Lanthanide crystals

As was the case with lanthanide crystal spectra (25), we found that a systematic analysis could be developed by examining differences, AP, between experimentally-established actinide parameter values and those computed using Hartree-Fock methods with the inclusion of relativistic corrections (24), as illustrated in Table IV for An3+. Crystal-field effects were approximated based on selected published results. By forming tabulations similar to Table IV for 2+, 4+, 5+ and 6+ spectra, to the extent that any experimental data were available to test the predictions, we found that the AP-values for Pu3+ provided a good starting point for approximating the structure of plutonium spectra in other valence states. However,... 

Abstract Amino acids are the basic building blocks in the chemistry of life. This chapter describes the controllable assembly, structures and properties of lathanide(III)-transition metal-amino acid clusters developed recently by our group. The effects on the assembly of several factors of influence, such as presence of a secondary ligand, lanthanides, crystallization conditions, the ratio of metal ions to amino acids, and transition metal ions have been expounded. The dynamic balance of metalloligands and the substitution of weak coordination bonds account for the occurrence of diverse structures in this series of compounds. 

Newman, D.J., 1971. Theory of lanthanide crystal fields. Adv. Phys. 20, 197. 

Brief history of lanthanide crystal field theory. 575... 

Structure and metal radii. Most of the trivalent lanthanide metals display a close packed structure at room temperature. The light lanthanides crystallize in a dhep, the heavier lanthanides in a hep form. The high temperature form is, in general,... 

A comparison of the distance dependence of F2 and 4f obtained from host lattice and high pressure studies is included in Figs. 4 and 5. We see from the figures that the distance dependence obtained from the pressure study is more pronounced. Shen and Holzapfel attributed the difference in distance dependence to pressure-induced distortions in the local coordination environment of Sm +. We consider local distortions in more detail below in our discussion of lanthanide crystal field parameters. 

The crystal-field interaction in lanthanide-ion spectra in solids is weak in the sense that perturbations that shift the positions of the free-ion levels are small (compared to corresponding shifts in transition-metal spectra) and the effects of coupling different free-ion levels by the crystal field are small. The weakness of the lanthanide crystal-field interaction is a consequence of the shielding of the 4r configuration by the outer 5s and 5p atomic shells and is reflected in the historical sequence of theoretical advances in lanthanide crystal-field theory. 

It is important to stress once more that pSR measures the fluctuations of the localflelds at the muon site and not directly the fluctuations of the spins creating those fields. This means in essence that for a quantitative analysis (for TF as well as for ZF measurements) the exact relations between the individual components of lanthanide spin correlations S t)SfQ)) and the muon field correlations B t)B jS)) must be worked out for each particular muon spin -> lanthanide crystal geometry. This step is often overlooked. The general tensorial relation between spin and field correlation has been given by Dalmas de Reotier et al. (1996). 

Dysprosium (Dy) has electronic configuration of [Xe] 6s 5d 4f . The complete trivalent lanthanide crystal stmcture sequence can also be accessed in Dy with the application of pressure. Dysprosium has been extensively studied to various pressure ranges (Patterson et al., 2004 Samudrala and Vohra, 2012 Shen et al., 2007). 

The structural phase transitions in thulium have been studied to 195 GPa (Montgomery et al., 2011). The lanthanide crystal structure sequence, hep Sm-type dhep dfee, is observed below 70 GPa. It is to be noted that the pure/cc phase is not seen in this study. The hexagonal hR24 phase (Montgomery et al., 2011) and orthorhombic Cmmm (Pravica et al., 2006) are used... 

Luminescence of lanthanides in crystalline form is maybe the best-known application for the common people. The lighting and display industry has utilized the unique long lifetime luminescence as phosphors and laser industry has exploited lanthanide crystals since population inversion is easy to achieve with Iruig lifetime laser materials. Beyond the luminescence use, lanthanides are used in magnets, glass production, as colorants, contrast agents, in computer memories - the... 

The lanthanide ion-ligand interaction undergoes changes at thermal excitations of a crystal as well. When the temperature rises, the population of the excited sublevels produces anomalies in the thermal expansion of crystals. Redistribution of electron density in a lanthanide crystal results in significant changes in the vibrational spectrum of a lattice, when variations in temperature occur. This is particularly evident for the anomalous temperature behaviour of elastic constants. 

Besides the JT effect some other interesting cooperative phenomena take place in concentrated lanthanide crystals. Thus Battison et al. (1975) have observed the splitting of an excited doublet of Ho + ion in die non-diluted compound H0VO4 witiiout lowering of the crystal symmetry. This phenommon is described as Davydov splitting due to magnetic dipole-dipole and phonon-field-mediated interaction of the Ho ions (Aminov 1981). 

In analysis of the physical properties of lanthanide crystals the superposition model (Bradbury and Newman 1968, Newman 1971) is widespread. In this model a) the crystal field is formed only by the nearest neighbours (ligands) of an R ion b) the interaction of the 4f electron with a ligand is axially symmetric, so the Hamiltonian of an ion in the field of the v-th ligand is written as follows (the quantization axis is directed along the radius-vector Ry of the ligand, the origin placed on the R ion) ... 

Elastic constants of lanthanide crystals with zircon and scheelite structure (in GPa)... 

The rapid rise of the hep-Sm-type phase boundary beyond Tm (fig. 123), and the anomalous high pressures of transformation in Y (hep - Sm-type, Sm-type dhep and dhep - fee) relative to lanthanide elements was cited by Gschneidner (1985b) as evidence for 4f valence electron hybridization having a significant role in determining the lanthanide crystal structure. He noted, however, that d occupation number probably is more important in determining which crystal structure would form, as had been proposed by others (e.g., see Duthie and Pettifor, 1977 Skriver, 1983). 

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