Ya. M. Kalychak

Short hydrogen–hydrogen separations in novel intermetallic hydrides, RE3Ni3In3D4 (RE=La, Ce and Nd)

Abstract Crystal structure data for deuterides RENiInD x (RE=La, Ce and Nd) are provided on the basis of high-resolution powder X-ray and neutron diffraction data. The materials retain the hexagonal ZrNiAl type structure on deuteration. The formation of saturated deuterides is connected with anisotropic expansion along [001]. In the saturated hydrides, RE 3 Ni 3 In 3 D 4 , hydrogen atoms are located inside RE 3 Ni tetrahedra that share a common face, thereby forming a RE 3 Ni 2 trigonal bipyramid. This results in extraordinary short H–H separations of around 1.6 A. This feature is unique among well characterised metal hydride materials and is in striking contrast with the generally obeyed empirical rule of 2.0 A for H–H separations. On heating, the saturated materials release half of their hydrogen content at low temperatures, thereby statistically filling just one out of the two neighbouring tetrahedra. The remaining, more strongly bonded hydrogen, is released below 500°C under dynamic vacuum.

Composition and crystal structure of rare-earths–Co–In compounds

Abstract Data about the composition and crystal structure of the known 66 ternary compounds in rare-earths–Co–In systems have been generalized. Some of their peculiarities and relationships to other structure types have been examined.

Hydrides of the RNiIn (R=La, Ce, Nd) intermetallic compounds: crystallographic characterisation and thermal stability

LaNiInH2.0, CeNiInH1.8 and NdNiInH1.7 intermetallic hydrides were synthesised by the reaction of gaseous hydrogen with RNiIn compounds at 298 K and hydrogen pressures 1–100 bar and characterised by X-ray diffraction and thermal desorption studies. The hexagonal symmetry of the initial ZrNiAl-type structure is not changed on hydrogenation. Hydrogen insertion causes a pronounced anisotropic expansion of the unit cells along [001] (Δc/c=14.9–18.3%) and results in a volume increase of 8.9–9.3%. Possible interstitial sites for the accommodation of hydrogen atoms in the lattices of dihydrides RNiInH1.7–2.0 were proposed. A reversible formation of equiatomic RNiIn ternaries accompanies a complete hydrogen desorption from the dihydrides and takes place at temperatures near 800 K. Hydrogen evolution proceeds through two steps with peaks at 425–540 and 630–710 K and at temperatures 500–600 K leads to the formation of lower hydrides LaNiInH0.9, CeNiInH0.8 and NdNiInH0.85, which were structurally characterised as isotropically expanded ZrNiAl-type compounds. The melting points were determined for the LaNiIn (1057 K) and CeNiIn (1083 K) intermetallics. The NdNiIn compound exhibits high thermodynamic stability and does not disproportionate in hydrogen at PH2=1 bar up to 1023 K. RNiIn compounds formed with Y or the heavier rare earth metals (R=Sm, Gd, Tb, Dy, Ho, Er and Tm) do not form hydrides at hydrogenation pressures up to 100 bar, both at room temperature or on heating in hydrogen gas up to 1143 K.

Peculiarities of the composition and structure of the compounds of the rare-earth—NiIn systems

Abstract Data on the composition and structure of 117 ternary compounds of the rare-earth metals, nickel and indium were generalized. Relations between the structure, the metric parameters of the unit cell and valence state of the atoms were considered.

Crystal structure of R2Ni2Pb (R=Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) compounds

Abstract The crystal structures of the R 2 Ni 2 Pb (R=Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) compounds were determined using X-ray powder diffraction. The investigated compounds crystallize with Mn 2 AlB 2 structure type (space group Cmmm , Pearson code oC10 ).

Crystal structure of RNiPb (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) compounds

The crystal structures of the RNiPb (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) compounds were determined using X-ray powder diffraction. The investigated compounds crystallize with a TiNiSi structure type (space group: Pnma, Pearson code: oP12).

Crystal structure and properties of YbAg2In4 and CaAg2In4 compounds

Abstract The crystal structures of the YbAg 2 In 4 and CaAg 2 In 4 compounds have been determined by means of the single crystal method (DARTCH-1 automatic diffractometer, graphite-monochromatized Mo Kα radiation, θ −2 θ scan mode). They belong to a new structure type (space group I m 3, Z =24, a =1.5362(3) and 1.5454(4) nm, respectively). Peculiarities of the defects on the silver atom positions in the structures and their relations to the YCd 6 and YbCd 6 structures are discussed. The magnetic susceptibility of the YbAg 2 In 4 compound follows the Curie–Weiss law in the temperature range 78–293 K. The ytterbium atoms in this compound have an intermediate valence state ( μ eff =2.3 μ B ). The CaAg 2 In 4 compound is a Pauli paramagnet. The electrical resistivity of the studied compounds, measured between 78 and 360 K, is characteristic of a metallic material.

Crystal structure of R12Ni6Pb (R=Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho) and R12Co6Pb (R=Y, La, Pr, Nd, Sm, Gd) compounds

Abstract The crystal structures of the R 12 Ni 6 Pb (R=Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho) and the R 12 Co 6 Pb (R=Y, La, Pr, Nd, Sm, Gd) compounds were investigated by powder X-ray diffraction method. They crystallize with Sm 12 Ni 6 In structure type (space group Im3 , Pearson code cI38 ).

Crystal structure of the new ternary indide CePt2In2 and the isostructural compounds RPt2In2 (R=La, Pr, Nd)

Abstract The title compounds have been synthesized by arc melting of the elemental components and subsequent annealing at 870 K. The crystal structure of CePt 2 In 2 was determined from single-crystal X-ray data ( R =0.0437 for 1439 | F | values and 62 variables). It represents a new structure type of intermetallic compounds: P2 1 /m, mP20, a =10.189(6), b =4.477(4), c =10.226(6) A, β =117.00(5)°, V =416.1(1) A 3 , Z =4. Isostructural compounds have been found also for La, Pr, and Nd.

Magnetic and electrical properties of RCu5.1In6.9 compounds

Abstract Magnetic and electrical properties of the RCu 5.1 In 6.9 compounds with R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er were investigated in the temperature range 4.2–300 K. Additionally, for the compounds of Gd, Tb and Dy exhibiting magnetic anomalies at low temperatures, the magnetization versus magnetic field up to 14 T was measured at 4.2 K. Investigated compounds follow the Curie–Weiss law with relatively small values of the paramagnetic Curie temperature and the values of effective magnetic moment being in fair agreement with the values for the free ions. The electrical resistivity exhibits metallic character. The results are discussed in terms of the differences and similarities with other rare earth intermetallics.