Rare earth nitride carbide

Rare earth cyanide compounds can be obtained by a reaction between the corresponding metal and cyanic acid in liquid ammonia, but when rare earth metals react with cyanic acid directly under ambient conditions the related cyanide compounds can not be obtained, but the products will be rare earth nitride and carbide. 

In the so-called interstitial nitrides the metal atoms are approximately, or in some cases exactly, close-packed (as in ScN, YN, TiN, ZrN, VN, and the rare-earth nitrides with the NaCl structure), but the arrangement of metal atoms in these compounds is generally nor the same as in the pure metal (see Table 29.13, p. 1054), Since these interstitial nitrides have much in common with carbides, and to a smaller extent with borides, both as regards physical properties and structure, it is convenient to deal with all these compounds in Chapter 29. 

Some examples within this group are rare-earth nitrides I90]. silicon nitride [191] or molibdenum nitride and carbide j 192. 193). 

This chapter briefly reviews what is known of the rare earth borides, carbides, and nitrides. This review wonld particularly like to showcase interesting features of the crystal structure and intriguing physical properties ranging ft-om the fundamental to the very applicable, with an emphasis on recent emerging results in important functionalities such as magnetism, thermoelectricity, and superconductivity. 

While there are myriad helpful reviews, there has previously been no up-to-date, one-stop review article available for any one of the rare earth borides, carbides, and nitrides, and in this sense I feel tiiis chapter, which contains brief summaries, valuable references as gateways to further detailed information, and a focus on timely topics of all three systems, will be particularly useful. A section is included at the end summarizing the particularly notable physical properties described in each section. 

I would like to briefly sum up some of the notable physical properties of the rare earth borides, carbides, and nitrides described in the previous sections. 

To suimnarize, the rare earth borides, carbides, and nitrides have yielded interesting compounds with striking features in their crystal structures and physical properties, and also successfiil applications. They also appear to be systems that are amenable to materials design. This is an important direction to strive for in the current world where natural resources are limited, namely, to highly functionalize materials that are mainly composed of abundant light elements through the innovative use of a small amount of rare element. 

Binary rare-earth compounds such as carbides, sulfides, nitrides, and hydrides have been used to prepare anhydrous trihalides, but they offer no special advantage. Treating these compounds at a high temperature with a halogen (98) or hydrogen halide (115) produces the trihalide, e.g.,... 

Gschneidner, K, A, Jr, Kippenhan, N, "Thermochemistry of the Rare Earth Carbides, Nitrides and Sulfides for Steelraaking", IS-RIC-5 Rare Earth Information Center, Iowa State Univ., Ames, lA, 1971. 

Paramagnetism results from unpaired electrons. As a result, most compounds containing transition, rare-earth, and actinide elements, including oxides, nitrides, carbides, and borides, exhibit paramagnetism. Such ceramics are generally not of importance due to their paramagnetism alone, since they often exhibit other types of magnetism, as well. 

Ashcroft, N.W., 1968, Phys. Rev. Lett. 21,1748. Baggio-Saitovitch, E.M., D.R. Sanchez and H. Mick-litz, 2001, in Rare Earth Transition Metal Boro-carbides (Nitrides) Superconducting, Magnetic and Normal State Properties, eds K.-H. Mailer and... 

Free energies of formation of rare earth compounds are in the order oxides > oxysulphides > sulphides > nitrides > carbides. Thermodynamically, the addition of rare earths in steel-making should favour deoxidation and desulphurization. 

A further group of ternary nitrides are of the type R2Fei7Nx where R is a rare earth element such as Sm, Ce or Nd, and x indicates the variable nitrogen content. These phases have been prepared, by nitridation at relatively low temperatures and up to 15 MPa N2, under which conditions the nitrogen content can reach x = 3. They are closely related to borides and carbides with the similar formula and have attracted considerable... 

Altounian, Z., Chan, X., Liao, L. X., Ryan, D. H. Strom-Olsen, J. O. (1993). Structure and magnetic properties of rare earth iron nitrides, carbides and carbonitrides. Journal of Applied Physics, 73, 6017-22. 

McColm et al. (1977) considered that the eomposition ranges seem to be related to the amounts of R(IV) found in the respective nitrides and carbides (Lorrenzelli et al. 1970, Atoji 1962). In the cerium systems, Ce(IV) is present up to 70%, while in the praseodymium case the amount is less and in the lanthanum system the higher oxidation state is absent. This suggests that Ce(IV) and Pr(IV) do assist in preventing the catenation that leads to acetylide ion formation. However, the reviewers suggest that this factor is probably minor while the size factor of the rare earth atom is essential. 

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