The Effect of Composition on the Properties of Semiconducting Transition Metal Nitrides
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1040-Q09-01
The Effect of Composition on the Properties of Semiconducting Transition Metal Nitrides Moreno-Armenta G. Maria, Reyes-Serrato Armando, and Soto H. Gerardo Centro de Ciencias de la Materia Condensada, Universidad Nacional Autonoma de Mexico, Apartado Postal 356, Ensenada, B.C., 22800, Mexico ABSTRACT Using the full potential linearized augmented plane wave (FP-LAPW) method, we investigate the bulk structural and electronic properties in the scandium-, yttrium-, and coppernitrides over a wide range of nitrogen concentrations. The N atom was gradually incorporated into metal matrix with and without metal vacancies. The ground state properties like densities of states (DOS) and formation energies are determined for each calculated alloy. We have found that the semi-conducting state in copper nitride have a tinny compositional margin. Any deviation of the ideal stoichiometry will produce a metallic character. What is more, the stabilities of the conductive phases are very close to the stability of the semi conducting phase, with a little margin favorable to the conducting phases. The calculations of scandium- and yttrium nitrides show, that for very low nitrogen incorporations, the hexagonal and fcc phases may coexist. However, for high nitrogen concentration the cubic phases are favored. For nonstoichiometric nitrogen content, the materials behave as metal, whereas at stoichiometric composition the DOS becomes zero at Fermi level (EF), confirming in this way the semiconductor character of these nitrides. INTRODUCTION Research in transition metal nitrides (TMN’s) has become an important topic over the past years, not merely by its technological applications; it also has a high impact in basic science. The TMN’s can be either metals or semiconductors. However, for some nitrides for example, ScN and Cu3N there has been a long-term debate in the literature, about if they are semiconductors or conductors [1,2]. This combination of properties has attracted a large number of experimental and theoretical investigations. The structures of the metals from group IIIB and their nitrides are fcc, or hcp. The N atoms are located at the interstitial sites of the metal lattice in the octahedral geometry. The NaCl-like structure is associated with the Fm3m spatial group (225), with one sub-lattice in the 4a (0 0 0) and the other one in the 4b (½ ½ ½ ) Wyckoff position. While, Cu3N crystallizes in a cubic anti-ReO3 type structure (space group Pm3m), in which the copper and nitrogen atoms occupy the 3d (½ 0 0) and 1a (0 0 0) Wyckoff position, respectively. This arrangement leaves a significant vacant site in its cube-center sites (1b Wyckoff position), which, can be filled by foreign atoms or by copper atom. In the last case, where Cu occupies the 1b position, the Cu4N compound is formed. The Cu4N looks similar to one ordinary transition metal nitrides with NaCl- like structure (such as ScN, YN) but with a considerable number of vacancies in the Nsites. The ionic character of the N-atoms explains to some extent the preferenc
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