Karl A. Gschneidner

Systematics of the intra-rare-earth binary alloy systems

Abstract A generalized phase diagram for the trivalent intra-lanthanide and yttrium-lanthanide binary alloys is proposed. This single diagram represents a total of 91 phase diagrams. A method of calculating unknown diagrams is described. These 91 diagrams can be classified into 13 types of phase diagrams, examples of 11 types are known, and a hypothetical diagram is calculated for the other two types. The lattice spacings of these intra-rare-earth alloys generally exhibit positive deviations from Vegards law if the end-members have the same structure. This is consistent with the second-order elasticity model explaining deviations from Vegards law. Both positive and negative deviations are found in the light lanthanide -heavy lanthanide alloys where the end-members always have different structures. These behaviors are explained on the basis of the d occupation number which decreases from the light lanthanides to the heavy lanthanides.

Chapter 262 – R5T4 Compounds: An Extraordinary Versatile Model System for the Solid State Science

Abstract Rare earth metals form intermetallic compounds with most of the metallic and semimetallic elements in the periodic table. Due to chemical similarities among 16 of the 17 rare earth elements (Sc frequently stands apart), they often form families of either isostructural or closely related compounds. Despite a long history of research in a broad field of intermetallics, a general theory that enables one to clearly relate composition and structure with physical properties of a multicomponent alloy is still lacking. In this chapter, we review a family of intermetallic materials formed by the rare earth metals (R) and Group 14 elements (T, which can also include certain quantities of Group 13 and 15 elements substituted for Group 14 elements) at the R5T4 stoichiometry. The uniqueness of these compounds lies in their distinctly layered crystallography that can be judiciously controlled by chemistry, processing, and a variety of external triggers including temperature, pressure, and magnetic field. The materials exhibit a host of physical effects related to magnetic and structural transformations that can occur separately or simultaneously. Unlike many other extended families of intermetallic materials, present day understanding of the composition–structure–physical property relationships of R5T4 compounds approaches predictive power, and in this chapter, we show examples of how one can predict some of the interesting physics based on the knowledge of chemical composition and crystal structure of these materials. We hope that this review will further stimulate research in this area and that the science of these materials will be refined and extended in the coming years making the subject much more complete.

Chapter 4 Cerium

Publisher Summary The chapter discusses Cerium, which in its elemental form is the most fascinating member of the periodic table. Cerium, under various conditions of temperature and pressure, is an antiferromagnet, a superconductor, and the only pure element to exhibit Kondo scattering and a solid–solid critical point. These phenomena occur because the energy of the inner 4f level is nearly the same as that of the outer or valence 5d and 6s levels, and thus only small amounts of energy are necessary to change the relative occupancy of these electronic levels giving rise to a variable electronic structure. There are five established allotropic forms of cerium and some evidence for two or three others, which actually may be metastable, or impurity stabilized. The pressure–temperature relationships of the stable phases, their crystal structures, and valences are discussed first under equilibrium conditions. Then non-equilibrium and hysteresis effects relative to the five established phases are reviewed. The known information on the less reliably established phases is examined.

High field low temperature heat capacity of CePd3B0.3

Heat capacity of CePd3B0.3 in the temperature range 1.5 to 20 K in zero and applied magnetic fields up to 10 T has been measured. CT develops a maximum in applied fields which shifts to higher temperatures as the field is increased. In conjunction with the results reported earlier in the literature, the present experiment indicates competing Kondo and Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange interactions with TK ≈ TRKKY.

SOME COMMENTS ON THE YTTERBIUM-THORIUM SYSTEM

Experimental observations showing that ytterbium and thorium exhibit very limited mutual solid and liquid miscibilities are shown to be in complete accord with prediction. Although ytterbium has an atomic size about 8% larger than thorium, and the electronegativity difference between the two elements is only 0.37 units, it has been shown that it is the simultaneous, not the individual, application of these two factors which is important in determining the extent of solid solubility. A plot given for thorium and ytterbium metals shows that thorium lies just outside the outer ellipse for ytterbium and that ytterbium lies beyond thc outer ellipse for thorium. Therefore, very limited solid solubilities of thorium in ytterbium and vice versa are predicted. (P.C.H.)

Chapter 282 – Systematics

Altogether, the rare earths represent the largest fraction (about 1/6) of naturally occurring elements. Over the last 60 years many of the rare earth elements have become indispensable for modern technology, and the family as a whole has become a poster child for demonstrating the vital role in analysis of systematics and anomalies plays in science. Indeed, a systematic analysis of trends in structure and properties of materials moving from one member of the rare earth family to another has often resulted in correct predictions that later have been verified theoretically, experimentally, or both. To this end, this chapter briefly reviews some examples of development and successful applications of systematics that brought about a great deal of understanding of the fundamentals of chemistry, physics, and materials science of rare earths and their compounds and alloys.

The lower critical field of U6Fe

The magnetization curves of U6Fe were measured at several constant temperatures by a SQUID magnetometer. The lower critical field Hc1 was determined on the basis of Beans model. Hc1 follows a 1−(T/TC)4 dependence and its extrapolated value at T=0 is 92 Gauss. Hc1 is three orders of magnitude smaller than Hc2.