J.P. Young

Transformation of monoclinic californium bromide to orthorhombic CfBr3 by the application of pressure

A new synthetic route to the orthorhombic form of CfBr/sub 3/ is reported. A few micrograms of monoclinic CfBr/sub 3/ is loaded and studied in a triangular-shaped diamond anvil pressure cell similar to that reported by Merrill and Bassett. Based on analysis of the absorption spectra obtained from the CfBr/sub 3/ sample at several pressures up to 3.4 GPa, it is concluded that the structural transformation of monoclinic CfBr/sub 3/ to orthorhombic CfBr/sub 3/ takes place between 1.7 and 3.4 GPa. 10 references, 1 figure.

A diamond anvil cell for absorption spectral studies of actinides to 30 GPa

Abstract A diamond anvil cell has been constructed for use in conjunction with a microscope-spectrophotometer for obtaining room-temperature absorption spectral data from actinide samples at pressures of up to at least 30 GPa. Tests have demonstrated that the pressure cell is safely compatible with the microgram-sized, radioactive, and air-sensitive actinide samples of interest. Presented here are the details of the cell design, its preparation for sample loading, sample loading, application of pressure, and adaptation of the spectrophotometer. The results of several performance tests are summarized also to indicate the type and quality of data obtainable with the pressure cell.

The effect of pressure on the absorption spectrum and the crystal structure of anhydrous AmI3

Anhydrous AmI3 was investigated as a function of pressure up to approximately 10 GPa in a diamond anvil cell using absorption spectrophotometric analysis. AmI3 is the only actinide tri-iodide known presently to be dimorphic, and at room temperature and normal pressure there is an appreciable difference between the molecular volumes of each structure. It has been determined that an applied pressure of approximately 2 GPa will convert the rhombohedral form (large molecular volume) of AmI3 to the orthorhombic structure. this structural change with pressure has been interpreted as reflecting relative packing efficiencies in the crystals. This is believed to be the first spectrophotometric observation of a pressure induced phase transition in an actinide compound.

Studies of selected transuranium and lanthanide tri-iodides under pressure using absorption spectrophotometry☆

Abstract The anhydrous tri-iodides of plutonium, americium and curium under pressure have been investigated using absorption spectrophotometry. These initial studies on plutonium and curium tri-iodides together with the published data for americium tri-iodide show that the rhombohedral form of these compounds (BiI3-type structure) can be converted to the orthorhombic form (PuBr3-type structure) by applying pressure at room temperature. Absorption spectrophotometry can often differentiate between two crystallographic forms of a material and has been used in the present high-pressure studies to monitor the effects of pressure on the tri-iodides. A complication in these studies of the tri-iodides is a significant shift of their absorption edges with pressure from the near UV to the visible spectral region. With curium tri-iodide this shift causes interference with the major f-f absorption peaks and precludes identification by absorption spectrophotometry of the high pressure phase of CmI3.

Absorption spectrophotometric study of berkelium(III) and (IV) fluorides in the solid state

Abstract Absorption spectrophotometry has been used to study the dimorphic BkF3 system and BkF4 in the solid state. LaF3-type trigonal BkF3 can be distinguished from YF3-type orthorhombic BkF3 by subtle, but reproducible, differences in their corresponding absorption spectra. This ability emphasizes the sensitivity of absorption spectrophotometric analysis, since both crystal modifications of BkF3 have the same metal ion coordination number of nine. The absorption spectrum of BkF4 (UF4-type monoclinic structure) is reported for the first time.

High temperature spectroscopic and X-ray diffraction studies of californium tribromide: Proof of thermal reduction to californium(II)

Abstract Californium tribromide (CfBr 3 ) has been studied on the several microgram scale by spectroscopic and X-ray powder diffraction methods between 25°C and about 700°C. Spectroscopic evidence indicates that CfBr 3 undergoes reduction to produce Cf(II) in greater amounts with increasing temperature, with about 15–30 per cent reduction at 600°C. Despite the ingrowth of Cf(II) into the CfBr 3 with increasing temperature, all the powder diffraction patterns exhibited only the monoclinic AlCl 3 -type structure characteristic of CfBr 3 confirming this structure type as the high-temperature one. A mechanism involving a reversible shift of electron density from the Br ions to the Cf(III) ions with temperature is postulated to explain satisfactorily the experimental observations made in the present and previous studies. Californium triiodide is predicted to undergo thermal reduction to Cf(II) more readily than CfBr 3 .

Absorption spectrophotometric and X-ray diffraction studies of the trihalides of promethium in the solid state

Abstract The anhydrous trihalides of promethium (Z = 61) were examined by absorption spectrophotometry and X-ray powder diffraction. Room temperature lattice parameters for PmF3, PmCl3 and PmBr3 were in agreement with those obtained by Weigel and Scherer. Two previously unreported crystallographic modifications of PmI3 were found. The low temperature, PuBr3-type orthorhombic form of PmI3 had lattice parameters a 0 = 4.24(1) A , b 0 = 13.93(7) A and c 0 = 9.96(2) A , and those for the high temperature, BiI3-type rhombohedral form (based on the corresponding hexagonal cell) were a 0 = 7.65(3) A and c 0 = 21.10(10) A . Each compound has been characterized on the basis of its solid state absorption spectrum, in addition to characterization by X-ray powder diffraction analysis.

Absorption spectrophotometric studies of some lanthanide and actinide halides under pressure

Abstract Diamond anvil cells have been used for absorption spectrophotometric studies of lanthanide and actinide halides over a pressure range of 10 −4 to > 30 GPa. Irreversible spectral changes with pressure in AmI 3 and CfBr 3 have previously been correlated with structural transformations to a more dense form of both compounds. Reversible spectral changes with pressure are more difficult to interpret. In NdCl 3 the spectral changes as pressure is increased suggest the formation of a phase of higher symmetry. With compression of AmCl 3 , the spectral changes observed are more subtle. CfCl 3 retains its hexagonal structure at pressures up to 22 GPa. Other studies of Cf(III) chlorides have indicated the formation of a new compound, as yet unidentified, whose spectra as a function of pressure also exhibit reversible changes. Complementary X-ray diffraction data, presently lacking, would help elucidate these phenomena.

Spectral studies of O2−, NO2− and CrO42− in molten LiF-NaF-KF and of O2− in liquid ammonia

Abstract Spectral studies of O2−, CrO42− and NO2− in molten LiF-NaF-KF at 500°C and of O2− in liquid ammonia were carried out. O2− ion exhibits a single absorption peak at 254 nm. It is, however, unstable in molten LiF-NaF-KF. In the same solvent CrO42∮- exhibits two bands at 372 and 265 nm; the molar absorptivity of the two bands are 3970 and 2940 M−1 cm−1, respectively, at 500°C. In the same molten salt solvent, NO2− exhibits a single absorption band at 365 nm. In liquid ammonia, O2− exhibits an adsorption peak at 252 nm with a molar absorptivity of approximately 3000 M−1 cm−1 at −33°C. A method for the removal of chromium ions and certain other reducible ions from molten LiF-NaF-KF is also presented.

Absorption spectrophotometric study of CfCl3 at pressures up to 35 GPa

Abstract Diamond anvil cells have been used for absorption spectrophotometric studies of both PuBr, -type, orthorhombic and UCl3-type, hexagonal CfCl3 as a function of pressure, up to 35 GPa. It was observed that the latter crystallographic form of CfCl3 irreversibly transformed to that of the former on the application of pressure between 22 and 30 GPa. A discussion of the spectral changes that are observed as a function of the applied pressure is given along with a description of possible mechanisms by which the phase transformation can occur.