G. Pedro Smith

Neutron Diffraction and Atomic Distribution in Liquid Lead and Liquid Bismuth at Two Temperatures

Neutron diffraction patterns have been obtained on liquid lead and liquid bismuth at two temperatures. The patterns differ only slightly at the different temperatures, the main peak being slightly shorter and broader and shifted slightly to smaller angles at the higher temperatures. The diffraction patterns have been analyzed to obtain information on the atomic distribution. The first main peak in the distribution curve for liquid lead is at 3.40A and represents about 9.4 atoms. The first main peak in the curve for liquid bismuth is at 3.35A and represents about 7.7 atoms. The second most prominent concentration of atoms occurs at 6.6A for both lead and bismuth.

Temperature Dependence of the Absorption Spectrum of Nickel(II)‐Doped KMgCl3 and the Crystal Structure of KMgCl3

Temperature dependence from 80° to 763°K is reported for the intraconfigurational 3d8↔3d8 transitions of octahedrally coordinated [NiCl6]4− in single crystals of K(Mg1−x, Nix)Cl3 with small x. The crystal structure of the host material, KMgCl3, is reported at 298°, 383°, and 448°K. Band energies are treated in terms of the Liehr—Ballhausen model of d2,8 electronic systems with Dq, B, C, and λ used as empirical parameters. At all temperatures the data are satisfactorily represented by B=850 cm−1, C/B=3.986 (free‐ion value), and λ=−275 cm−1. Thus, B, C, and λ are all reduced to about 82% of their free‐ion values. The parameter λ is estimated from band splittings at 80°K. The parameter Dq varies between −570 cm−1 at 80° and −500 cm−1 at 763°K. Oscillator strengths of the 3A2g→3T1g(F) and 3A2g→3T1g(P) transitions increase by a large factor between 80° and 763°K, while that of 3A2g→3T2g increases by a small factor. The compound KMgCl3 has a cubic perovskite‐type structure at 448°K. At lower temperatures it has...

Vibrational dynamics of glassy and molten ZnCl2

Polarized Raman spectra of ZnCl2 were obtained in the liquid phase near the melting point (T = 598 K), and in the glassy phase (T = 293 K). Measurements were performed down to a very low frequency shift (2 cm−1) from the exciting line. Our analysis of the Raman data provides an interpretation of the collision‐like contribution in terms of a structural relaxation time in the picosecond range, while the phonon‐like contribution gives an effective Raman density of states. These results are also discussed in terms of existing structureal models.

n→π* Electronic Transition in Pure Alkali Nitrate Melts

The lowest‐energy transition (n→π*) of the nitrate ion was found to shift in energy and intensity in a systematic way over the series of molten alkali nitrates from LiNO3 through CsNO3. The energy E of the band maximum varied in a linear way with the cationic radius. At 365°C (extrapolated for CsNO3) E in electron volts was given by (3.81+0.33/r0), where r0 is the cationic radius (Ahrens) in A. The temperature dependence dE/dT was of the order of — 10—4 ev/deg and increased in magnitude with increasing cationic 1/r0. The f number (oscillator strength) decreased steadily along the series of alkali nitrates from 4.1×10—4 for LiNO3 down to 0.86×10—4 for RbNO3 and then rose again to 1.0×10—4 for CsNO3. The thermal coefficient (1/f) (df/dT) was in the range of 10—4 to 10—3 deg—1. The bandwidth changed by only a small amount for changes either in cation or in temperature. The origin of the observed shifts was considered in terms of interionic cohesive forces by application of the Franck‐Condon and conservation ...

Influence of Rare-Gas-Configuration Cations on the Absorption Spectra of Nickel(II) Centers in Liquid Chloride and Bromide Salts

Absorption spectra of dilute Ni2+ centers in melts of CsCl, RbCl, KCl, NaCl, LiCl, MgCl2, CsBr, KBr, and LiBr were measured in the near‐infrared, visible, and, in a few instances, ultraviolet regions. Substantial differences were found in these spectra which correlated with the size of the cations in the solvent salts. The coordination geometry of halides about nickel in CsCl, CsBr, RbCl, KCl, and KBr melts was identified from the spectra as distorted tetrahedral. Coordination geometry in the remaining melts was uncertain. The spectrum for MgCl2 as solvent was very similar to that for LiCl as solvent.

Electronic Spectra and Coordination Geometry in Molten Mixtures of CsCl and NiCl2 Containing up to 60 Mole% NiCl2

Optical absorption spectra (5–26 kK) of fused mixtures of CsCl and NiCl2 containing 2–60 mole % NiCl2 were measured at about 860°C and a mixture containing 20 mole % NiCl2 was studied at 560°—862°C. Up to 20 mole % NiCl2 the Bouguer—Beer law was accurately obeyed, and each nickel was tetrahedrally coordinated to four chlorides. At higher NiCl2 contents, nickel coordination was partitioned between tetrahedral and other (unidentified) geometries. The fraction with tetrahedral coordination progressively decreased with increasing NiCl2 content but was still appreciable at 60 mole % NiCl2. The most prominent feature of the spectrum associated with the unidentified geometries was a band between 18 and 19 kK. These results indicate that nickel has very similar coordination geometries in the liquid and crystalline phases of Cs3NiCl5 but very different coordination geometries in crystalline and liquid CsNiCl3.

Spectroscopic Behavior and Coordination of Nickel(II) in Liquid Mixtures of Zinc and Cesium Chlorides

Optical absorption spectra of dilute solutions of NiCl2 in molten ZnCl2–CsCl mixtures were measured over the complete range of solvent compositions. The temperature extremes investigated were 260°C for melts containing 38 mole % CsCl and 1000°C for 75 mole % CsCl. At temperatures within 100–300°C of the liquidus (depending on melt composition) the spectra were highly composition and temperature dependent and consisted of relatively narrow absorption bands. Analysis of these spectra showed the presence under different conditions of six kinds of nickel(II) centers with well‐defined coordination geometries. An equilibrium between octahedral and tetrahedral centers occurred in 0–8 mole % CsCl such that the octahedral form was favored with increasing CsCl content. A different octahedral–tetrahedral pair occurred in 20–50 mole % CsCl with the tetrahedral form favored by increasing CsCl content and temperature. In CsCl‐rich melts tetrahedrally coordinated Cl3NiClZnCl33− and NiCl42− were found. In ZnCl2‐rich melt...

Electronic Spectra and Coordination of Nickel Centers in Liquid Lithium Chloride—Potassium Chloride Mixtures

The electronic absorption spectra (4–28 kK) of dilute solutions of NiCl2 in liquid LiCl–KCl mixtures were measured at representative solvent compositions and temperatures from pure LiCl to pure KCl and and from 363° to 1070°C. Phenomenologically the spectra respond to changes in temperature at high temperature and changes in solvent composition at low temperatures in ways that are quantitatively very regular. At intermediate temperatures the behavior is more intricate. The data agree well with the following model. Nickel is partitioned between two types of centers, labeled T and O, which are in equilibrium. The T/O concentration ratio increases with increasing temperature and KCl content in the solvent. At low temperatures the fraction of each kind of center varies linearly with the mole fraction of KCl. The O‐center concentration falls below the detection limit at 900°C in all solvents and in KCl at all temperatures. The coordination geometries of these centers are best described as being distributions a...

ABSORPTION SPECTRA OF FUSED-SALT SOLUTIONS

Studies were made of the ultraviolet absorption spectra of the oxy- anions nitrate, chromate, and nitrate in a variety of fused-salt mixtures. (W.L.H.)

Polarized Electronic Absorption Spectrum of Tetragonal NiCl42− Cs3(MgCl4)Cl

The optical absorption spectrum (4000–17 000 A) of crystals of Cs2(Mg0.996Ni0.004Cl4)Cl was measured at approximately 5 and 80°K. The host material was found by x‐ray diffraction to have the Cs3(CoCl4)Cl structure (I4 / mcm) at temperatures down to at least 10°K. In the solid solution the spectra showed that nickel(II) substituted for magnesium, which lies at sites of D2d symmetry with the principal axis aligned with the c axis of the tetragonal crystal. Spectra were measured in both E ⊥ c and E ‖ c polarizations, and the results were in accord with a ligand‐field model having B, C, ξ, B02, B04, and B44 as parameters. Numerous phonon‐creation bands were observed that provided information about excited state potential wells and nuclear motions. In some band systems the individual bands were unusually narrow and well resolved.