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The γ-region of the Mn–Al phase diagram between 45 and 70 at.% Al was re-investigated by a combination of powder and single crystal X-ray diffraction as well as EDS analysis to establish the distribution of Mn and Al atoms. Single crystals of γ-Mn5–xAl8+xwere grown using Sn-flux at 650 °C. The crystal structure, atomic coordinates and site occupancy parameters of γ-Mn5−xAl8+xphases were refined from single crystal X-ray data. The γ-Mn5-xAl8+xphase adopts the rhombohedral Cr5Al8-type structure rather than a cubic γ-brass structure. The refined compositions from two crystals extracted from the Al-rich and Mn-rich sides are, respectively, Mn4.76Al8.24(2)(I)and Mn6.32Al6.68(2)(II). The structure was refined in the acentric R3mspace group (No.160, Z=6), in order to compare with other reported rhombohedral γ-brasses. In addition, according to X-ray powder diffraction analysis, at the Al-rich side the γ-phase coexists with LT–Mn4Al11and, at the Mn-rich side, with a hitherto unknown phase. The refined lattice parameters from powder patterns fall in the range a=12.6814(7)−12.6012(5) Å and c=7.9444(2)−7.9311(2) Å from Al-rich to Mn-rich loadings, and the corresponding rhombohedral angles distorted from a pseudo-cubic cell were found to be 89.1(1)°−88.9(1)°. Magnetic susceptibility and magnetization studies of Mn4.92Al8.08(2)are consistent with moment bearing Mn and suggest a spin glass state below 27 K. Tight-binding electronic structure calculations (LMTO-ASA with LSDA) showed that the calculated Fermi level for γ-“Mn5Al8” falls within a pseudogap of the density of states, a result which is in accordance with a Hume-Rothery stabilization mechanism γ-brass type phases.

To probe the effect of valence electron concentration (vecor e–/atom) on γ‐Pd2+xZn11–xphases a series of compoundsPd2–xAuxZn11(x= 0.3–0.8; e–/atom = 1.70–1.75) was synthesized and structurally characterized. The gold‐substituted γ‐brass type phase was observed for x≤ 0.3, having a refined composition of Pd1.93Au0.27(1)Zn10.80(1)(space group I$\bar{4}$3m; a= 9.0953 (2) Å). Further addition of gold (0.4 ≤ x≤ 0.8) leads to a 2 × 2 × 2 superstructure of theγ‐brass type phase (denoted as the γ′‐phase), with noticeable phase width (F$\bar{4}$3m; 18.1827(4)–18.1799(4) Å). The γ′‐phase consists of four independent 26‐atoms clusters, which are arranged around four distinct high symmetry points. The structural stability and phase width ofγ′‐phase are primarily controlled by two of these clusters, both of which show mixed occupancies and occurrence of non‐stoichiometric vacancies. Amongst all the observed γ′‐phases in the Pd‐Au‐Zn system, the vacancy concentration increases with increasing values of gold substitution. The vecof all observed γ′‐phases fall between 1.636 and 1.654 e–/atom values, which are greatly influenced by the nonstoichiometric vacancies present in the structure.

AbstractThe title compounds Zn13(CrxAl1––x)27(x= 0.34––0.37) were obtained by melting the pure elements at 923 K, and followed by a heat treatment at 723 K in a tantalum container. According to single crystal structural analysis, the title compounds crystallize in the rhombohedral system, adopting a new structure type (R-3m, a= 7.5971(8), c= 36.816(6), for crystal I). Single crystal X-ray structural analysis reveals a statistical mixing of Cr/Al in their crystallographic positions. Single crystal and powder X-ray diffraction as well as energy dispersive X-ray analyses suggested the title phase to have a narrow homogeneity range. The substructure of Zn13(CrxAl1––x)27shows close resemblance with the Mn3Al10structure type. A bonding analysis, through crystal orbital Hamiltonian populations (COHPs), of ““Cr9Al18Zn13”” as a representative composition indicated that both homo- and heteronuclear interactions are important for the stability of this new phase.

Novel ternary phases, (Pd1−xZnx)18(Zn1−yAly)86−δ(0≤x≤0.162, 0.056≤y≤0.088, 0≤δ≤4), which adopt a superstructure of the γ‐brass type (called γ′‐brass), have been synthesized from the elements at 1120 K. Single‐crystal X‐ray structural analysis reveals a phase width (F$\bar 4$3m, a=18.0700(3)–18.1600(2) Å, Pearson symbols cF400–cF416), which is associated with structural disorder based on both vacancies as well as mixed site occupancies. These structures are constructed of four independent 26‐atom γ‐clusters per primitive unit cells and centered at the four special positions A(0, 0, 0), B(1/4, 1/4, 1/4), C(1/2, 1/2, 1/2) and D(3/4, 3/4, 3/4). Two of these, centered at Band C, are completely ordered Pd4Zn22clusters, whereas the other two, centered at Aand D, contain all structural disorder in the system. According to our single‐crystal X‐ray results, Al substitutions are restricted to the A‐ and D‐centered clusters. Moreover, the outer tetrahedron (OT) site of the 26‐atom cluster at Dis completely vacant at the Al‐rich boundary of these phases. Electronic structure calculations, using the tight‐binding linear muffin‐tin orbital atomic‐spheres approximation (TB‐LMTO‐ASA) method, on models of these new, ternary γ′‐brass phases indicate that the observed chemical compositions and atomic distributions lead to the presence of a pseudogap at the Fermi level in the electronic density of states curves, which is consistent with the Hume‐Rothery interpretation of γ‐brasses, in general.

The intermetallic compounds RE10Ni9+xIn20(RE= Ho–Tm, Lu) have been studied experimentally as well as theoretically. Lu10Ni9.8In19.2(1)crystallizes in the tetragonal Ho10Ni9In20‐type structure [space group P4/nmm, a= 13.114(2) Å and c= 8.993(2) Å] with vacant 2bpositions and mixed In/Ni occupancies at one indium site that creates the refined composition. Moreover, the atomic positions and the displacement parameters for the holmium, erbium, thulium, and lutetium phases, which are missing in previous studies, are now refined. TB‐LMTO‐ASA electronic calculations indicates that Lu10Ni9.8In19.2(1)prefers the centrosymmetricHo10Ni9In20‐type rather than a noncentrosymmetricdefect‐HfNiGa2‐type structure (I4mm). According to our theoretical investigations, the HfNiGa2‐type structure is preferred when the 2bposition is fully occupied; however, the Ho10Ni9In20‐type structure is preferred when vacancies are present on 2bposition.

The crystal structure, its variation within the homogeneity range and some physical properties of the new zinc‐rich, partly disordered phase Ir7+7δZn97−11δ(0.31≤δ≤0.58) are reported. The structures of three phases with distinct composition were determined by means of single crystal X‐ray diffraction. Ir7+7δZn97−11δexhibits a significant homogeneity range, adopts a complex γ‐brass related cubic structure (cF403–406), is stable up to 1201(2) K, and transforms sluggishly below 1048(4) K into a phase with 394 atoms in the monoclinic primitive unit cell. It is a diamagnetic, moderate metallic conductor. Six distinguishable clusters consisting of 22–29 atoms comprise the structure. The clusters are situated about the 16 high symmetry points of the cubic Flattice. The structure can be subdivided into two partial structures, one with constant composition IrZn5and 192 atoms per unit cell and a second being significantly richer in zinc with variable composition and 211–214 atoms per unit cell. The meandering triply periodic minimal surface of two interpenetrating diamond‐like nets separates the compositionally variable from its complementary invariant part. The phase width is coupled with substitutional and positional disorder. A comprehensive analysis of composition‐dependent site occupancy factors reveals a linear correlation between the various types of disorder which can be conclusively interpreted in terms of an incoherent intergrowth of distinctive partial structures in variable proportions on a length scale comparable to the size of the approximately 2 nm large unit cell. On the basis of the structural findings we derive the structure chemically meaningful formula Ir7+7δZn97−11δwhich quantitatively accounts for the interrelation between substitutional and positional disorder and provides a measure for the homogeneity range in structural terms.

The decomposition of single or multiple transition metal cupferron complexes in organic solvents under solvothermal conditions and in the presence of long chain amines yields the corresponding oxide nanoparticles. The examples presented here are maghemite γ-Fe₂O₃ nanoparticles from an FeIII–cupferron complex and spinel CoFe₂O₄ nanoparticles starting from CoII–cupferron complex and FeIII–cupferron complex taken in suitable proportions. The nanoparticles are capped with n-octylamine or n-dodecylamine. The presence of amine in the reaction is found to be essential for the formation of the product. The magnetic behavior of pressed pellets of these nanoparticles is presented.

There are a number of pairs of elements A and B in the periodic table that do not form binary oxides A_xB_yO. We have used this fact to seek out crystalline precursors containing such metals that can be decomposed at elevated temperatures to form intimate mixtures of the individual oxides, A_xO and B_yO. Selective leaching of one of these oxide components from the monolithic mixture results in a macroporous material. We demonstrate this scheme by decomposing a hydroxy double salt containing Ni and Zn. The ZnO from the decomposition product can be leached out, leaving behind a macroporous NiO monolith that can be further reduced to yield porous metallic Ni.

The title compounds are characterized by EDS, powder and single crystal XRD, neutron powder diffraction (Cr0.5Fe0.5Ga), magnetic measurements, and TB‐LMTO electronic structure calculations.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

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