Vol. 5, No. 11, Novemher 1966
DEFECTSTRUCTURE AND BONDING OF ZIRCONIUMNITRIDE 2027 CONTRIBUTION No. 8 FROM
THE
GRADUATE CENTERFOR MATERIALS RESEARCH, UNIVERSI.TY 01” MISSOURI, ROLLA,MISSOIJRI
The Defect Structure and Bonding of Zirconium Nitride Containing Excess Nitrogen1 BY M. E. STRAUMANIS, C. A. FAUNCE,
AND
W. J. JAMES
Received April 9,1966 Zirconium nitride, containing 2.0 wt % Hf, is found to have a25 = 4.57560 f 0.00005 A (refraction correction included) and a linear thermal expansion coefficient CY = 5.28 X deg-l (IO-60’). Its composition is (Zr, 2y0 Hf)o.9s10.03K,experi- ~X-ray density of the stoichiometric compound is 7.284 g cm-3). The unit mental density dzp = 6.884j=0.003 g ~ m (the cell contains 3.913 molecules with 3.5% of all sites (8/unit cell) vacant in the cationic and 1.1% in the anionic ( N ) sublattice. The excess of N atoms over the stoichiometric formula is 0.19 atom/unit cell. From purely chemical considerations the bonding appears to be more ionic than metallic and may be described as involving various electronic states of nitrogen (N3-, NO), imposing a high degree of ionic character on the nitride. However, no quantitative value could be assigned to the degree of ionic bonding.
The phase diagram for zirconium and nitrogen was developed by Domagala, et a1.;2a i t showed an a-solid solution and a ZrN homogeneity phase of a range smaller than that for Further investigation by Juza, et. ~ l .revealed , ~ the possibility of an excess nitrogen phase of the composition ZrsNe. The Z N phase may contain defects in the form of vacancies as do TiN and T i 0 . 4 Since ZrN closely resembles TiN, the problems of bonding are similar. Klemm and Schiith,j Philippj6 and Pearson7 have proposed metallic bonding in TiN and ZrN, whereas Baughan8 concluded from the lattice energy that the bonding was ionic. Goward and Hershensong and O’KeefelO pointed out that the experiments of Philipp were inconclusive. Samsonov and Verkhoglijadovall are of the opinion that the bonding is a t least in part ionic. The intention of the present investigation was to study the defects in zirconium nitride (with excess N) by the lattice parameter and density method and to come t o some conclusion concerning the bonding in ZrN on the basis of chemical behavior. Material Zirconium nitride (from the Carborundum Metals Co., Akron, N. Y.) was a dark gray-brown powder with a greenish tint, displaying under the microscope a golden, metallic color. The composition (in %) of the ZrN batch was as follows: metallic impurities (Fe, Al, Cr, Mg, etc.), 0.27; Hf, 2.0; N, 11.6; Zr, 86.13. Inasmuch as the sample was later analyzed, the (1) Presented a t the Seventh General Assembly of the International Union of Crystallography in Moscow, July 18, 1966. (2) (a) R. F. Domagala, D. J. McPherson, and M. Hansen, Tvans. A I M E , 208, 98 (1955); (b) P. Ehrlich, Z . Anovg. Allgem. Chem., 269, l ( 1 9 4 9 ) . (3) R. Juza, A. Rabenau, and I. Nitschke, ibid., 882, 1 (1964). (4) M. E . Straumanis and H. W. Li, ibid., 806, 143 (1960). ( 5 ) W. Klemm and W. Schiith, ibid., 201, 24 (1931). (6) W. Philipp, Acta Met., 10, 583 (1962). (7) W. B. Pearson, ibid., 10, 1123 (1962). (8) E. D. Baughan, Tvans. Favaday Soc., 6 6 , 736, 2025 (1959). (9) G. W. Goward and H. M. Hershenson, Acta Met., 11, 637 (1963). (10) M. OKeefe, ibid., 11, 638 (1963). (11) G. V. $amsonov and T. S. Verkhoglijadova, Dopovidi Akad. Nauk Ukv. R S R , 1, 48 (1962).
knowledge of the Hf content was important. Since ZrN and HfN differ in lattice parameters by only 1.4y0 (4.5756 - 4.5118 = 0.0638 A), they form, according to Duwez and Ode11,12 a continuous series of solid solutions. Therefore the 2% Hf content increased the atomic mass of Zr from 91.22 to 92.12. The influence of other impurities (0.27Y0) was disregarded. Lattice parameter and density determinations were made to detect the defects in the nitride. Lattice Constant and Expansion Coefficient The nitride samples produced sharp X-ray powder lines. However, only chromium Kp radiation (A 2.08059 kx) gave a p331 line suitable (0 83’) to measure precisely the lattice constant (at 10.0, 30.0, 40.0, 50.0, and 60.0’). The 64-mm camera containing the sample was placed into a thermostat for a 40-min exposure by the X-ray beam. As the powder mount was
