronic materials for high power switching. The calculations, which are based on the explicit definition of the thermochemical properties of multicomponent liquids and compound phases, provide a means for predicting the eutectic temperatures and compositions. Moreover, component activities, vapor pressure and compatibility with encapsulants can also be predicted.
Amorphous FeGd alloys, from 16 to 70 at.% Gd, were prepared with a melt-quenching method in a vacuum. An X-ray diffraction study on the crystallization process showed that these amorphous alloys crystallized into two phases, that is the h.c.p. Gd phase and the Laves phase (F2Gd). Mössbauer measurements of the amorphous phases showed that the internal hyperfine field was at its maximum of 276 kOe in the neighborhood of 42 at.% Gd. The isomer shifts were about + 0.1 mm s−1.
A study was carried out of the processes occurring during chlorination of CuO and Cu2O with chlorine or a mixture of CO and Cl2 in a temperature range in which only solid products are formed.The reaction rate was studied at different temperatures, and in the presence or absence of reductants, by the thermogravimetric method.It was shown that the reaction products have a pronounced blocking influence on further chlorination processes. The maximum degrees of conversion of CuO and Cu2O are equal to 0.06 and 0.3 respectively. The sequence of formation of chlorination products, as found by X-ray analysis, was CuOCl2, CuCl, CuCl2 and CuO.
Bei der Umsetzung von Pr2Se3 mit Natrium wurden die Verbindungen NaPr8Se12 und NaPr2Se3 in Pulverform erhalten. Die dargestellten Verbindungen wurden analytisch und röntgenographisch charakterisiert. NaPr8Se12 ist von schwarzer Farbe und kristallisiert im Th3P4-Typ (Raumgruppe, I4̄3d; Z = 43, a = 8,9095(4) Å). NaPr2Se3 besitzt eine dunkelblaue Farbe und kristallisiert im NaCl-Typ (Raumgruppe, Fm3m; Z = 43, a = 5,974(1) Å). In den Verbindungen tritt Praseodym in den ungewöhnlichen Oxidationsstufen + 2,875 bzw. + 2,5 auf.
