Orthorhombic Zr Research Articles

Magnetic hardening of Zr2Co11:(Ti, Si) nanomaterials

Abstract The role of Ti and Si additions in the magnetic hardening of rapidly-quenched Zr 2 Co 11 -based nanomaterials has been investigated. Nanocrystalline Zr 17 − x Ti x Co 83 and Zr 18 Co 82 − y Si y are mainly composed of rhombohedral Zr 2 Co 11 and a small amount of orthorhombic Zr 2 Co 11 , hcp Co and cubic Zr 6 Co 23 . Ti addition decreases the mean grain size of the magnetic phases, and thus increases coercivity and energy product from 1.6 kOe and 1.9 MGOe for x = 0 to 2.6 kOe and 3.9 MGOe for x = 2, respectively. Si addition enhances the anisotropy field of the hard phase which increases the coercivity but slightly decreases the magnetization. This work shows that Ti has a positive effect on energy product through refinement of structure.

Effects of annealing on Zr 8Ni 19X2 ( X = Ni, Mg, Al, Sc, V, Mn, Co, Sn, La, and Hf): Structural characteristics

The effects of an 8-h annealing treatment at 960 °C on the phase structures of a series of partial-Ni substituted Zr 8Ni 21 alloys, potential metal hydride candidates for high-rate nickel/metal hydride batteries, were studied. The substitution elements included Mg, Al, Sc, V, Mn, Co, Sn, La, and Hf. Only the main phase of the annealed Sn-substitution remained Zr 8Ni 21-structured while those of other substitutions turned into Zr 7Ni 10 or Zr 2Ni 7. Similar to the preference of C14/C15 main phase in AB 2 alloys, the number of outer-shell electrons played an important role in determining the main phase of the A 8B 21 alloys. As the number of outer-shell electrons of the substituting element increased, the main phase evolved from tetragonal Zr 7Ni 10 (Mg, Al, and Sc), to orthorhombic Zr 7Ni 10 (La and Hf), cubic Zr 2Ni 7 (V, Mn, Co, and Sn (before annealing)), and finally triclinic Zr 8Ni 21 (Ni and Sn (after annealing)). After annealing, the abundance of the predominant phase increased, and the number of secondary phases diminished. The only exception was the Sn-substituted alloy, where the major phase transformed from Zr 2Ni 7 to Zr 8Ni 21 (after annealing). In this study, several alloys showed an X-ray diffraction peak at around 38.4°, which cannot be correlated to any phase in the database. The stoichiometry of this phase is close to Zr 2Ni 7 according to X-ray energy dispersive spectroscopy.

Structure and crystallization of the partially crystalline Zr76Ni24 metallic glass

Abstract The partially crystalline Zr 76 Ni 24 (numbers indicate at.%) metallic glass was prepared by melt spinning. The structure and crystallization of the partially crystalline Zr 76 Ni 24 metallic glass during heat treatment at different heating rates have been investigated by means of differential scanning calorimetry in the temperature interval from 300 to 823 K and by X-ray powder diffraction (XRD) at room temperature. According to the XRD results, it was found that two sides of the quenched ribbons showed different structures. The XRD pattern of the side of the ribbon which was in contact with the wheel of the quenching apparatus shows a broad maximum corresponding to an amorphous phase. On the other hand, the XRD pattern of the side of the ribbon which was in contact with the inert atmosphere consists of a set of sharp lines. These lines were indexed and found that they belong to the orthorhombic Zr 3 Ni metastable crystalline phase. Crystallization studies showed that the existence of the orthorhombic Zr 3 Ni metastable crystalline phase does not change the thermal stability of the amorphous phase against further crystallization and remains unchanged during the annealing up to 823 K.

Optical and electronic properties of magnetron sputtered ZrN x thin films

The optical properties of sputtered ZrN x films with 0.81≤ x≤1.35 have been investigated and interpreted in terms of stoichiometry-related defects and crystal structure. The optical properties were determined by optical reflectivity, transmission and spectroscopic ellipsometry. As x increases from 0.81 to 1.35, the optical properties continuously change from metallic to semiconducting behavior. The experimental results have been fitted with a model dielectric function based on a set of Drude–Lorentz oscillators in order to separate the contributions due to free carriers and interband transitions. The effective density N* of conduction electrons decreases from N*=4.9×10 22 cm −3 to N*=2.9×10 21 cm −3 as x is increased from 0.81 to 1.29. The charge carrier scattering time increases from 4.9×10 −16 to 2.6×10 −15 s for 0.81< x≤0.98, and decreases from 2.6×10 −15 to 3.3×10 −16 s for 0.98< x≤1.29. The ZrN x films with x>1.3 are poorly crystallized. In this composition range, the compounds exhibit a crystal structure close to orthorhombic Zr 3N 4; they are insulating with optical absorption coefficients in the range of 2×10 4 cm −1 below 2 eV and an optical absorption onset at 2.3 eV.

Neutron diffraction studies of Zr-containing intermetallic hydrides with ordered hydrogen sublattice. II. Orthorhombic Zr 3FeD 6.7 with filled Re 3B-type structure

Zr 3FeD 6.7 was obtained by deuteration of the Zr 3Fe binary intermetallic compound with Re 3B-type structure at temperatures near 273 K and D 2-pressures below 0.25 bar, and was characterised by Thermal Desorption Spectroscopy and powder X-ray diffraction. Crystal structure data (new structure type of intermetallic hydrides) were derived at 7 K and 293 K from Rietveld refinements of high-resolution powder neutron diffraction data. The orthorhombic symmetry of Zr 3Fe (space group Cmcm) is retained during hydrogen absorption; however, there is an anisotropic expansion in the unit cell dimensions. At 293 K a=3.5803(3); b=11.059(1); c=9.6486(8) Å (Δ a/ a=7.7%, Δ b/ b=0.8%, Δ c/ c=9.4%). The deuterium atoms take an ordered structure with near complete filling of four different types of interstices, one trigonal bipyramidal Zr 3Fe 2 interstice and three types of tetrahedral interstices of Zr 3Fe (one) and Zr 4 (two). Metal–deuterium bond distances are in the range Zr–D=2.058–2.204 Å, Fe–D=1.713–1.791 Å (293 K). All D–D distances in the completely ordered hydrogen sublattice exceed 2.01 Å. The sublattice is built from two types of polyhedra which surround zirconium atoms, consisting of deformed cubes with an additional ninth vertex [Zr1D 9] and deformed cubes [Zr2D 8]. These polyhedra form a spatial framework by sharing vertexes and edges. There are no indications for magnetic long range order in the powder neutron diffraction data at 7 K. A multistaged deuterium desorption starts just above room temperature for Zr 3FeD 6.7. At 448 K the less saturated deuteride Zr 3FeD ∼5, with a reduced unit cell volume, is obtained. Deuteration, when performed at 873 K and 1 bar D 2, results in disproportionation of Zr 3Fe into ZrD 2 and ZrFe 2. Both for Zr 3FeD 6.7 and the disproportionated phase mixture, deuterium desorption under secondary vacuum conditions is completed below 973 K and results in a full recovery of the Zr 3Fe intermetallic. Zr 3Fe presents a new example of successful application of the Hydrogenation–Disproportionation–Desorption–Recombination process to intermetallic phases of zirconium.

Neutron diffraction study of the Tb 3Mn 4Ge 4 compound

The antiferromagnetic Tb 3Mn 4Ge 4 compound (orthorhombic Zr 3Cu 4Si 4-type structure) has been studied by magnetization measurement and neutron diffraction. The Mn magnetic framework is built of antiferromagnetic MnMn zig-zag chains aligned along [001] ( μ Mn = 3.36(9) μ B at 2 K). The two terbium crystallographic sites are characterized by different magnetic behaviours. The terbium in the 2d position, surrounded by a ferromagnetic Mn environment, displays a rather large ordered moment at 300 K ( μ Tb = 3.66 μ B) while the ordered moment of the terbium in the 4e position, in a more complicated environment, gets a significant value only at low temperature. The Tb moments are close to their theoretical values at 2 K. The magnetic behaviour of the Mn sublattice is discussed and compared to the magnetic behaviour observed in the related TbMnGe and RMnGe (R=LaNd) compounds.

The First Mixed-Halide Zirconium Cluster Compounds: Zr6Cl1.6I10.4Be, Zr6Cl1.3I10.7B, and Zr6Cl11.5I1.5B. Matrix Effects and Halogen Substitution in Compact Network Structures

Investigations of the effect of halogen size on structure stability have been conducted in well-reduced and heavily interbridged zirconium chloride-iodide cluster systems. The title compounds are obtained in good yields from reactions of Zr, ZrCl(4), ZrI(4), and B or Be in sealed Ta tubes for approximately 4 weeks at 850 degrees C. Single-crystal diffraction at room temperature established these as Zr(6)Cl(1.65(4))I(10.35(4))Be and Zr(6)Cl(1.27(3))I(10.73(3))B [R&thremacr;, Z = 3, a = 14.3508(8), 14.389(1) Å, c = 9.8777(9), 9.915(2) Å, respectively] and Zr(6)Cl(11.47(2))I(1.53(2))B [P4(2)/mnm, Z = 2, a = 12.030(1) Å, c = 7.4991(8) Å]. These are derivatives of the Zr(6)I(12)C and orthorhombic Zr(6)Cl(13)B structures, respectively, the latter containing unusual linear chains of clusters interbridged by Cl(i-i) that are in turn interconnected by three-bonded Cl(a-a-a) atoms. The random substitution of fractional Cl at specific I sites in the first two, and I for certain Cl in the third, was positionally resolved in all cases. The replacement always occurs at two-bonded X(i), so that single types of halogen are left in sites that interconnect clusters and generate the three-dimensional array. Structural changes seen in both structures are specifically related to relief of X.X crowding in the parent structure (matrix effects). Substitution of Cl for I(i) in the Zr(6)I(12)C type greatly reduces intercluster I.I repulsions and allows, among other things, a 0.20 Å (5.8%) reduction in Zr-I(a-i) intercluster bond lengths. Increased Cl.I repulsions caused by I substitution in orthorhombic Zr(6)Cl(13)B (Pnnm) convert the twisted chains and angular Cl(a-a-a) interchain bridges to planarity in tetragonal Zr(6)Cl(11.5)I(1.5)B. Phase widths found are 0 </= x </= 1.4 for Zr(6)Cl(x)()I(12)(-)(x)()Z (Z = B, Be) and 0 </= x </= 1.5 for Zr(6)Cl(13)(-)(x)()I(x)()B. The limit for iodine substitution in the chlorine-rich rhombohedral Zr(6)Cl(12)(-)(x)()I(x)()Be is about x = 2.5.

Electric field gradient at the Fe nucleus in ZrFe compounds

In this paper we obtain the electric field gradient at the nucleus (EFG) at the Fe atom in compounds of Zr 2Fe and Zr 3Fe. The results agree well, in magnitude and sign, with experimental values for the EFG inferred from Mössbauer measurements. It is known that Zr 3Fe has an orthorhombic Re 3B-type structure but the distannces and exact coordinates for the Fe site are uncertain. Calculations performed for several positions of the Fe show a very stable value for the EFG, directed along what is usually called the a-axis of the orthorhombic Zr 3Fe structure. We find the asymmetry parameter η to be extremely dependent on the position of the Fe atom. In field Mössbauer measurements for Zr 3Fe indicates that the value of η should be close to zero for this compound. From these measurements and our results we can estimate the position of the Fe site in the orthorhombic structure. The calculations were performed using a recently developed real-space scheme which allows us to obtain the EFG for atoms in metallic alloys. The scheme, based on the recursion method and on the linear muffin-tin orbital (LMTO) formalism in the atomic sphere approximation (ASA), does not involve any adjustable parameters and can be easily applied to non-periodic systems.

Structure and crystallization of amorphous Zr 100−xM x alloys

Amorphous Zr-rich Zr 100-xM x alloys were prepared in the composition range 20≤ x( Fe)≤35, 22≤ x( Co)≤54, 23≤ x( Ni)≤64 for M = Fe, Co, Ni respectively. The structure of the amorphous ZrFe alloys was determined by X-ray diffraction and Mössbauer-effect measurements, which indicate a deviation of the atomic arrangements in these metallic glasses from the DRPHS model. The crystallization processes were investigated by a combined analysis of DSC, resistivity, TEM, X-ray and Mössbauer-effect measurements. In the ZrFe system, crystallization of α-Zr as well as ω-Zr and cubic Zr 2Fe ( a = 12.2 A ̊ ) was observed in the temperature region between 350 and 450° C, followed by a transformation into orthorhombic Zr 3Fe which leads to an additional small exothermal peak in the DSC scan. First results of a comparative analysis of the three systems are discussed.

Local structure of amorphous Zr 3Fe

It is shown that the chemical short-range order (CSRO) of amorphous Zr 3Fe studied by Mössbauer spectroscopy is similar to the CSRO of metastable crystalline Zr 3Fe formed during crystallization while it is quite different from the CSRO of the stable crystalline compounds (ZrFe 2, Zr 2Fe and orthorhombic Zr 3Fe).