Ytterbium carbides

The existence of the ytterbium sesquicarbide with the cubic Pu2C3-type structure was not established (Spedding et al. 1958) under common conditions. However, this type of ytterbium carbide can be prepared at high pressures, like the other high-pressure heavy-lanthanide sesquicarbides (Krupka and Krikorian 1970). 

A common precursor to LnN are the simple inorganic amides Ln(NH2)x (x = 2, 3) which can be placed between the nitrides and the alkyl substituted amides. Their main use lies in the synthesis of other solid materials like lanthanide hydroxides [21,33], carbides [34] or above-mentioned nitrides. Very recently solutions of europium and ytterbium in liquid ammonia have been rediscovered as synthetic tools (Sect. 7.1). 

Here, the so-called heavy lanthanides include the elements from samarium to-lutetium, except for ytterbium and europium which behave like bivalent metals and have unique properties. For these heavy-lanthanide-carbon systems, no complete phase diagram was found, only some information about the formation and the crystal structure of the carbides is available. On the basis of these data the general characteristics of the phase diagrams of the heavy-rare-earth-carbon systems can be summarized. In this case the yttrium-carbon phase diagram may be regarded as the best prototype available for compounds of the heavy lanthanide systems with carbon. 

Many investigators have studied the phase relationship and the formation of the carbides in both the Eu-C and the Yb-C systems, but no complete phase diagram was reported although some data are available on carbides that are formed in the systems. Although europium and ytterbium exhibit variable-valence tendencies, the properties and lattice parameters of their carbides do not follow the systematic variation encountered between the individual lanthanide-carbon system. In addition, an additional new phase, RCs (R = Eu and Yb) forms in the two systems, which is reported to be hexagonal with a Pbj/mmc space group (Guerard and Herold 1975, El-Makrini et al. 1980). 

The YbCo.gj carbide reported by Haschke and Eick (1970a) was not verified to exist in the ytterbium-carbon system by other workers. Its crystal structure was not determined by these authors. In contrast, the two forms of the YCq.s+z compound, the face-centered cubic Fe4N-type form and the rhombohedral CdCl-type form, have been well determined. Their lattice parameters are in good agreement with the systematic variation between those of the other heavy lanthanide hypocarbides, although the composition range for this diphase mixture was not determined. The only information about this material was provided by Spedding et al. (1958). They reported that a carbon-rich YbsC compound exists. 

In comparison with the carbide-forming characteristics of the other heavy-lanthanide-carbon systems, the europium-carbon and ytterbium-carbon systems behave like their neighboring systems. In particular, the types and structures of these carbides are identical. The main difference is the larger lattice parameter of the... 

From these curves the valence state of the rare earth elements, in particular, europium and ytterbium in the carbides can be deduced. It is obvious that europium exhibits the divalent and trivalent states in the tetragonal dicarbide and the cubic hypocarbide, respectively, while ytterbium is only partially divalent (17 at.%... 

The preparative reaction with europium dihydride failed to produce analogous carbide hydrides. Obviously, the failure is consistent with the high stability of divalent europium. In YbCo 5H, YbCHo.s and YbOo.sCo.s, ytterbium is clearly trivalent, as shown by magnetic data (Haschke 1975), and for La and Y the hexagonal phases have also been found (Lallement and Veyssie 1968). Therefore, it can be expected that the hexagonal RCo.sH phases probably exist across the lanthanide series, which exhibit a trivalent state as their stable valence state, with the exception of europium. 

Perchloric acid Phosphomolybdic acid Phosphorus oxychloride Phosphorus pentachloride Phosphorus trichloride y-Picoline Polyphosphoric acid Potassium silicate Rhodium Selenium Selenium dioxide Silica gel Silver oxide (ous) Sodium borohydride Sodium silicate Strontium carbonate Sulfur dioxide Tantalum Tellurium Tetraisopropyl di (dioctylphosphito) titanate Titanocene dichloride Trichloromethylphosphonic acid Tristriphenylphosphine rhodium carbonyl hydride Tungsten carbide Vermiculite Ytterbium oxide Zinc chloride Zinc dust Zinc 2-ethylhexanoate Zirconium potassium hexafluoride... 

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