A New Conducting Ternary Nitride: NaxTa3N5(0 [less-than or equal to] x [less-than or equal to] 1.4)

Topotactic insertion of sodium into the channel structure of Ta3N5has been accomplished by the reaction between Na and Ta3N5at temperatures between 450 and 600°C in sealed Ni tubes. The limiting stoichiometry of NaxTa3N5obtained isx approximately equals 1.4. The structure of Na1.0Ta3N5has been refined using Rietveld full-profile refinement of X-ray powder diffraction data using the Ta3N5structure as the starting model. The space group remainsCmcm(No. 63) with parametersa=3.995(1),b=10.197(2), andc=10.331(2) A. The Na atoms are shown to occupy 7-coordinate sites in the holes present in the Ta3N5framework. The weak temperature dependence of the magnetic susceptibility between 100 and 320 K of Na1.0Ta3N5and its small value (χmol(300 K)=6.5×10-4emu mol-1) suggest that the compound is a metallic conductor. This is supported by the moderate conduction of an unsintered pellet of Na1.0Ta3N5powder. We also report the identification of the poorly crystalline disordered rock salt phase Na2Ta3N5(a=4.47(4) A) which is obtained when the reaction temperature is between 600 and 800°C and a partly characterized hexagonal phase that results from nitrogen loss, Na1-xTa3+xN4(x approximately equals 0), which forms at temperatures above 800°C. The latter compound crystallizes inP63/mcm(No. 193) witha=5.1784(1) andc=10.3650(3) A and is analogous to previously reported Li and Mg compounds. © 1997 Academic Press.