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Growth and Preparation of Quasicrystalline Samples

Title: "Intergrowth compounds in the Zn-Rich Zn-Pd system: Toward 1D quasicrystal approximants"

Authors: O. Gourdon and G.J. Miller

Contact:  G.J. Miller

Journal:  Chem. Mater. (2006) 18, 1848-1856.

Abstract:

A series of γ-brass related structures in the Zn-rich portion of the Zn-Pd phase diagram (ca. 80 at % Zn) is investigated using single-crystal diffraction and tight-binding electronic-structure calculations. Earlier research identified regular arrays of inversion antiphase domains (IAPDs) over a narrow composition range but did not report any characteristic superstructure(s) over the same range. Single-crystal X-ray diffraction allowed for the identification of lattice constants for six "phases" in Zn1-xPdx (0.15 < x < 0.25), and refinements of two crystal structures indicate two important potential building blocks for the intermediate compositions, one of these being the cubic g-brass structure. A Farey tree construction is described that accounts for the observed long-period superlattice and provides a possible algorithm for targeting one-dimensional, quasiperiodic phases in this and related systems. Tight-binding electronic-structure calculations on the two limiting structures for this region of the Zn-Pd phase diagram suggest a relationship between structure and bonding in these complex intermetallic systems.

Title: "Exploratory synthesis of reduced rare-earth-metal halides, chalcogenides, intermetallics"

Authors: J.D. Corbett

Contact:  J.D. Corbett

Journal:  J. Alloys Compd. (2006) 418, 1-20.

Abstract:

A new direction in reduced rare-earth-metal (R) compounds opened up when tantalum (and niobium) were adapted to use as virtually faultless containers for these reactions, as these gave immediate access to many new metal-rich phases and structures. Examples are summarized for the new binary dihalides (e.g., Pr, Nd, Dy, Ho, Tm), metallic diodides (Sc, La, Ce, Gd), and metal-metal bonded chains (Sc, Y, Gd, Lu) that were so discovered. Furthermore, a large array of condensed metal cluster, chain, and sheet halides arise when a stoichiometric amount of a diverse variety of nonmetal or metal atoms is included to serve as an interstitial, the earliest examples originating with traces of common impurities. A change in anion charge type to telluride affords a whole new regime of condensed metal-rich cluster compounds and structures, including such remarkable examples as (Sc, Gd, Dy)2Te, Lu11Te4, Lu8Te, and Sc6PdTe2. Also, a number of novel Zintl phases, interstitial derivatives of the type R5Ge3Z, quasicrystals, and their approximants are generated in other intermetallic systems. Generalities in structures and bonding are described along the way.

Title: "Zn1-xPdx (x=0.14-0.24): A missing link between intergrowth compounds and quasicrystal approximants"

Authors: O. Gourdon, Z. Izaola, L. Elcoro, V. Petricek, and G.J. Miller

Contact:  G.J. Miller

Journal:  Philos. Mag. (2006) 86, 419-425.

Abstract:

Our investigations in the Zn-rich portion of the Zn-Pd system are related to the idea that a prototypic 1-dimensional (1D) quasicrystal, as defined by the Fibonacci sequence, can be regarded both as a quasicrystal and as an incommensurately modulated crystal. Consequently, there are two different ways to achieve the atomic structure. Six different new structures, closely related to the γ-brass structure, in the Zn1-xPdx system have been synthesized and contain Pd-centered Zn icosahedra. A misfit character of all structures with two distinct main subsets and satellite reflections is clear from the diffraction patterns. Among these six structures, two specific examples, Zn10.65Pd2.35 (Zn0.819Pd0.181) and Zn212Pd64 (Zn0.768Pd0.232), have been refined by single crystal X-ray diffraction using traditional refinement methods but also using the (3+1)D formalism (superspace group Xmmm(00γ)0s0). Analogies with the Fibonacci sequence are possible if we identify dimers of Pd-centered Zn icosahedra (DI) as short segments, S, and trimers of Pd-centered Zn icosahedra (TI) as long segments, L. By defining these S and L segments, Zn11Pd2 and Zn212Pd64 correspond to the two first simplest approximants of a hypothetical 1D quasicrystal.

Title: "Tuning icosahedral quasicrystals and their approximants from the Mg2Zn11 structure"

Authors: Q. Lin and J.D. Corbett

Contact:  J.D. Corbett

Journal:  Philos. Mag. (2006) 86, 607-613.

Abstract:

Electronic tuning of Sc-Mg-Zn icosahedral quasicrystal (i-QC) and approximant (AC) phases was achieved according to pseudogap predictions from an electronic band structure analysis of Mg2Zn11. The i-QC and two AC phases were obtained in the Mg2-xScxZn11 system. The QC compositions are Sc10.8(6)Mg3.2(6)Zn86.0(2) and Sc14.6(4)Mg3.3(4)Zn82.1(2) by EDX for x=1.0 and 1.5, respectively X-ray structure determination reveals that the 1/1 AC, Sc3Mg0.18(1)Zn17.73(1), crystallizes in space group Im3, with a=13.863(2) Å. Electronic structure calculations on the 1/1 AC reveal that the Fermi level is located in the center of the pseudogap, which appears to be greatly enhanced by Zn 4p and Sc 3d orbital mixing.

Title: "Quasicrystal formation in gas-atomized Zr80Pt20 powders"

Authors: X.Y. Yang, E.A. Rozhkova, and D.J. Sordelet

Contact:  X.Y. Yang

Journal:  Philos. Mag. (2006) 86, 309-315.

Abstract:

Gas-atomized powders with a nominal composition of Zr80Pt20 have been investigated as a function of powder size range. Atomized powders were screened to the following sizes for examination:  <10 μm; +10, -20μm; +20, -45μm; +45, -75μm; +75, -106μm. For comparison of as-synthesized structure and crystallization behavior, Zr80Pt20 melt-spun ribbons (MSRs) were also prepared. Results show that during atomization a metastable quasicrystalline (QC) phase is formed as the predominant phase independent of powder size; a small volume of amorphous phase and crystals were detected in finer and coarser sized powders, respectively. The QC grains formed during atomization are much larger than the nanosized quasicrystal obtained in the MSR, which is most likely attributed to the much slower cooling rates during gas atomization. Nucleation and growth occur during both rapid solidification routes. The formation of an icosahedral quasicrystal during gas atomization and melt spinning is consistent with previous suggestions that icosahedral local structure exists in liquids and amorphous phases and facilitates nucleation of quasicrystal formation in Zr80Pt20 alloys.

Title: "Stability of icosahedral Cd-Yb at low temperature"

Authors: G. Krauss, W. Steurer, A.R. Ross, and T.A. Lograsso

Contact:  G. Krauss

Journal:  Philos. Mag. (2006) 86, 505-516.

Abstract:

The stability of i-Cd-Yb was studied between ambient temperature and 90 K using single-crystal diffraction. To study the influence of mechanical stress at low temperatures, a modified grinding-jar housing was constructed and ball-milling experiments were carried out at 77 K. In neither case structural changes were observed.  This indicates the thermodynamic stability of this binary quasicrystal.

Title: "Synthesis and characterization of hexagonal Cd51Yb14 single crystals"

Authors: D. Wu, O. Ugurlu, L.S. Chumbley, M J. Kramer, and T.A. Lograsso

Contact:  D. Wu

Journal:  Philos. Mag. (2006) 86, 381-387.

Abstract:

Synthesis of large, bulk single grains of the hexagonal crystalline phase Cd51Yb14 has been accomplished using the Bridgman method. Growth was carried out under controlled solidification conditions in sealed Ta crucibles, which maintain compositional integrity by eliminating evaporative losses of Cd and reaction with the containment material. Compositional analysis of the as-grown phase indicates no evidence of macrosegregation along the length of the crystal. High-resolution transmission electron microscopy (TEM) characterization of the hexagonal phase is hampered by the enhanced atmospheric reactivity of the higher Yb content of the hexagonal phase. Such a high sensitivity to ambient exposure was not observed during the recent synthesis and TEM studies of the quasicrystalline Cd5.7Yb or cubic approximate phase Cd6Yb. TEM and X-ray transmission diffraction results taken at the Advanced Photon Source at Argonne National Laboratory show the presence of a fine-structured second phase, which is randomly oriented throughout the matrix. The precipitates have been identified as pure Cd by d-spacing comparisons and likely form by selective atmospheric oxidation of Yb from the Cd51Yb14 phase.

Title: "Cluster-based composition rule for stable ternary quasicrystals in Al-(Cu, Pd, Ni)-TM systems"

Authors: C. Dong, J.B. Qiang, Y.M. Wang, N. Jiang, J. Wu, and P. Thiel

Contact:  C. Dong

Journal:  Philos. Mag. (2006) 86, 263-274.

Abstract:

Although hundreds of quasicrystals have been found, little is known about their quantitative composition rules that can help design new materials. In this paper we propose a cluster-based approach to decipher the composition rules. Our approach consists of the following steps: (1) selection of a known basic cluster in the constituent binary systems; (2) construction of a cluster line linking the binary cluster composition to a third element; and (3) the intersection of the two cluster lines points to a new quasicrystal composition if the e/a ratio falls in the appropriate range, typically from 1.8 to 2.0. The predicted compositions agree satisfactorily with experimental values.

Title: "Linkage between oxygen content and metastable phase formation in melt spun Zr80Pt20 alloys"

Authors: D. Sordelet and X. Yang

Contact:  D. Sordelet              

Journal:  Transactions of the Indian Institute of Metals (2005) 58, 749-760.

Abstract:

This report continues previous studies that show melt spun Zr80Pt20 ribbons having oxygen contents ranging from <200 to approximately 5000 mass ppm form various metastable phases during quenching. In the presence of sufficient oxygen, a big cube Zr6Pt30 phase forms, but this structure is destabilized towards an icosahedral quasicrystalline structure at lower oxygen levels. Further reduction of oxygen promotes increasingly stable Zr-Pt bonds, and a metastable b-Zr(Pt) structure is formed.

Title: "Quasicrystals in the Ti-Zr-Ni alloy system"

Authors: J.B. Qiang, Y.M. Wang, D.H. Wang, M. Kramer, P. Thiel, and C. Dong

Contact: P. Thiel

Journal: J. Non-Cryst. Solids (2004) 334-335, 223-227.

Abstract:
The empirical compositional criteria for ternary quasicrystals (QCs) based on the QCs' phase diagram features are applied in the Ti-Zr-Ni alloy system. The ideal quasicrystals-forming composition. Ti40Zr40Ni20 has been identified, which lies at the crossing point of the two specific lines, termed as e/a-constant and e/a-variant lines. Bulk quasicrystalline Ti/Zr-based alloys are obtained in region of (TixZr100-x)100-yNiy (43.75 ≤ x ≤ 81.25, yr = 17, 20 in at.%) by copper mold casting. It was confirmed that Ti40Zr40Ni20 is the optimal QC-forming composition, where a nearly pure bulk quasicrystal rod, 6 mm in diameter, can be formed. With a small deviation from this ideal composition, the Ti(Zr) solid solution phases and/or C14-type Laves phase, though as minority phases, are found coexisting with the majority icosahedral phase. At the same time, the explanation of the e/a-variant line is explored.

Title: "Growth and physical properties of the decagonal Al-Cu-Co quasicrystal grown from the ternary melt"

Authors: R.A. Ribeiro, S.L. Bud'ko, F.C. Laabs, M.J. Kramer, and P.C. Canfield

Contact: P.C. Canfield

Journal: Philos. Mag. (2004) 84, 1291-1302.

Abstract:
Large faceted single-grain quasicrystals of the approximate composition Al63.2Cu19.5Co17.3 and with a high degree of structural perfection are obtained through the slow cooling of a ternary melt with initial composition Al65Cu29Co6. X-ray diffraction patterns of crushed single-grain samples are exceptionally sharp, indicating a high degree of structural order, with no evidence of secondary phases. Transmission electron micrographs also reveal sharp diffraction patterns in the even-n layers but diffuse scattering in the odd-n layers. Temperature-dependent magnetization, electrical resistivity and specific heat are measured using bars cut perpendicular and parallel to the c axis and show diamagnetic behaviour: γ ≈ 0.5 mJ mol-1 K-2, ρc(2 K) ≈ 52 μΩ cm and ρq(2 K) ≈ 283 μΩ cm.

Title: "Bridgman-grown i-Al68.9Pd21.6Mn9.5 quasicrystal: Comparison of α , CP, σ, and χ with those for flux-grow samples"

Authors: C.A. Swenson, T.A. Lograsso, N.E. Anderson, Jr., and A.R. Ross

Contact: T.A. Lograsso

Journal: Phys. Rev. B (2004) 70, 094201/1-094201/11.

Abstract:
Thermal expansivity (α, 1–300 K), heat capacity (CP, 1–108 K), electrical conductivity (σ, 1–300 K) and magnetic susceptibility (χ, 1–300 K) data have been obtained for a Bridgman-grown single grain i-Al68.9Pd21.6Mn9.5 quasicrystal (BR) for direct comparison with data previously published for a flux-grown single grain sample [Phys. Rev. B 65, 184206 (2002); PRB], and present σ, χ and CP data for a second flux-grown sample described in an earlier publication [Philos. Mag. B 79, 1673 (1999); PM]. Fortuitously, comparative analyses show these samples to have essentially the same composition. At all temperatures, σ and χ for BR are, respectively, approximately one-third and one-quarter those for PRB. The CP's are the same (±1%) down to 30 K, below which the BR CP decreases more rapidly to one-half that for PRB at 1 K. The α's agree to ±2% from 300 to 40 K, with a more rapid decrease for BR below 30 K, eventually to 0.6 αPRB below 4 K. The total Grüneisen parameters are similar at all temperatures. The two methods for sample growth differ primarily in a quenching of the flux-grown sample to room temperature after growth, while the Bridgman-grown sample cools very slowly, resulting in slightly different phases, and magnetic properties which are associated with lattice defects. An attempt to convert the single grain flux-grown sample to the phase of the Bridgman sample using an 800°C anneal and a slow cool to room temperature was not successful, with the appearance of second phase inclusions. These inclusions are ascribed to slightly different compositions for the two phases [see Boissieu et al., Philos. Mag. A 78, 305 (1998)]. This suggests that a single grain flux-grown sample with an Mn composition near 9% cannot be converted by annealing and slow cooling into a single grain LT phase, and vice versa. These considerations may not apply to samples with Mn compositions closer to 8%.

Title: "The stability of icosahedral Cd-Yb"

Authors: G. Krauss, S. Deloudi, A. Steiner, W. Steurer, A.R. Ross, and T.A. Lograsso

Contact: T.A. Lograsso

Journal: Mater. Res. Soc. Symp. Proc. (2004) 805, 41-46.

Abstract:
The stability of single-crystalline icosahedral Cd-Yb was investigated using X-ray diffraction methods in the temperature range 20 K ≤ T ≤ 900 K at ambient pressure and from ambient temperature to 873 K at about 9 GPa. Single-crystals remain stable at low temperatures and in the investigated HP-HT-regime. At high temperatures and ambient pressure, the quasicrystal decomposes. The application of mechanical stress at low temperatures yields to the same decomposition, the formation of Cd. A reaction of icosahedral Cd-Yb with traces of oxygen or water causing the decomposition seems reasonable, but a low-temperature instability of this binary quasicrystal cannot be ruled out totally.

Title: "New stable icosahedral quasicrystalline phase in the Sc-Cu-Zn system"

Authors: Q. Lin and J.D. Corbett

Contact: J.D. Corbett

Journal: Philos. Mag. Lett. (2003) 83, 755-762.

Abstract:
Stable icosahedral quasicrystals have been synthesized in the Sc-Cu-Zn system by quench-and-anneal or in-situ filtration methods. These have a composition near Sc16.2(3)Cu12.3(3)Zn71.5(6) at 480 °C with a quasilattice const. of 4.995 6(7) Å determined by the Elser method from a single-phase Guinier pattern. An electron diffraction study confirms that the icosahedral quasicrystals have a primitive lattice. Cuboctahedral single crystals with dimensions up to 100 μm have been grown by melt-spinning techniques. A cubic approximant phase Sc14.2Cu10.3Zn75.5 (ScCu0.73Zn5.33) with a concordant lattice constant lies nearby.

Title: "Ti-Zr-Ni bulk quasicrystals prepared by casting"

Authors: J. Qiang, Y. Wang, D. Wang, M. Kramer, and C. Dong

Contact: M. Kramer

Journal: Philos. Mag. Lett. (2003) 83, 467-472.

Abstract:
A broad bulk-quasicrystal-forming region, (TixZr100-x)100-yNiy (43.75 ≤ x ≤ 81.25, 17 ≤ y ≤ 23), has been identified in the Ti-Zr-Ni system, and quasicrystals can be obtained by using a conventional suction-casting method. The quasilattice constant of the icosahedral (i) phase is within the range 0.505-0.530 nm. Ti40Zr40Ni20 is the optimal composition, where nearly pure bulk quasicrystals can be obtained. With a slight deviation from this composition, Ti-Zr solid-solution phases and/or C14-type Laves phase, although minority phases, coexist with the majority i phase. Differential thermal analysis reveals that the i phase in the bulk as-cast Ti40Zr40Ni20 alloy is stable below 953 K and transforms to the C14-type Laves phase and β-Ti-Zr solid solution at higher temperatures.

Title: "Formation of quasicrystals in Zr-Pd-(Cu) melt spun ribbons and mechanically milled powders"

Authors: D.J. Sordelet, E. Rozhkova, M.F. Besser, and M.J. Kramer

Contact: D.J. Sordelet

Journal: Intermetallics (2002) 10, 1233-1240.

Abstract:

Amorphous Zr70Pd30 and Zr70Pd20Cu10 alloys were prepared by mechanical milling and melt spinnng to compare their devitrification behaviors. The devitrification of mechanically milled Zr70Pd30 and Zr70Pd20Cu10 powders occurs via a single-step, first-order transformation to a stable Zr2Pd tetragonal structure. This is in sharp contrast to the devitrification of the same amorphous alloys prepared by melt spinning, in which a primary meta-stable quasicrystalline phase forms. Since the mechanical milling process does not involve direct liquid phase formation of an amorphous structure, it is inferred that the short-range order in the solid state derived amorphous powder is different from that in the melt spun ribbon. During mechanical milling of an amorphous melt spun ribbon, crystallization of the quasicrystalline phase appears to precede disordering into an amorphous structure having an different short range order. Deformation of an amorphous melt spun ribbon by repetitive rolling at ambient temperatures crystallizes the meta-stable quasicrystalline phase.

Title: "Synthesis route-dependent formation of quasicrystals in Zr70Pd30 and Zr70Pd20Cu10 amorphous alloys"

Authors: D.J. Sordelet, E. Rozhkova, M.F. Besser, and M.J. Kramer

Contact: D.J. Sordelet

Journal: Appl. Phys. Lett. (2002) 80, 4735-4737.

Abstract:

The devitrification of mechanically milled amorphous Zr70Pd30 and Zr70Pd20Cu10 powders occurs via a single-step, first-order transformation to a stable Zr2Pd tetragonal structure. This is in sharp contrast to the devitrification of the same amorphous alloys prepared by melt spinning, in which a primary metastable quasicrystalline phase forms. Since the mechanical milling process does not involve direct liquid phase formation of an amorphous structure, it is inferred that the short-range order in the solid state derived amorphous powder is different from that in the melt spun ribbon.

Title: "High-temperature solution growth of intermetallic single crystals and quasicrystals"

Authors: P.C. Canfield and I.R. Fisher

Contact: P.C. Canfield

Journal: J. Cryst. Growth (2001) 225, 155-161.

Abstract:

Solution growth continues to be one of the most powerful techniques for the production of single crystals for basic and applied research. It is a versatile technique that allows for the growth of congruently and incongruently melting materials with equal ease. The primary requirement for growth is that there be an exposed primary solidification surface in the appropriate equilibrium alloy phase diagram. In this paper, we will review some of the systems that we have applied this technique to over the past several years. These range from binary and ternary intermetallic compounds such as RFe2 (R=Rare earth) and RT2Ge2 (T=Ni and Cu) to the refractory RNi2B2C family of magnetic superconductors to several families of quasicrystals. In each case, specific nuances of the relatively simple growth technique will be discussed.

Title: "The influence of growth rate on porosity in Al-Pd-Mn icosahedral quasicrystals"

Authors: A.R. Ross, I.R. Fisher, P.C. Canfield, and T.A. Lograsso

Contact: T.A. Lograsso

Journal: Mater. Res. Soc. Symp. Proc. (2000) 643, K1.5.1-K1.5.5.

Abstract:

Growth experiments have been carried out to characterize the occurrence and development of porosity in Bridgman and flux grown Al-Pd-Mn icosahedral quasicrystals. The porosity level has been observed to fluctuate between values of 0.0 and 3.75 percent along the length of Bridgman single crystals implying that the development of porosity is affected by the local growth conditions. Experiments were conducted to evaluate the influence of the rate of solidification on the occurrence of porosity. Alloys were solidified with different growth rates, 1mm/hr and >10 mm/hr, using the Bridgman configuration and at different cooling rates, ranging from 0.29°C/hr to 10°C/hr, using the flux growth method. Porosity levels were analyzed via optical image analysis. These experiments indicate that porosity percentages are greatly influenced by cooling rates and crystal size.

Title: "Growth of large single-grain quasicrystals from high temperature metallic solutions"

Authors: I.R. Fisher, M.J. Kramer, Z. Islan, T.A. Wiener, A. Kracher, A.R. Ross, T.A. Lograsso, A.I. Goldman, and P.C. Canfield

Contact: T.A. Lograsso

Journal: Mater. Sci. Eng., A (2000) 294-296, 10-16.

Abstract:

Flux-growth techniques have been successfully applied to the preparation of several families of quasicrystals and related approximant phases. Large (up to 1 cm3) single-grain samples have been obtained for icosahedral R–Mg–Zn (R=Y, Gd, Tb, Dy, Ho and Er), decagonal Al–Ni–Co, icosahedral Al–Pd–Mn, icosahedral Al–Ga–Pd–Mn, and the ξ′ Al–Pd–Mn approximant phase. The samples are obtained by slowly cooling ternary (or quaternary) melts of a composition that intersects the primary solidification surface of the desired phase in the equilibrium ternary alloy phase diagram (i.e. this is a self-flux technique). The technique clearly reveals the growth habit, and results in remarkably strain-free quasicrystals.

Title: "Formation and morpholgoical development of porosity in icosahedral Al-Pd-Mn alloys"

Authors: A.R. Ross, T.A. Wiener, I.R. Fisher, P.C. Canfield, and T.A. Lograsso

Contact: T.A. Lograsso

Journal: Mater. Sci. Eng., A (2000) 294-296, 53-56.

Abstract:

Directional solidification and quenching experiments have been conducted to examine the formation and origin of the faceted porosity commonly observed in icosahedral Al–Pd–Mn alloys. Faceted porosity has been previously observed in both Czochralski grown and Bridgman grown single crystals during single-phase solidification of the icosahedral phase. Detailed observations in Bridgman grown single crystals indicate that the distribution and quantity of pores are non-uniformly distributed along the length of the as-grown ingot. This non-uniform distribution suggests that their formation is influenced by both chemical segregation during solidification as well as convection in the liquid. Controlled solidification of this alloy followed by quenching of the solid–liquid interface provides for a time–temperature history of the porosity formation and morphological development as a function of processing conditions.

Title: "On the growth of decagonal Al-Ni-Co quasicrystals from the ternary melt"

Authors: I.R. Fisher, M.J. Kramer, Z. Islam, A.R. Ross, A. Kracher, T. Wiener, M.J. Sailer, A.I. Goldman, and P.C. Canfield

Contact: M.J. Kramer

Journal: Philos. Mag. B (1999) 79, 425-434.

Abstract:

High-quality, single grain samples of decagonal Al-Ni-Co quasicrystals with volumes of up to 0.8 cm3 and an approximate composition of Al72Ni11Co17 have been grown from the ternary melt. The precise growth methods and conditions are discussed in detail. X-ray diffraction patterns of crushed single grains and of single-grain samples are exceptionally sharp indicating a high degree of structural order with no eivdence of second phases. Transmission electron micrographs also reveal sharp diffraction patterns in the even n layers but diffuse scattering in the odd n layers, indicative of a structure intermediate between the Al73Co27 and Al69Ni31 end members. The electrical resitivity measured diretly from cut bars for currents flowing perpendicular to the crystalline direction (i.e. perpendicular to the c axis) is non-metallic, with a broad maximum around 180K, and a value of approximately 310 µW cm at 300K. The resistivity for currents flowing parallel to the c axis is metallic and is almost an order of magnitude smaller in value than for i perpendicular to c..

Title: "On the growth of icosahedral Al-Pd-Mn quasicrystals from the ternary melt"

Authors: I.R. Fisher, M.J. Kramer, T.A. Wiener, Z. Islam, A.R. Ross, T.A. Lograsso, A. Kracher, A.I. Goldman, and P.C. Canfield

Contact: M.J. Kramer

Journal: Philos. Mag. B (1999) 79, 1673-1684.

Abstract:

Icosahedral Al71Pd21Mn8 quasicrystals have been grown from the ternary melt via a "self-flux" technique. The nucleation is exceptionally well controlled, and individual grains can have masses of up to almost 30 g (limited only by the dimensions of the growth crucible). The quasicrystals grown by this technique are readily separated from the melt by decanting, and clearly manifest a dodecahedral morphology with pentagonal facets. X-ray and electron diffraction data indicate a remarkably well-ordered structure, with a correlation length of over 1000 Å. The magnetic susceptibility has a temperature-independent diamagnetic component, and a temperature-dependent paramagnetic term. For temperatures greater than approximately 60 K, the paramagnetic term follows a Curie-Weiss temperature dependence characterized by an average effective moment of 0.62 ± 0.02 μB/Mn, and a Weiss temperature of -12.8 ± 0.1 K. Deviations from the Curie-Weiss temperature dependence for temperatures less than approximately 60 K may be due to the formation of local (short range) magnetic correlations. The electrical resistivity has a broad maximum at approximately 90 K, and a room temperature value of 1.57 ± 0.05 mΩcm. We note that the previously observed empirical trend that a very high resistivity is associated with the highest quality Al-Pd-Mn quasicrystals does not seem to be in general true, and that these high-quality (as demonstrated by x-ray and electron diffraction) "flux-grown" samples, have a relatively low room temperature resistivity. In addition to the ternary icosahedral Al-Pd-Mn quasicrystals, a novel pseudo-quaternary icosahedral quasicrystal, Al67Ga4Pd21Mn8, is described in the appendix to this paper.

Title: "Processing of Al-Cu-Fe quasicrystalline single grains"

Authors: T.A. Lograsso and A.R. Ross

Contact: T.A. Lograsso

Journal: Mater. Res. Soc. Symp. Proc. (1999) 553, 3-12.

Abstract:

The phase equilibrium of the Al-Cu-Fe quasicrystalline phase (ψ phase) is complex and conventional crystal growth techniques like the Bridgman and Czochralski methods are not applicable in preparation of large crystals. Large single grains of the ψ phase been have prepared by either slow cooling or isothermal anneals. In the later technique, arc melted ingots were subjected to either single or multiple heat treatments between 825 and 840°C to encourage grain growth. Following heat treatment, grains of the icosahedral phase are found either as isolated pentagonal-faceted crystals within the ingot or within clusters of intergrown grains. The growth of the large grains is independent of the sample processing history of the sample, is facilitated by the presence of liquid at the growth temperatures and is constrained by the physical dimension of the ingot. The microstructure of both grain types is similar contg. a minor quantity (on the order of 5-10%) of a second phase and a high degree of porosity in the as-grown state. The second phase is usually present as a thin layer between adjacent grains or associated with a pore within a single grain. The grain porosity is distributed throughout the ingot. These defects can be removed through post-growth hot isostatic pressing and anneal treatments.

Title: "Growth of large-grain R-Mg-Zn quasicrystals from the ternary melt (R=Y, Er, Ho, Dy, Tb)"

Authors: I.R. Fisher, Z. Islam, A.F. Panchula, K.O. Cheon, M.J. Kramer, P.C. Canfield, and A.I. Goldman

Contact: M.J. Kramer

Journal: Philos. Mag. B (1998) 77, 1601-1615.

Abstract:

The growth of large (up to 0.5 cm3), single-grain R-Mg-Zn quasicrystals (R = Y, Er, Ho, Dy, Tb) from a ternary melt is described in detail. The quasicrystals grown by this technique have a composition R8.7Mg34.6Zn56.8, are thermodynamically stable, and have a dodecahedral morphology with clearly visible pentagonal facets. The quasicrystalline phase has been examined by x-ray diffraction, high resolution transmission electron microscopy, elemental analysis and transport measurements. In addition, results are presented for a closely related ternary crystalline phase.

Title: "Preparation of well-defined samples of AlPdMn quasicrystals for surface studies"

Authors: C.J. Jenks, D.W. Delaney, T.E. Bloomer, S.-L. Chang, T.A. Lograsso, Z. Shen, C.-M. Zhang, and P.A. Thiel

Contact: C.J. Jenks

Journal: Appl. Surf. Sci. (1996) 103, 485-493.

Abstract:

We have developed a method for preparing single-grain, quasicrystalline AlPdMn samples for surface studies in ultrahigh vacuum. The main issues of concern are phase purity, the quality of the surface structure, and the surface composition. Phase purity is enhanced by annealing the sample in ultra-pure Ar in a sealed quartz ampoule for several days before polishing. Polishing with colloidal silica allows secondary phases to be detected readily with an optical microscope. As a final precaution, phase purity can be checked sensitively with scanning Auger microscopy. After this stage, the sample can be cleaned in ultrahigh vacuum with ion bombardment. Annealing is required after bombardment to restore surface structure and to obtain a low-energy electron diffraction (LEED) pattern of an oriented sample. However, both ion bombardment, and heating to temperatures above 870 K in vacuum, produce Pd-rich surfaces. As a final step, for the five-fold surface, we recommend heating briefly to 1050-1100 K and then annealing at 870 K for several hours. This produces both an excellent LEED pattern, and a surface composition close to that of the bulk.

Title: "Suppression of secondary phases during growth of icosahedral Al70Pd21.5Mn8.5 single grains"

Authors: D.W. Delaney, T.E. Bloomer, and T.A. Lograsso

Contact: T.A. Lograsso

New Horizons in Quasicrystals: Research and Applications Conference Proceedings, Ed. A. I. Goldman, D. J. Sordelet, and J. M. Dubois, World Scientific, Singapore, 45-52 (1997).

Abstract:

Large, highly perfect single grains of the icosahedral Al-Pd-Mn phase can be prepared by the Bridgman technique. These single grains are typically harvested from a multi-grained ingot with the yield of high quality single grains limited by second phases and porosity found along the length of the ingot. These defects arise from compositional changes resulting from the normal course of solidification of an alloy with complex phase equilibria coupled with segregation driven by convective flows. This study examined the microstructural development during crystal growth and characterizes the chemical segregation found along the length of an ingot. By adjusting the initial composition of the alloy, the yield, quality and size of single-phase icosahedral grains have been increased.

Title: "Determination of the liquidus surface in the quasicrystalline region of the Al-Cu-Ru system"

Authors: T.A. Lograsso and S.A. Haines

Contact: T.A. Lograsso

Journal: J. Non-Cryst. Solids (1996) 197, 197-204.

Abstract:

The liquidus surface and primary phase regions surrounding the quasicrystalline region of the Al-Cu-Ru system have been studied to determine if a composition exists which will produce single crystals using conventional crystal growth techniques, e.g., Bridgman or Czochralski techniques. The solidification sequences and microstructural evolution were examined for a wide range of compositions using differential thermal analysis, powder x-ray diffraction, energy dispersive spectroscopy and standard optical microscopy. Several ternary solidification reactions were identified and a liquidus surface has been proposed. It was determined that the alloys of quasicrystalline composition solidify incongruently through a series of peritectic reactions.

Title: "Preparation of large single grains of the quasicrystalline icosahedral Al-Cu-Fe ψ phase"

Authors: T.A. Lograsso and D.W. Delaney

Contact: T.A. Lograsso

Journal: J. Mater. Res. (1996) 11(9), 2125-2127.

Abstract:

A cyclic heat treatment process was used to prepare single grains of the quasicrystalline icosahedral phase, ψ-Al65Cu23Fe12. Alloys of appropriate composition are melted and chill cast into copper molds. Multiple cyclic heat treatments at successively higher temperatures below 860 °C, the peritectic decomposition temperature of the quasicrystal phase, are used to enhance the growth of the ψ phase. Single grains up to 10 mm x 5 mm x 5mm have been prepared.

Title: "Dynamics of the AlMnPd icosahedral phase"

Authors: M. deBoissieu, M. Boudard, R. Bellissent, M. Quilichini, B. Hennion, R. Currat, A.I. Goldman, and C. Janot

Contact: A.I. Goldman

Journal: J. Phys.: Condens. Matter (1993) 5, 4945-4966.

Abstract:

A centimetre-sized single grain of the perfect AlPdMn icosahedral phase was grown by slow cooling from the melt. It has been fully characterized to be of perfect icosahedral symmetry, i.e. without any frozen-in phason strain. The dynamical properties of this icosahedral phase have been studied by means of inelastic neutron scattering measurements on a triple-axis spectrometer. The response function S(Q, omega ) was measured around several Bragg reflections and along the high-symmetry twofold, threefold and fivefold axes of the icosahedron. In the long-wavelength limit there are well defined phonons whose width is limited by the instrumental resolution. The isotropy of acoustic modes is verified and the corresponding sound velocities are in good agreement with ultrasonic measurements made on the same sample. At shorter wavelengths, gaps are expected. By analogy with 1D models and electron density of states calculations, the positions in reciprocal space where the strongest gaps are expected may be estimated. This defines a set of three main pseudo-Brillouin zones which are quasiperiodically stacked around each strong Bragg reflection chosen as the zone centre. In the limit of the instrumental resolution no gap could be detected, even when two branches crossed.

Title: "Dynamical x-ray diffraction from an icosahedral quasicrystal"

Authors: S.W. Kycia, A.I. Goldman, T.A. Lograsso, D.W. Delaney, D. Black, M. Sutton, E.Dufresne, R. Bruning, and B. Rodricks

Contact: A.I. Goldman

Journal: Phys. Rev. B (1993) 48, 3544-3547.

Abstract:

We present direct evidence of dynamical diffraction of x rays from a quasicrystal. High-resolution x-ray-diffraction measurements of the Al-Pd-Mn face-centered icosahedral quasicrystal were performed, revealing a mosaic full width at half maximum of less than 0.001°. In a second experiment, the anomalous transmission of x rays (the Borrmann effect) was observed. These measurements show that nearly perfect quasicrystals may be grown to centimeter-size dimensions allowing x-ray techniques based upon dynamical diffraction to be brought to bear on the analysis of icosahedral structures.


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