S.M. Filipek

Structural and magnetic properties of RFe2H5 hydrides (R=Y, Er)

The structural and magnetic properties of RFe 2 hydrides (R=Y, Er) synthesized under high hydrogen pressures of 10 kbar and 373 K, have been investigated. Both saturated RFe 2 H 5 hydrides absorb about 5 H/f.u. and crystallize in the same type of orthorhombic structure (Imm2 space group), with a=5.437(1) A, b=5.850(1) A and c=8.083(1) A for YFe 2 H 5 and a=5.424(1) A, b=5.793(1) A and c=8.009(1) A for ErFe 2 H 5 . The large hydrogen pressure, necessary to reach 5 H/f.u. can be attributed to a partial filling of all types of available interstitial sites. YFe 2 H 5 displays a weak ferromagnetic behavior, which is almost independent of the temperature. ErFe 2 H 5 shows also a weak magnetization at high temperature whereas below 20 K its magnetization sharply increases due to Er magnetic ordering.

Neutron diffraction study of ZrM2Dx deuterides (M=Fe, Co)

Abstract The structure of ZrFe2 and ZrCo2 deuterides prepared under very high deuterium pressure has been studied by neutron diffraction (ND) at 10 K. The patterns of both compounds are refined with a mixture of intermetallic compound and deuteride. For ZrFe2Dx, the cell volume increases with 23% and the 2.7 D/f.u. are located randomly in A2B2 sites. The Fe moments order in a ferromagnetic structure and increase from 1.8 to 2.2 μB/Fe upon D absorption. The ZrCo2 deuteride shows a doubling of the cell parameter due to deuterium order of 2 D/f.u. in 7 over 12 A2B2 sites with a cell volume increase of 12%.

The kinetics of hydrogen transport through amorphous Pd82−yNiySi18 alloys (y=0–32) by analysis of anodic current transient

Hydrogen transport through amorphous Pd82−yNiySi18 alloys (y=0–32) was investigated in 0.1 M NaOH solution by analysis of the anodic current transient. It was found that the anodic current transient shows the non-Cottrell behaviour, but its shape and value remain nearly constant regardless of the hydrogen discharging potential. From the coincidence of the anodic current transient theoretically calculated with that experimentally measured, it is suggested that the change in surface concentration of hydrogen with time is uniquely given by the rate of hydrogen transfer from absorbed state at the electrode sub-surface to adsorbed state on the electrode surface. This means that neither the ‘constraint of constant concentration’ nor the ‘constraint by Butler–Volmer behaviour’ is effective at the electrode surface during hydrogen extraction. On the basis of the theoretical current–time relation under the ‘constraint by hydrogen transfer of absorbed state to adsorbed state’, the hydrogen diffusivity was determined to have an almost constant value of (1.3±0.4)×10−8 cm2 s−1, irrespective of the Ni content and in the absence of Ni. On the other hand, it is inferred that the rate constant of hydrogen transfer decreases markedly with increasing Ni content due to the Ni(OH)2 layer formed on the electrode surface.

Structural and magnetic properties of ErFe2D5 studied by neutron diffraction and Mössbauer spectroscopy

A neutron powder diffraction study of ErFe2D5, synthesized under 1 GPa hydrogen pressure, shows that it crystallizes at room temperature in an orthorhombic structure described by the Pmn21 space group with a = 5.42 A, b = 5.79 A, c = 8.00 A. The deuterium atoms order preferentially in some A2 B2 and AB3 interstitial sites. Below 5 K the erbium moments order in a canted magnetic structure, with an erbium moment of 6.6 μB at 1.4 K. The 57Fe Mossbauer spectra of ErFe2D5 from 4.2 to 300 K indicate that there are no ordered Fe moments at zero field. These results are discussed in relation to the influence of hydrogen absorption on the magnetic interactions.

The influence of hydrogen absorption on the electrical resistance and thermopower of some PdSibased metallic glasses

Abstract The electrical resistance and thermopower of amorphous Pd 83 Si 17 , Pd 79 X 4 Si 17 and Pd 73 X 10 Si 17 ( X = Ag , Co , Cr , Cu , Fe , Ni ) were measured as functions of the hydrogen pressure in the range 1 bar–20 kbar. The electrical resistance of some of these alloys was measured as a function of the deuterium pressure in the range 1 bar–0.8 kbar. A distinct isotope effect was found. In most cases the absolute thermoelectric power is a linear function of the logarithm of hydrogen fugacity and thus is a linear function of the chemical potential of gaseous hydrogen. The electrical resistance exhibits a non-linear dependence on the chemical potential of hydrogen or deuterium in all cases. No discontinuities were observed in either property in the total pressure range. Hysteresis was observed during absorption and desorption, with increasing values at higher pressures. This suggests local restructuring in the glassy matrix as a result of the presence of hydrogen atoms. No evidence of saturation behaviour was obtained. All the measurements were carried out at 25 °C.

Search for “cold-fusion” in some MeD systems at high pressures of gaseous deuterium

Abstract Metallic palladium and nickel were treated with gaseous deuterium at 298 K to pressures of 3.1 GPa and 1.0 GPa respectively. The high concentrated deuterides did not exhibit, at long time equilibrium as well as in dynamic conditions, evidence of neutron emission nor evolution of heat due to possible “cold fusion”. The volume concentrations of deuterium definitely exceeded those achieved by electrolytic charging. Electrical resistance measurements of palladium deuteride up to 3.1 GPa of gaseous deuterium indicated a further uptake of deuterium above the estimated stoichiometry of octahedral vacancies. A partial filling up of tetrahedral vacancies probably takes place. Electrolytic charging in high pressures of gaseous deuterium did not improve the negative observations above. Thus the observations of Fleischmann and Pons are not confirmed at higher volume concentrations of deuterium in the palladium and nickel lattice as well in equilibrium as in dynamic conditions (phase transitions, high pressure electrolysis).

Some properties of amorphous pd-si and pd-ni-si alloys under hydrogen pressures of up to 2 GPa ☆

Abstract The electrical resistance and thermoelectric power of amorphous Pd 85 Si 15 , Pd 83 Si 17 , Pd 82 Si 18 ) Pd 72 Ni 10 Si 18 , Pd 62 Ni 20 Si 18 and Pd 50 Ni 32 Si 18 were measured as functions of the hydrogen pressure up to 2 GPa. The equilibrium values of the hydrogen concentration at hydrogen pressures of 60 MPa, 1.4 and 2.1 GPa were determined for each sample investigated. Hysteresis was observed during absorption-desorption cycling for all the Pd-Si alloys and for Pd 72 Ni 10 Si 18 . Pd 85 Si 15 and Pd 83 Si 17 became saturated with hydrogen at hydrogen-to-palladium ratios of 0.45 and 0.36 respectively and then exhibited superconducting behaviour with T c = 1.6 K .

Electrical resistance of some alkaline earth metal hydrides and alkali metal aluminium hydrides and borohydrides under high pressure

Abstract The electrical resistances of alkaline earth metal hydrides (CaH2, SrH2 and BaH2) and alkali metal aluminium hydrides and borohydrides (LiBH4, NaBH4, RbBH4 and LiAlH4) were measured to 16 kHz in a Bridgman anvil device at room temperature at pressures up to 140 kbar using pressed powdered samples. A more or less continuous decrease in the electrical resistance as a function of pressure was observed in all alkaline earth hydrides. A similar behaviour is exhibited by LiAlH4. Contrary to this behaviour, the alkali metal borohydrides show a minimum in the electrical resistance in the low pressure range and a further increase at higher pressures. The steepness of this increase in LiBH4 and NaBH4 suggests a phase transition in the pressure range between 20 and 30 kbar.

Synthesis of novel deuterides in several Laves phases by using gaseous deuterium under high pressure

New deuterides of Laves phases: ErFe2D5, YFe2D5, ZrFe2D3.5 and ZrCo2D2, have been obtained by using of gaseous deuterium at high pressure. A new orthorhombic structure was found for ErFe2D5 and YFe2D5, while ZrFe2D3.5 and ZrCo2D2 were formed with a large expansion of the initial C15 cubic lattice. Formation of hydrides with high hydrogen concentration substantially changes the magnetic properties of ErFe2 and YFe2 but has no significant influence on the magnetization of ZrFe2. The possibility of the formation of new deuterides (hydrides) in ZrCr2 and YMn2 has also been confirmed.

Structural, thermal and magnetic properties of ErMn2D6 synthesized under high deuterium pressure

An ewphase of ErMn2D6 has been prepared by applying high hydrogen pressure on C14 ErMn2 .T hisphase is isostructural to YMn2D6 and crystallizes with a K2PtCl6 type structure havin ga n ordered anion and a partially disordered cation arrangement as Er and half the Mn atoms are randomly substituted in the same 8c site. This hydride is very stable and decomposes into ErD2 and Mn at about 630 K. The reverse susceptibility follows a Curie–Weiss law with an effective moment of 10 µB similar to that of ErMn2 .A lthough a saturation magnetization of 5 µB is measured at 4.2 K, smaller than that of ErMn2 (8 µB), no long range magnetic order is observed in the neutron patterns. Short range magnetic order, corresponding to both ferromagnetic and antiferromagnetic correlations, is observed in the neutron patterns up to 5 K. The chemical disorder of Er and Mn atoms on the 8c site should prevent the long range magnetic order and favour a distribution of Er spin orientation.