Structural relationships, crystal chemistry and anion substitution processes for M(III)X3 systems of the lanthanides and actinides

An examination of data for lanthanide and actinide phases with UCl3-type and PuBr3-type M(III)X3 structures has shown that these systems are conveniently described by alternating layers of [MX2]n+n and [X]n-n. The relationships between the UCl3- and PuBr3-type structures are described and expanded to include a variety of anion substitution systems, M(III)X3-xYx. The two different types of [MX2]n+n layers observed in these systems are consistent with the existence of a novel structural unit, [M2X4]2+. The effects of radius ratio constraints and layering mechanisms on the phase equilibria and anionic substitution processes, polymorphism and crystal growth in the MX3-xYx systems are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22030/1/0000448.pd

Structural correlations of the lanthanide halides and related compounds. Derivatives of the anti-nickel-arsenide structure

An examination of structural data for lanthanide halides and related compounds has shown that a substantial number of different structure types are conveniently described as layered structures derived from anti-NiAs by removal or shear of cation layers and distortion of the residual layers. The structural correlations of various MX, MX1.5, MX2, MXY, MX3, and MX2Y compositions (M = cation, X and Y = anions) are described by the presentation of a subgroup-supergroup diagram relating their space groups and by comparison of their structural projections. A close relationship between the CsCl- and NiAs-type structures is observed. The occurrence of displacive and order-disorder phase transitions, the formation ternary derivatives by ion accommodation processes and the possible formation of intermediate halides, M2X2n+1, by coherent intergrowth of MX2 and MX3 structures are discussed. The effects of radius ratio and cation coordination number on the stabilities of halide structures and on the formation of complex MX2 layers derived from hexagonal-closest-packed metal arrays are examined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21736/1/0000129.pd

The lanthanum hydroxide fluoride carbonate system: The preparation of synthetic bastnaesite

Hydrothermal phase equilibria in the lanthanum + hydroxide + fluoride + carbonate system have been investigated along an isobaric and isothermal section of variable metal to fluoride ratio, x. Quantitative substitution of fluoride into LaOHCO3 proceeds with the formation of a continuous solid solution, La(OH)1-xFxCO3, for 0 0 [les] x [les] 1 and a two-phase region, LaFCO3 + LaF3, for 1 x 3 is an orthorhombic phase (a = 21.891(5), B = 12.639(3) and C = 10.047(2) A) which is not isostructural with LaFCO3. Hydrolysis of the La(OH)1-xFxCO3 phase to the corresponding UCl3-type La(OH)3-xFx compositions has been observed. Thermal decomposition reactions of the hydroxide fluoride carbonates are described, and a geochemical process for the formation of bastnaesite and tysonite is proposed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22168/1/0000599.pd

The phase equilibria, vaporization behavior, and thermodynamic properties of europium tribromide

Europium tribromide has been found to vaporize incongruently according to the reaction:2EuBr3(s)=2EuBr2(s)+Br2(g).Static equilibrium vapor pressures have been measured by a spectrophotometric procedure in the temperature range 502 to 623 K. Equilibrium pressures were not attained in Knudsen effusion experiments. For the vaporization reaction, ΔHo(563 K)/kcalth mol-1 = (22.85 ± 0.18) and ΔSo(563 K)/calth K-1 mol-1 = (34.26 ± 0.32). Heat capacities have been estimated for the condensed bromides, and second- and third-law results are given. For the tribromide, ΔHof(EuBr3, s, 298.15 K)/kcalth mol-1 = -(186.1 ± 3.0), ΔGof(EuBr3, s, 298.15 K)/kcalth mol-1 = -(179.3 ± 3.0) and So(EuBr3, s, 298.15 K)/calth K-1 mol-1 = (50.7 ± 3.0). The preparative chemistry and phase equilibria of the europium + bromine system and the thermochemical data are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33930/1/0000197.pd

Quantum Calogero-Moser Models: Integrability for all Root Systems

The issues related to the integrability of quantum Calogero-Moser models based on any root systems are addressed. For the models with degenerate potentials, i.e. the rational with/without the harmonic confining force, the hyperbolic and the trigonometric, we demonstrate the following for all the root systems: (i) Construction of a complete set of quantum conserved quantities in terms of a total sum of the Lax matrix (L), i.e. (\sum_{\mu,\nu\in{\cal R}}(L^n)_{\mu\nu}), in which ({\cal R}) is a representation space of the Coxeter group. (ii) Proof of Liouville integrability. (iii) Triangularity of the quantum Hamiltonian and the entire discrete spectrum. Generalised Jack polynomials are defined for all root systems as unique eigenfunctions of the Hamiltonian. (iv) Equivalence of the Lax operator and the Dunkl operator. (v) Algebraic construction of all excited states in terms of creation operators. These are mainly generalisations of the results known for the models based on the (A) series, i.e. (su(N)) type, root systems.Comment: 45 pages, LaTeX2e, no figure

Exactly solvable potentials of Calogero type for q-deformed Coxeter groups

We establish that by parameterizing the configuration space of a one-dimensional quantum system by polynomial invariants of q-deformed Coxeter groups it is possible to construct exactly solvable models of Calogero type. We adopt the previously introduced notion of solvability which consists of relating the Hamiltonian to finite dimensional representation spaces of a Lie algebra. We present explicitly the $G_2^q$-case for which we construct the potentials by means of suitable gauge transformations.Comment: 22 pages Late

Vaporization and thermodynamic properties of samarium dicarbide and sub-stoichiometric disamarium tricarbide

The vaporization reactions of SmC2(s) and Pu2C3-type SmCy(s, 1.36 y SmC2(s) = 2C(s)+Sm(g){2/(2-y)}SmCy(s) = {y/(2-y)}SmC2(s)+Sm(g)The complex reaction for SmCy occurs because the composition of the carbon-rich boundary of the phase decreases as temperature increases. For reaction (i), the equiliblium pressure is described by log10{(p/po)(Sm, g, 1548 K T T/K)-1. The non-linear pressure equation for reaction (ii) is log10{(p/po)(Sm, g, 1.42 y T T/K)-1 + 7018500(T/K)-2 +/- 0.038}. Thermodynamic values for the vaporization and formation reactions of SmC2(s) and SmCy(s) at 298.15 K have been calculated: [Delta]Hto(SmC2, s, 298.15 K) = -(96.2 +/- 7.5) kJ [middle dot] mol-1 and [Delta]Hfo(SmC1.43, s, 298.15 K) = -(89.0 +/- 8.0) kJ [middle dot] mol-1. The thermodynamic results are discussed and compared with values reported for other lanthanide carbides.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24147/1/0000404.pd

Preparation, phase equilibria, and crystal chemistry of lanthanum, praseodymium, and neodymium hydroxide chlorides

The preparation of hydroxide chlorides of lanthanum, praseodymium, and neodymium has been achieved by hydrothermal methods at 550[deg]C and 1530 atm. Three phases (Ln(OH)3, Ln(OH)2.55Cl0.45, and Ln(OH)2Cl) have been characterized by analytical and X-ray methods. The observed compositions are closely defined by the x = 0, 0.5, and 1 members of the homologous anion substitution series, Ln(OH)3-xClx. The previously unreported Ln(OH)2.55Cl0.45 phases are clearly substoichiometric in chloride and are described by the Ln7(OH)18Cl3 composition. X-ray diffraction data for the phases at x = 0.45 show a pronounced UCl3-type substructure and complex superstructure reflections that have been indexed on a hexagonal cell. For the lanthanum phase, a = 17.662 (6) and c = 3.914(1) A. Efforts to obtain single crystals have been unsuccessful. Thermal decomposition processes of the hydroxide chlorides have been investigated, and the characterization of LaO(OH)0.55Cl0.45, a monoclinic YOOH-type intermediate phase, is reported. Structural features and phase equilibria of the hydroxide chlorides are discussed and analogies with the hydroxide nitrate systems are drawn.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21828/1/0000231.pd

Aluminium metallisation for interdigitated back contact silicon heterojunction solar cells

Back contact silicon heterojunction solar cells with an efficiency of 22 were manufactured, featuring a simple aluminium metallisation directly on the doped amorphous silicon films. Both the open circuit voltage and the fill factor heavily depend on the parameters of the annealing step after aluminium layer deposition. Using numerical device simulations and in accordance with the literature, we demonstrate that the changes in solar cell parameters with annealing can be explained by the formation of an aluminium silicide layer at temperatures as low as 150 C, improving the contact resistance and thus enhancing the fill factor. Further annealing at higher temperatures initialises the crystallisation of the amorphous silicon layers, yielding even lower contact resistances, but also introduces more defects, diminishing the open circuit voltag

Star Formation History in two fields of the Small Magellanic Cloud Bar

The Bar is the most productive region of the Small Magellanic Cloud in terms of star formation but also the least studied one. In this paper we investigate the star formation history of two fields located in the SW and in the NE portion of the Bar using two independent and well tested procedures applied to the color-magnitude diagrams of their stellar populations resolved by means of deep HST photometry. We find that the Bar experienced a negligible star formation activity in the first few Gyr, followed by a dramatic enhancement from 6 to 4 Gyr ago and a nearly constant activity since then. The two examined fields differ both in the rate of star formation and in the ratio of recent over past activity, but share the very low level of initial activity and its sudden increase around 5 Gyr ago. The striking similarity between the timing of the enhancement and the timing of the major episode in the Large Magellanic Cloud is suggestive of a close encounter triggering star formation.Comment: 30 pages, 22 figures, accepted for publication in Ap