Uranium compounds, magnetic propertie

Compounds with Sc, Y, lanthanoids and actinoids are of three types. Those with composition ME have the (6-coordinated) NaCl structure, whereas M3E4 (and sometimes M4E3) adopt the body-centred thorium phosphide structure (Th3P4) with 8-coordinated M, and ME2 are like ThAsi in which each Th has 9 As neighbours. Most of these compounds are metallic and those of uranium are magnetically ordered. Full details of the structures and properties of the several hundred other transition metal-Group 15 element compounds fall outside the scope of this treatment, but three particularly important structure types should be mentioned because of their widespread occurrence and relation to other structure types, namely C0AS3,... 

Solid state compounds of uranium have been much studied because of their unusual magnetic properties and their inertness. They are usually made by direct interaction with uranium metal. 

Palstra et al. 1986a, 1987). The temperature dependence of p for UNiSn displays a sharp maximum at 55 K which is followed by a steep decrease of resistivity below this temperature leading to an almost metallic value at 1.6 K. Palstra et al. (1987) claim that the band gap of 0.12 eV is closed at 55 K, which can also lead to the magnetic anomaly at 47 K. Extraordinarily high resistivity values were observed also in isostructural Th and other non-uranium compounds which suggests that this property is not directly connected with the presence of a narrow 5f band at EF. 

Binary compounds can be made with uranium. Such solids state compounds have been investigated because they have interesting magnetic properties. They are made by direct interaction with uranium metal. Oxides mainly form with the general formula UO2, UjOg, UO2. The metal also reacts with other elements such as boron, carbon, nitrogen, phosphorus, and arsenic to make semi-metallic solids. Compounds can also be made using silicon, sulfur, selenium, and tellurium. Urinates can be formed by the addition of uranium with alkali and alkaline Earth metals. 

Paramount information on structure and phase equilibria of the ThMni2 type compounds was collected by Gladyshevsky et al. (1990), while the structure and magnetic properties have been reviewed several times for rare-earth aluminides (Nowik and Felner 1983), rare-earth and actinide aluminides (Suski 1985), actinide aluminides (Sechovsky and Havela 1988), intermetallics with higher content of the iron-group metals for the rare eardis (Buschow 1991, H.-S. Li and Coey 1991), and uranium (Suski 1992). 

Recently, some theoretical works have been published concerning the electronic structure and magnetic properties of the compounds discussed. They concern not only the materials with Y but even with uranium (see e.g. Matar et al. 1994). These preliminary calculations suggest that further progress can be accomplished in this difiScult research area. 

The products were formulated as hexaalkyl dianions, [084]] URi . Although these compounds decompose thermally below room temperature, it proved possible partially to characterize them. Some of the spectroscopic and magnetic properties are rather unusual [2]. In reaction with tetramethylethylenediamine (TMEDA), the Li2UR6-8S complexes yield Li2UR6-7TMEDA derivatives. Sigurdson and Wilkinson [IS] also investigated pentavalent uranium chemistry ... 

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