Showing papers in "Journal of The Less Common Metals in 1985"

The uses and enigmas of the Al2O3-Y2O3 phase system

Abstract: The uses of the five compounds, namely Al2O3, Y3Al5O12, YAlO3, Y4Al2O9 and Y2O3, which occur in the Al2O3-Y2O3 phase system are reviewed and the uncertainties which have pervaded the existence and stability of the three intermediate phases are discussed. It is shown that the major factor which has resolved these uncertainties is the correlation achieved between phase studies and single-crystal growth data, the latter being prompted by the increased device use of the compounds within this phase system.

Correlations between the structural properties, the stability and the hydrogen content of substituted LaNi5 compounds

Abstract: Thermodynamic and structural properties including electrochemical behaviour of LaNi5 and its β hydride are reviewed. The different structural models of the β hydride are discussed. The variations in the hydriding properties as a result of partial substitution of the constituents are presented. Qualitative and quantitative models that relate hydriding characteristics (stability, hydrogen content) to other physical properties (formation enthalpy, unit cell volume, interstitial hole size, electronic structure) of these intermetallics are briefly reviewed. The contribution of the authors concerning the correlation between the stability and the heat of formation of the intermetallic compounds is presented. The crystal structures of some substituted LaNi5 compounds and related hydrides demonstrate the correlation between the absorption capacity and the number of sites occupied by hydrogen atoms.

The crystal structure of A-Ce2O3☆

Abstract: A single-crystal structure determination of Ce2O3 has been carried out (two-circle diffractometer, Mo Kα radiation, R value 2.9% for 614 unique reflections). The results are in perfect agreement with Pauling's model of the A-type sesquioxides and with the neutron powder diffraction data known for La2O3 and Nd2O3. There is no indication of the so-called micro-twinning which was found 20 years ago by means of single crystals of La2O3 and Nd2O3.

Dielectric behaviour of tetravalent titanium-substituted Ni-Zn ferrites

Abstract: The dielectric constants and dielectric loss tangents of tetravalent titanium-substituted Ni-Zn ferrites Zn 0.25 Ni 0.75 + t Ti t Fe 2−2 t O 4 with various titanium concentrations were measured at room temperature in the frequency range 100 Hz – 500 kHz. The variation of these parameters with composition and frequency is explained qualitatively. Peaks in the dielectric loss tangent versus frequency curves are observed in two of the ferrites. The possible mechanisms are discussed.

Effects of lattice strain on the hysteresis of pressure-composition isotherms for the LaNi5H2 system

Abstract: The effects of annealing on the hysteresis of pressure-composition isotherms for the LaNi 5 H 2 system were examined. It was found that the higher was the annealing temperature before absorption, the higher was the pressure of the subsequent absorption isotherm and eventually the larger was the hysteresis. The dehydrided samples, which were annealed at various temperatures, were subjected to X-ray powder diffraction line profile analysis using the Warren-Averbach method. It was concluded from the results obtained for the crystallite domain size and the lattice strain that the predominant factor affecting the hysteresis is the microstrain in the direction perpendicular to the hexagonal c axis.

The rare earth-titanium (III) perovskite oxides—An isostructural series with a remarkable variation in physical properties☆

Abstract: The rare earth-titanium(III) perovskites, RTiO 3 (R ≡ rare earth), form an isostructural series for R  La to Tm, including Y. Discontinuous changes in electrical and magnetic properties occur as the radius of R decreases. For R  La and Ce, metallic conductivity is observed with metal-semiconductor transitions at low temperatures. All other R are semiconducting with activation energies which increase from 10 −2 eV (Pr, Nd) to 10 −1 eV (Gd, Y). For R  La, Ce, and Pr, antiferromagnetic order occurs below temperatures near 100 K, for R  Nd only paramagnetism is seen and for R  Gd to Tm, including Y, ferromagnetic (R  Y) or ferrimagnetic (R  Gd-Tm) behavior is observed. The above changes can be correlated with the variation of the Ti-O-Ti angle and understood, qualitatively, using the Hubbard model and super-exchange theory.

Preparation and properties of hydrogen storage alloy-copper microcapsules

Abstract: Fine particles of hydrogen storage alloys such as LaNi5 and MmNi4.5-Mn0.5 (Mm  misch metal) were encapsulated in a thin layer of copper 1–2 μm thick by means of a special chemical plating method. This treatment prevented further disintegration of the metal and improved the thermal conductivity. The alloy-copper microcapsules, which had dimensions of less than 30 μm, were able to absorb hydrogen easily without special activation and exhibited no decrease in hydrogen storage capacity. Pellets obtained by compressing the microencapsulated powder under a pressure of 5–10 tf cm−2 did not show any visible cracks after 1000 hydrogen sorption cycles.

A new phase in the Pd-C system formed during the catalytic hydrogenation of acetylene

Abstract: The catalytic hydrogenation of acetylene was studied using X-ray diffraction and gas chromatography. The results obtained show that carbon atoms penetrate into the palladium catalyst during the reaction. This process results in the formation of a highly supersaturated solid solution of carbon in the metal, which for kinetic reasons is stable only at moderate temperatures. The crystallographic structure of the solid solution is analogous to that of palladium, with the lattice constant 2.6% higher. The carbon concentration of 11.5 at.% thus obtained is two orders of magnitude higher than that in the saturated Pd-C solution.

Phase transformations of the LaNi5-H2 system

Abstract: Pressure-composition isotherms have been measured for the LaNi5-H2 system. The isotherms at higher than 80 °C clearly showed two plateaux on desorption, while the gap between two plateaux at the composition LaNi5H≈3 was much smaller in absorption than it was in desorption. In situ X-ray diffraction measurements have been performed at 84 °C in the pressure range up to 4.5 MPa and a new hydride phase corresponding to LaNi5H≈3 was found. The lower plateau on the isotherms is ascribed to the coexisting region of a phase (solid-solution phase) and β phase (LaNi5H≈3) and the higher plateau to that of β phase and 7 phase (LaNi5H6). Changes in lattice parameters have also been measured along these phase transformations. No distortion of the original hexagonal lattice has been observed in the present measurements. The representative lattice parameters for a, β and γ were obtained as follows. α: a = 5.01 – 5.06 A , c = 4.00 A ; β: a = 5.27 – 5.31 A , c = 4.05 – 4.10 A ; γ: a = 5.36 – 5.4 A , c = 4.18 – 4.25 A .

On the site preference of 3d atoms in compounds of the R2(Co1−xFex)14B type

Abstract: L'etude par effet Mossbauer des composes Nd 2 Co 14 B dopes avec du fer montre que les atomes de fer ont une forte preference pour occuper le site 8j 2 . Interpretation des resultats en termes de force relative des liaisons et d'effets dimensionnels

De nouvelles séries de germaniures, isotypes de U4Re7Si6, ThCr2Si2 et CaBe2Ge2, dans les systèmes ternaires RTGe où R est un élément des terres rares et T ≡ Ru, Os, Rh, Ir: supraconductivité de LaIr2Ge2

Abstract: Resume Cinquante un nouveaux germaniures ternaires ont ete caracterises par analyse radiocristallographique de poudres: 19 isotypes de U 4 Re 7 Si 6 : Lu 4 Ru 7 Ge 6 , R 4 Os 7 Ge 6 (R ≡ Er, …, Lu), R 4 Rh 7 Ge 6 (R ≡ Dy, …, Lu) et R 4 Ir 7 Ge 6 (R ≡ Y, Tb, …, Lu); 28 isotypes de ThCr 2 Si 2 : RRu 2 Ge 2 et RRh 2 Ge 2 (R ≡ Y, La, …, Yb), EuIr 2 Ge 2 ; 4 isotypes de CaBe 2 Ge 2 : RIr 2 Ge 2 (R ≡ La, …, Nd). Trois autres restent a preciser: SmIr 2 Ge 2 et TbIr 2 Ge 2 qui semblent isotypes de CaBe 2 Ge 2 mais avec des parametres singuliers; GdIr 2 Ge 2 dont la maille orthorhombique pourrait etre une variante deformee de celles de type CaBe 2 Ge 2 . Les evolutions structurales observees sont discutees. Parmi les isotypes de ThCr 2 Si 2 ou CaBe 2 Ge 2 a l'yttrium et au lanthane, seul LaIr 2 Ge 2 est supraconducteur au-dessus de 1,4 K ( T C = 1,5 K ).

The ternary systems ScAlN and YAlN

Abstract: In the ternary ScAlN system a perovskite-type phase Sc3AlN1 − x (a = 0.4396–0.4435 nm) occurs at 1273 K. This phase is in equilibrium with ScN, Sc(solid solution), Sc2Al and ScAl. AlN does not coexist with scandium but does so with ScN, ScAl2 and ScAl3. The binary phase ScAl was found to be orthorhombic with a = 0.502 99 nm, b = 0.989 45 nm and c = 0.312 63 nm. In the Y-Al-N system no ternary phase was found. AlN reacts with up to 40 at.% Y to yield YN and YAl2. Isothermal sections at 1273 K are presented for both ternary systems.

Structural characterization of new ternary compounds of uranium and cerium

Abstract: The new ternary uranium and cerium compounds UCu4Al8, U2Cu7Al10, URu2Si2, CeCu6.5Al6.5, CeCu2Sn1.9 and CeZn2Al2 have been prepared and structurally characterized.

Magnetic order in ternary compounds RRh2Si2 and RRu2Si2

Abstract: Investigations by neutron diffraction and magnetic measurements are reported on the ternary suicides RRh2Si2 (R  Ce, Nd, Tb) and RRu2Si2 (R  Nd, Tb) with the tetragonal structure of the ThCr2Si2 type. CeRh2Si2 orders antiferromagnetically below 36 K with a wave vector k = [ 1 2 1 2 0] and magnetic moments parallel to the c-axis (m0) = 1.50 μ/Ce). The magnetic structure of TbRh2Si2 is antiferromagnetic (k = [001]) below TN = 94 K, the magnetic moments (8.5 μB/Tb at T = 15 K) are also parallel to the c-axis. NdRh2Si2 has the same magnetic structure below TN = 57 K, with m0 = 2.80 μB/Nd parallel to the c-axis. NdRu2Si2 exhibits a more complicated magnetic structure: below TN = 24 K it develops a sine-wave modulation (k = [0.130.130]) of the magnetic moments always parallel to the c-axis, with an amplitude Ak = 3.23 μB/Nd; a squaring of the magnetic structure occurs at about 15 K (m0 = 2.84 μB), and at T

Investigation of new lanthanum-, cerium- and uranium-based ternary intermetallics

Abstract: While searching for new Ce- and U-based “heavy fermion” systems, we have investigated the following intermetallic compounds: CeCu 2 Ge 2 , CeCu 2 Sn 2 , CeAg 2 Ge 2 , CeZn 2 Al 2 (tetragonal ThCr 2 Si 2 -structure and modifications thereof); CeRu 3 Si 2 , URu 3 Si 2 (hexagonal LaRu 3 Si 2 -structure); Ce 2 Cu 7 Al 10 , U 2 Cu 7 Al 10 (trigonal Th 2 Mn 17 -structure); CeCu 4 Al 8 , CeAg 4 Al 8 , UCu 4 Al 8 (tetragonal CeMn 4 Al 8 -structure); LaCu 13− x Al x with x = 3, 5.5, and 6.5, as well as CeCu 6.5 Al 6.5 (cubic NaZn 13 -structure). Resistive and inductive measurements were undertaken between T = 30 mK and room temperature, and two new superconductors were found: LaCu 6.5 Al 6.5 ( T c = 0.65 K) and CeRu 3 Si 2 ( T c = 1.2 K). The specific heat and thermopower of two of these systems have also been measured. CeCu 4 Al 8 shows interesting features that are presumably related to fine structure in the “heavy-fermion” density of states near the Fermi level. CeCu 6.5 A1 6.5 shows a magnetic transition at T = 0.5 K which resembles a “spin-glass freezing” rather than a formation of long-range magnetic order.

Thermodynamics of lanthanide-organic ligand complexes

Abstract: Some aspects of lanthanide-organic ligand interaction in aqueous solutions are reviewed. Thermodynamic parameters ( ΔG , ΔH and ΔS ) of complexation are interpreted in terms of hydration, inner versus outer sphere character, stability versus chelate ring size and ligand charge polarization.

Vibronic optical transitions in inorganic and organic rare earth materials

Abstract: The lanthanide elements are widely used as optical structural probes in solid state chemistry. Group theory and line positions are used to derive the symmetry and the number of crystallographic sites. For some compounds additional lines or illogical splittings make interpretation difficult. The Stark level widths depend on the phonon density of states in the material: if it is a continuous function the classical theory applies well, but if the phonon density of states is resolved into sharp peaks, zero-phonon line splittings may occur from resonance effects, with sharp phonons corresponding to the energy difference between Stark levels. Examples are shown for lanthanide organic compounds, and for some inorganic phases as well. Vibronic satellites occur prominently in some phases, especially if tetrahedral anions (phosphate etc…) are present. From the vibronics associated with simple electronic transitions it is possible to derive an effective density of phonon states. The puzzling case of Eu3+ in GdNbO4, where the fine structure of the emission spectrum depends on the optical excitation wavelength, is presented.

Hydrogen (deuterium) ordering in the β-LaNi5Dx > 5 phases: A neutron diffraction study

Abstract: A new investigation of the structure of the β-LaNi5Dx deuteride has been performed using neutron diffraction over a wide range of deuterium concentration (5.0 ⩽x ⩽ 6.7). By increasing the deuterium content, we show that the deuteride undergoes a structural phase transformation due to a progressive ordering of D atoms. This results in a reduction of symmetry and in a superstructure which corresponds to a doubling of the LaNi5 unit cell along the c axis. We propose a new model for the structure of β-LaNi5Dx (5.0 ⩽ × ⩽ 7.0) which is described in the P63mc space group. In this model the ordering of deuterium is characterized by a parameter a which varies linearly from zero to one as x increases from 5 to 7 D per LaNi5. In the fully ordered LaNi5D7 phase deuterium would occupy four types of interstitial sites.

The physical metallurgy and processing of sintered rare earth permanent magnets

Abstract: Rare earth permanent magnets are estimated to account for more than 10% of the sales value of the total world permanent magnet production. These magnets are used in a wide range of applications; particularly in those weight- and volume-conscious applications where use is made of their high energy products to achieve miniaturization of the permanent magnet device. The aim of this paper is to review the development of rare earth permanent magnets. The metallurgy and origin of the magnetic hardness of RCo 5 and R 2 Co 17 (R ≡ rare earth) SmCo-based permanent magnets are described. The recent developments of permanent magnets based on Nd 2 Fe 14 B are outlined. The processing of SmCo- and NdFeB-based permanent magnets is described and differences between their behaviour during processing are highlighted. Finally, the improvement and future development of NdFeB and related permanent magnets are discussed.

Critical survey of rare-earth borides: Occurrence, crystal chemistry and physical properties☆

Abstract: The six families of binary rare-earth (RE) borides are reviewed: REB 2 , REB 4 , RE 2 B 5 , REB 6 , REB 12 and REB ~66 . The existence of these compounds and their crystal structures are discussed knowing that metal atoms contribute both geometrically and electronically to the stabilization of the electron-deficient boron framework. Emphasis is focused on the ability of metal or non-metal impurities either to stabilize a particular structure or to modify drastically the electrical and magnetic properties of the borides. Hexaborides are chosen to illustrate this point. The physical properties of some significant compounds are highlighted: ErB 4 and HoB 4 (magnetic phase transition), YbB 4 , YbB 12 and SmB 6 (intermediate-valence state), CeB 6 (dense Kondo-like behaviour), EuB 6 (ferromagnetic semiconductor), LaB 6 (thermoelectronic emitter) and YB 6 (superconductor).

Electrical conductivity of NiZn ferrites doped with Ti4+ ions

Abstract: The d.c. resistivity ρ of the polycrystalline solid solutions Zn0.25Ni0.75 + t−TitFe2−2tO4 was measured as a function of titanium content and temperature. The electrical conduction in these ferrites is explained on the basis of the hopping mechanism. The composition dependence of the resistivity is explained in terms of the cation distribution. The activation energy of each sample is calculated from the plots of log ρ versus 10 3 T which are almost linear.

The economics of rare earths

Abstract: The rare earths community is small and restricted and needs better communication between production, end users, and research. This paper gives a general overview of RE reserves, production capacity, and also a breakdown of the consumption by end users. Among the permanent problems of RE producers, three are of greatest importance: 1. (i) Balancing the market demand with the natural occurrence of the RE elements in most common ores such as monazite and bastnasite. This is essential in ensuring the lowest market price for any RE element. 2. (ii) The extreme speed of development of some new applications. 3. (iii) The difference in growth rates of various applications.

The “solid angle sum rule”: A new ligand cone packing model of optimal applicability in organolanthanoid chemistry, part I

Abstract: As a result of the systematic evaluation of about forty published molecular structures of organolanthanoid(III) complexes, the so-called “solid-angle-sum (SAS) rule” suggests that optimal coordinative saturation is verified for the comparatively small SAS value of 0.73. Here, 4π·SAS is the sum of the individual solid angles of all ligands surrounding one central metal ion (Ln3+). On the basis of empirical standard values of the “solid angle factors”, SAF = SA 4π , of various frequently occurring ligands, the SAS-rule allows reasonable predictions to be made of the relative stabilities of distinct members of numerous complex families, particularly as a function of the ionic radius of the respective central metal ion (including also La3+, Y3+ and Sc3+).

Thermodynamics of Ni-Cr-Al alloys

Abstract: An isothermal section of the Ni-Cr-Al system at 1423 K has been investigated using Knudsen cell mass spectrometry to determine the activities of nickel, chromium and aluminium. These data provide independent measurements, i.e. without the need for integration, of all of the components, both in the binary and ternary systems. The data on the binaries are mutually consistent, as can be seen by the comparisons given between the experimental results and values obtained by integration.

High Pressure X-Ray Investigation of the Alkali Hydrides NaH, KH, RbH, and CsH*

Abstract: The interest in the alkali hydrides has been generated by their crystallochemical similarity to the alkali halides. Bashkin et al. [1] have pointed out, that as in the case of most alkali halides with NaCl-type structure, the alkali hydrides may also undergo a structural phase transition to a CsCl-type structure when high pressure is applied. They have found such a transition in KH at about 4 GPa and have predicted that this transition is thermodynamically possible also in NaH, RbH, and CsH, but not in LiH. The aim of our high pressure energy dispersive X-ray study was to confirm this prediction experimentally for the alkali hydrides, which should transform to the CsCl-type structure and to determine the equations of state in both phases of these alkali hydrides.

Anti-glass phases and other lanthanide tellurates with fluorite-related structures

Abstract: Two series of metastable, cubic face-centered non-stoichiometric anti-glass tellurates of Y, La, and lanthanides have been found: Te-richer phases, containing tetravalent Te only, with compositions between Ln 2 Te 6 O 15 and Ln 4 Te 7 O 20 and lattice constants of 570−549 pm, and Ln-richer phases containing minor amounts of hexavalent Te, with Ln:Te ratios between 3:2 and 11:10, and lattice constants between 574 and 539 pm.

Ternary 1:1:1 alloys of nickel and palladium with tin and rare earths

Abstract: Ternary alloys of the rare earths (R) with tin and nickel or palladium in the stoichiometric ratio 1:1:1 were studied. It was confirmed that these alloys have structures belonging to the CeCu2 family (oI12 (CeCu2) or oP12 (TiNiSi) types). The behaviour of the average atomic volumes of these phases is compared with the behaviour of other series of similar compounds, and the general properties of several RTSn alloys are briefly summarized.

De nouvelles séries de germaniures, isotypes de Yb3Rh4Sn13 et BaNiSn3, dans les systèmes ternaires TRTGe où TR est un élément des terres rares et T ≡ Co, Rh, Ir, Ru, Os

Abstract: Resume Quarante-sept nouveaux germaniures ternaires ont ete caracterises par analyse radiocristallographique de poudres: 34 isotypes de Yb 3 Rh 4 Sn 13 : TR 3 Co 4 Ge 13 (TR ≡ Y, Sm, Gd, …, Lu), TR 3 Rh 4 Ge 13 (TR ≡ Y, Nd, Sm, Gd, …, Lu) et TR 3 Ir 4 Ge 13 (TR ≡ Y, Ce, …, Sm, Gd, …, Lu), et 13 isotypes de BaNiSn 3 : TRCoGe 3 (TR ≡ La, …, Nd, Eu), TRRhGe 3 (TR ≡ La, …, Pr, Eu), TRIrGe 3 (TR ≡ La, Eu), LaRuGe 3 et LaOsGe 3 . Les evolutions structurales observees sont discutees.

Low-temperature magnetic and electrical properties of the new ternary silicides LaMSi3 and CeMSi3 with M ≡ Co, Rh, Ir, Ru, Os

Abstract: The low-temperature magnetic susceptibilities and electrical resistivities of a new family of ternary suicides of general formula RMSi 3 are described. These compounds, where R ≡ La or Ce and M ≡ Co, Rh, Ir, or Ru and Os crystallize in the BaNiSn 3 structure. LaRhSi 3 and LaIrSi 3 are found to be superconducting with T c ∼- 2.5 K. In CeRhSi 3 and CeIrSi 3 , the Ce valence is close to 3 and these compounds are Kondo-lattice systems. An anomaly occurs in their susceptibilities at ∼-2 K and 5 K, respectively, accompanied by a sudden change from T to a T 2 regime in their resistivities. At the other end of the series, CeCoSi 3 behaves like a normal metal and becomes superconducting below T c ∼- 1.2 –1.4 K.