THE ZIRCONIUM-TIN SYSTEM, WITH PARTICULAR ATTENTION TO THE ZR5SN3-ZR5SN4 REGION AND ZR4SN

The stoichiometric phases Zr5Sn3 and Zr5Sn4 (both P63/mcm, a = 8.4560 (7), c = 5.779 (1) Å and a = 8.7656 (7), c = 5.937 (1) Å, respectively) are obtained in high yield from powder sintering reactions of Zr and ZrSn2 at 1000 °C. Arc-melted samples over the same composition range give generally complex and diffuse Guinier powder patterns, indicative of continuous distributions of compositions between the maximum melting ~Zr5Sn33 (Zr5Sn3″) and either Zr5Sn3 or ~Zr5Sn4. The arc-melted samples do not improve significantly on annealing at 1000–1100 °C, although the line phases are recovered if the samples are first ground and pelleted. We propose a phase diagram for this region in which the limiting phase fields Zr5Sn3 and Zr5Sn4 merge at high temperature and exhibit a common melting maximum. The overall behavior doubtlessly derives from the close structural relationship between Zr5Sn3 and Zr5Sn4, the latter (Ti5Ga4 type) being an interstitial tin derivative of the former (Mn5Si3 type). The structure of a single crystal that grew from arc-melted Zr5Sn3 was shown to have the intermediate composition Zr5Sn3.18, consistent with the proposed relationships and structures (a = 8.5036 (9), c = 5.820 (1) Å, R/Rw = 1.7/2.0%). The zirconium-richest compound in this system is a line phase with a composition between Zr4 0Sn and Zr4.1Sn. The compound shows weak superstructure reflections that require a doubled cell (a = 11.252 (1) Å) and a more complex structure than the assigned A15 type. Zr4Sn slowly decomposes to α-Zr(Sn) and Zr5Sn3 at 820 °C. © 1990, American Chemical Society. All rights reserved.