Inorg. Chem. 2005, 44, 6680−6690 The Indium Subnitrides Ae6In4(InxLiy)N3-z (Ae ) Sr and Ba) Mark S. Bailey, Daniel Y. Shen,† Michael A. McGuire,‡ Daniel C. Fredrickson, Brian H. Toby,§ Francis J. DiSalvo,* Hisanori Yamane,| Shinya Sasaki,⊥ and Masahiko Shimada⊥ Department of Chemistry and Chemical Biology, Cornell UniVersity, Ithaca, New York 14853 Received April 21, 2005 The indium nitrides Sr6In4(In0.32Li0.92)N2.49 and Ba6In4.78N2.72 have been synthesized from an excess of molten sodium. They crystallize in a stuffed variant of the η-carbide structure type in the cubic space group Fd3hm with Z ) 8. The lattice parameters are a ) 14.3752(4) and 15.216(1) Å, with cell volumes 2970.6(2) and 3523.3(6) Å3, respectively. In both compounds there are vacancies on some of the indium and nitrogen sites and, in the case of Sr6In4- (In0.32Li0.92)N2.49, mixed lithium−indium occupancy of one metal site. It is demonstrated that the partial and mixed occupancies act to carefully tune to electron count to almost fulfill the bonding requirements of the stellar quadrangular subnets of both compounds. Four probe resistivity measurements performed upon a pellet of Sr6In4(In0.32Li0.92)N2.49 show it to have a room-temperature resistivity of 6.3 mΩ·cm with a weak temperature dependence. 1 Introduction nitride (InN, Eg ) 0.7 eV ) adopts the same wurtzite structure type as gallium nitride but the standard heat of formation of The binary nitrides of the p-block (M N ) include boron x y indium nitride is -28.6 kJ/mol2, considerably less than that nitride, silicon nitride, and gallium nitride. The M-N bonds of gallium nitride, -156.8 kJ/mol2. This difference in strength within all three compounds are strong and contain a high between the Ga-N and In-N bond results in an interesting degree of covalent character. Furthermore, in bulk form, all schism in the structures and numbers of the alkaline-earth three compounds are relatively inert toward oxide formation (Ae) containing compounds, Ae M N (M ) Ga or In). There when heated in air and are very stable in mildly reducing x y z are almost twice as many reported Ae Ga N 5-13 compounds environments; for example, both hexagonal boron nitride and x y z than Ae In N compounds,13-18 and in the majority of the silicon nitride are commercially useful as crucible materials x y z ternary gallium nitrides, the formal oxidation state of the and diffusion barriers, respectively. The intrinsic materials gallium is either I or III; i.e., it is formally a positive cation. characteristics of GaN are well suited for the high-power semiconductor industry; GaN is a direct, large band gap (3) DiSalvo, F. J.; Clarke, S. J. Curr. Opin. Solid State Mater Sci. 1996, 1 semiconductor (Eg ) 3.4 eV ) with a small unit cell, 1 (2), 241-249. moderately strong gallium-nitrogen bonds, and high carrier (4) Gregory, D. H. Dalton Trans. 1999, 3, 259-270. (5) Yamane, H.; DiSalvo, F. J. Acta Crystallogr. 1996, C52, 760-761. mobility. (6) Cordier, G.; Ho¨hn, P.; Kniep, R.; Rabenau, A. Z. Anorg. Allg. Chem. As the p-block metal, M, becomes heavier, the M-N bond 1990, 591,58-66. 2-4 (7) Park, D. G.; Ga´l, Z. A.; DiSalvo, F. J. Inorg. Chem. 2003, 42 (5), strength decreases considerably; for example, indium 1779-1785. (8) Clarke, S. J.; DiSalvo, F. J. J. Alloys Compd. 1998, 274, 118-121. * To whom correspondence should be addressed. E-mail: fjd3@ (9) Clarke, S. J.; DiSalvo, F. J. Inorg. Chem. 1997, 36, 1143-1148. cornell.edu. (10) Cordier, G. Z. Naturforsch. 1988, 43b, 1253-1255. † Current address: School of Medicine, New York University, New York, (11) Verdier, P.; L’Haridon, P.; Maunaye, M.; Marchand, R. Acta Crys- NY 10016. tallogr. 1974, B30, 226-228. ‡ Department of Physics, Cornell University, Ithaca, NY 14853. (12) Cordier, G.; Ludwig, M.; Stahl, D.; Schmidt, P. C.; Kniep, R. Angew. § NIST Center for Neutron Research, National Institute of Standards and Chem., Int. Ed. Engl. 1995, 34 (16), 1761-1763. Technology, Gaithersburg, MD 20899-8563. (13) Ho¨hn, P.; Ramlau, R.; Rosner, H.; Schnelle, W.; Kniep, R. Z. Anorg. | Institute for Interdisciplinary Research, Tohoku University, 6-3 Aramaki, Allg. Chem. 2004, 630, 1704. Aoba-ku, Sendai 980-8578, Japan. (14) Kirchner, M.; Wagner, F. R.; Schnelle, W.; Niewa, R. Z. Anorg. Allg. ⊥ Institute for Multidisciplinary Research for Advanced Materials, Tohoku Chem. 2004, 630, 1735. University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. (15) Bailey, M. S.; DiSalvo, F. J. J. Alloys Compd. 2003, 353, 146-152. (1) Yu, K. M.; Liliental-Weber, Z.; Walukiewicz, W.; Shan, W.; Ager, J. (16) Cordier, G.; Ro¨nninger, S. Z. Naturforsch. 1987, 42b, 825-827. W., III; Li, S. X.; Jones, R. E.; Haller, E. E.; Lu, H.; Schaff, W. J. (17) Yamane, H.; Sasaki, S.; Kajiwara, T.; Yamada, T.; Shimada, M. Acta Appl. Phys. Lett. 2005, 86, 071910-1-071910-3. Crystallogr. 2004, E60, i120-i123. (2) Ranade, M. R.; Tessier, F.; Navrotsky, A.; Marchand, R. J. Mater. (18) Schlechte, A.; Prots, Yu.; Niewa, R. Z. Kristallogr.sNew Cryst. Struct. Res. 2001, 16 (10), 2824-2831. 2004, 219, 349-350. 6680 Inorganic Chemistry, Vol. 44, No. 19, 2005 10.1021/ic050613i CCC: $30.25 © 2005 American Chemical Society Published on Web 08/25/2005 Indium Subnitrides Ae6In4(InxLiy)N3-z In all the reported AexInyNz compounds, such as Ca19- 14 15 17 In8N7, Ca2InN, and Ba19In9N9, there is insufficient nitrogen to fully oxidize the metals; indeed, the formal oxidation state of the indium is negative and indium-indium bonding is apparent. Gallium-gallium bonding occurs only 10 11 in Ca5Ga2N4 and CaGaN, the two AexGayNz compounds that contain Ga(I), and in the few compounds that contain 12 anionic gallium, (Ae6N)Ga5 (Ae ) Sr, Ba) and Ca7- 13 Ga1+δN4. However, the most significant difference between the ternary indium and gallium nitrides is that none of the Ae In N compounds exhibit direct indium-nitrogen bonds. Figure 1. Stella quadrangula formed from capping every tetrahedral face x y z of an inner tetrahedron. 13 13 In only Ca7Ga1+δN4, which is isotypic to Ca7In1+δN4, and 12 (Ae6N)Ga5 (Ae ) Sr, Ba) are there no gallium-nitrogen 27 28 bonds. Direct indium-nitrogen bonding is also absent in all transition-metal nitrides such as Co3Mo3N and Fe4W2N, of the known multinary indium nitrides such as Sr8Cu3In4- in which the nitrogen atoms occupy the octahedral 16c sites. 19 20 ) 21 - - 29 N5 and R3InN (R Ti, Sc, La Nd, Sm, Gd Tm, Lu). The crystal orbital overlap population (COOP) and the In fact, the only known nitrides to contain a direct indium- very closely related crystal orbital Hamilton population nitrogen bond are InN and its solid solutions with gallium (COHP) analyses30 are very useful electronic structure tools. 22 - nitride, In1-xGaxN; however, indium nitrogen bonds are Both analyses yield information about the bonding or 23 apparent in the cyanamides In2.24(NCN)3 and NaIn(NCN)2. antibonding nature of pairwise interactions in solids. They 24 25 The NaBa and Ti2Ni structures are closely related. Both thus allow the local bonding interactions of an extended solid h are cubic, space group Fd3m, and contain 96 atoms in the to be isolated and analyzed. Just as in molecules, these unit cell. The atoms occupy the same three Wyckoff interactions can be bonding or antibonding and, as noted by positions, namely the 48f, the 32e, and the 16d sites (using Dronskowski,31 nature always attempts to maximize the h assignments with the origin at 3m, origin setting 2). In both filling of bonding states and to minimize the filling of compounds, the 48f and the 32e sites are occupied by antibonding states. This can be achieved in various ways, different elements and it is the nature of the atom that and it often leads to unusual structural features or physical occupies the 16d site that determines the different atomic properties. For example, the ferromagnetism of itinerant ratios of NaBa and Ti2Ni. In the NaBa structure, the sodium electrons in iron, cobalt, and nickel can be explained via atoms occupy the 32e and 16d sites and the barium atoms spin-polarized COHP analysis.31 In another study, COOP the 48f sites. In Ti Ni the nickel atoms occupy only the 32e 2 analysis makes apparent the source of the decreasing lattice sites and the titanium atoms occupy both the 48f and 16d parameter in the series of compounds Ti TBi (T ) Cr, Mn, sites. 4 2 Fe, Co, and Ni), a decrease larger than that expected from The distribution of the 16d, 32e, and 48f sites in the NaBa the change of size of the T atom. The COOP analysis and Ti Ni structures can be visualized in terms of two distinct 2 revealed that although the Ti-Bi interactions remain strong subnets. The 32e and 16d sites generate a framework of throughout the series, the T-T bonding increases as the extra corner-sharing stellae quadrangulae or tetracapped tetrahedra, electrons funnel into the d-d bonding of these elements.32 an example of which is shown in Figure 1. The 48f sites Hence the contraction of the lattice parameter has a physical create a three-dimensional network of face-sharing octahedra that define two distinct vacancies at their centers, at the 16c and an electronic root. and 8a positions. Occupation of the 16c site within the In this paper we introduce the isostructural compounds octahedral network leads to the η-carbide (W3Fe3C) structure Sr6In4(In0.32Li0.92)N2.49 and Ba6In4.78N2.72.