Review of Rare-Earth Phosphate Materials for Nuclear Waste Sequestration Applications.

Several materials have or are currently being investigated for nuclear waste sequestration applications, including crystalline ceramic oxides, glasses, and glass-ceramic composites. Rare-earth phosphates have been investigated extensively for this application owing to the range of structures that the hydrous or anhydrous versions can adopt as well as the fact that naturally occurring rare-earth phosphates have been found to contain U or Th. The purpose of this mini-review is to discuss (generally) the properties that must be considered when identifying nuclear wasteform materials and (more specifically) the structure and properties of rare-earth phosphates with special attention being given to the resistance of these materials to radiation-induced structure damage.

Magnetism in Mixed Valence, Defect, Cubic Perovskites: BaIn Fe O, = 0.25, 0.50, and 0.75. Local and Average Structures.

The series BaIn Fe O, = 0.25, 0.50, and 0.

Understanding the Interplay of Vacancy, Cation, and Charge Ordering in the Tunable ScVO Defect Fluorite System.

We report the synthesis, structure, and redox behavior of the cation-ordered tetragonal ScVO defect fluorite superstructure previously thought to be the oxygen precise ABO phase. Four synthesis routes in oxidative, reductive, and inert atmospheres are demonstrated. and powder X-ray and neutron diffraction analyses reveal vanadium disproportionation reactions.

Quenching of Long Range Order and the Mn Ordered Moment in the Layered Antiferromagnet, Ba SrLaMnO. A Polarized Neutron Scattering Study.

SrLaMnO is a layered antiferromagnetic (AF) oxide with the tetragonal ( I4/ mmm) n = 1 Ruddlesden-Popper phase structure (also known as the KNiF structure) with T = 128 K. Remarkably, substitution of Sr by Ba, forming the solid solution BaSr LaMnO, results in the destruction of long-range magnetic order and of the ordered moment on Mn for x > 0.35, although the effective paramagnetic moment remains unchanged, an unprecedented behavior for this class of magnetic materials.

Investigation of Factors That Affect the Oxidation State of Ce in the Garnet-Type Structure.

Oxide materials that adopt the garnet-type structure (XABO) have received attention for a wide variety of applications, one of which is as potential wasteforms for the sequestration of radioactive actinide elements. The actinides are able to be accommodated in the eight-coordinate X site of the garnet structure. This study focuses on the investigation of Ce substitution into the X site as a surrogate for Pu because of their similar chemical properties.

A one-step synthesis of rare-earth phosphate-borosilicate glass composites.

A new 1-step method for synthesizing glass-ceramic composites consisting of rare earth phosphates (REPO) dispersed in borosilicate glass (BG) is reported herein as an alternative to the 2-step approach that is traditionally used. The effect of annealing time and annealing temperature on the formation of the 1-step glass-ceramic composites was investigated. Backscattered electron images and energy dispersive X-ray maps were collected to observe the morphology and chemical distribution in the glass-ceramic composites.

Effect of Synthetic Method and Annealing Temperature on the Structure of Hollandite-Type Oxides.

Hollandite is a class of metal oxide material with the general formula ABO. Several methods have been used in the synthesis of this type of metal oxide, and the synthetic methods reported have typically employed high annealing temperatures between 1200 and 1300 °C. Appropriate synthetic methods must be employed to successfully synthesize these hollandite-type oxides at lower annealing temperatures.

A Structural Investigation of Hydrous and Anhydrous Rare-Earth Phosphates.

Rhabdophane- (REPO·nHO; RE = La to Dy), monazite- (REPO; RE = La to Gd), and xenotime-type (REPO and RE'PO·nHO; RE = Tb to Lu and Y; RE' = Ho to Lu and Y) rare-earth phosphate materials are being considered for a number of applications including as photonic materials, for biolabeling studies, and as potential nuclear wasteforms. Structural studies of hydrous rare-earth phosphates are rather limited when compared to anhydrous rare-earth phosphates. In this study, rhabdophane- (REPO·nHO; RE = La, Nd, Sm, Gd, and Dy) and xenotime-type (REPO·nHO; RE = Y and Yb) materials were synthesized by a precipitation-based method and investigated using X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES).

Investigation of the Thermal Stability of Nd(x)Sc(y)Zr(1-x-y)O(2-δ) Materials Proposed for Inert Matrix Fuel Applications.

Inert matrix fuels (IMF) consist of transuranic elements (i.e., Pu, Am, Np, Cm) embedded in a neutron transparent (inert) matrix and can be used to "burn up" (transmute) these elements in current or Generation IV nuclear reactors.

Investigating the Geochemical Model for Molybdenum Mineralization in the JEB Tailings Management Facility at McClean Lake, Saskatchewan: An X-ray Absorption Spectroscopy Study.

The geochemical model for Mo mineralization in the JEB Tailings Management Facility (JEB TMF), operated by AREVA Resources Canada at McClean Lake, Saskatchewan, was investigated using X-ray Absorption Near-Edge Spectroscopy (XANES), an elemental-specific technique that is sensitive to low elemental concentrations. Twenty five samples collected during the 2013 sampling campaign from various locations and depths in the TMF were analyzed by XANES. Mo K-edge XANES analysis indicated that the tailings consisted primarily of Mo(6+) species: powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3·8H2O), and molybdate adsorbed on ferrihydrite (Fe(OH)3 - MoO4).

Synthesis, structure, and magnetic properties of novel B-site ordered double perovskites, SrLaMReO6 (M = Mg, Mn, Co and Ni).

Four new double perovskites, SrLaMReO(6) (M = Mg, Mn, Co, Ni) in which Re(5+) (5d(2)) is present, were prepared via conventional solid state reactions and characterized by X-ray and neutron powder diffraction, XANES, SQUID magnetometry, and muon spin relaxation (μSR). Synchrotron X-ray and neutron diffraction experiments confirmed that all compounds crystallize in the monoclinic P2(1)/n structure type, which consists of alternately corner-shared octahedra of MO(6) and ReO(6). Rietveld refinement results indicated anti-site mixing of less than 7% on the M/Re sites.

Analysis of the Mo speciation in the JEB tailings management facility at McClean Lake, Saskatchewan.

The JEB Tailings Management Facility (TMF) is central to reducing the environmental impact of the uranium ore processing operation located at the McClean Lake facility and operated by AREVA Resources Canada (AREVA). The geochemical controls of this facility are largely designed around the idea that elements of concern, such as Mo, will be controlled in the very long term through equilibrium with supporting minerals. However, these systems are far from equilibrium when the tailings are first placed in the TMF, and it can take years, decades, or centuries to reach equilibrium.

The effect of synthetic method and annealing temperature on metal site preference in Al(1-x)Ga(x)FeO3.

Magnetoelectric materials couple both magnetic and electronic properties, making them attractive for use in multifunctional devices. The magnetoelectric AFeO3 compounds (Pna2(1); A = Al, Ga) have received attention as the properties of the system depend on composition as well as the synthetic method used. Al(1-x)Ga(x)FeO3.

An X-ray absorption spectroscopic study of the effect of bond covalency on the electronic structure of Gd2Ti(2-x)Sn(x)O7.

The titanate and stannate pyrochlore-type oxides have been investigated because of their potential applications in different fields. Pyrochlore-type oxides exhibit a wide variety of properties such as fast ionic conduction, resistance to radiation induced structural damage, and ferro- and antiferro-magnetism. These properties mainly depend on the metal-oxygen bonding interactions and electronic structure of the materials, both of which can change with composition.

XANES and XPS investigations of the local structure and final-state effects in amorphous metal silicates: (ZrO2)(x)(TiO2)(y)(SiO2)(1-x-y).

Amorphous quaternary [(ZrO(2))(x)(TiO(2))(y)(SiO(2))(1-x-y)] and ternary [(ZrO(2))(x)(SiO(2))(1-x)] silicates were synthesized using a sol-gel method and examined via XPS and XANES. Metal silicates are important industrial materials, though structural characterization is complicated because of their amorphous nature. Hard (Ti K- and Zr K-edge) and soft (Ti L(2,3)-edge) X-ray XANES spectra suggest the Ti and Zr coordination numbers in the quaternary silicates remain constant as the metal identity or total metal content (x, y, or x + y in the chemical formula) is varied.

Local and average structures and magnetic properties of Sr2FeMnO(5+y), y = 0.0, 0.5. Comparisons with Ca2FeMnO5 and the effect of the A-site cation.

Sr(2)FeMnO(5+y) was synthesized under two different conditions, in air and in argon, both of which resulted in a cubic, Pm ̅3m, structure with no long-range ordering of oxygen vacancies. The unit cell constants were found to be a(0) = 3.89328(1) Å for argon (y = 0.

On the oxidation of EuFe4Sb12 and EuRu4Sb12.

Rare-earth-filled transition-metal pnictides having the skutterudite-type structure have been proposed for use as high-temperature thermoelectric materials to recover waste heat from vehicle exhaust, among other applications. A previous investigation by this research group of one of the most studied skutterudites, CeFe(4)Sb(12), found that, when exposed to air, this material oxidized at temperatures that are considerably below the proposed maximum operating temperature. Here, by the combined use of TGA, powder XRD, and XANES, it has been found that the substitution of Ce(3+) and Fe(2+) for larger rare-earth and transition-metal elements (Eu(2+) and Ru(2+)) results in a significantly higher oxidation temperature compared to that of CeFe(4)Sb(12).

Investigation of the Fe K-edge XANES spectra from Fe(1-x)Ga(x)SbO4: local versus nonlocal excitations.

The Fe K-edge X-ray absorption near-edge (XANES) spectra from Fe(1-x)Ga(x)SbO(4), having a rutile-like structure, have been investigated. Similar to the Ti K-edge XANES spectrum from TiO(2) (rutile), the low-energy pre-edge region observed in the Fe K-edge spectra is too broad to be representative of only a local, quadrupolar 1s → 3d excitation. The broadness of this peak results from the presence of a nonlocal transition, referred to as an intersite hybrid, which involves the excitation of 1s electrons to unoccupied 3d states of a next-nearest-neighbor Fe atom.

Examination of the bonding in binary transition-metal monophosphides MP (M = Cr, Mn, Fe, Co) by X-ray photoelectron spectroscopy.

The binary transition-metal monophosphides CrP, MnP, FeP, and CoP have been studied with X-ray photoelectron spectroscopy. The shifts in phosphorus 2p(3/2) core line binding energies relative to that of elemental phosphorus indicated that the degree of ionicity of the metal-phosphorus bond decreases on progressing from CrP to CoP. The metal 2p(3/2) core line binding energies differ only slightly and show similar line shapes to those of the elemental metals, reaffirming the notion that these transition-metal phosphides have considerable metallic character.