Kj. Range et al., STUDIES ON AB(2)-TYPE INTERMETALLIC COMPOUNDS .5. THE CRYSTAL-STRUCTURE OF MG9SN5, A SUPPOSED HIGH-PRESSURE MODIFICATION OF MG2SN, Journal of alloys and compounds, 244(1-2), 1996, pp. 170-174
Single crystals of Mg9Sn5 have been obtained from the elements by high
-pressure high-temperatures reaction in a modified Belt-type apparatus
(Ta capsule, 50 kbar, 1400-->500 degrees C, and subsequent quenching
to ambient conditions). The compound crystallizes trigonally, space gr
oup R3, with a = 13.222(2), c = 13.150(2) Angstrom, c/a = 0.9946 and Z
= 6. Final residuals after refinement against F-2 were R(1) = 0.0297,
wR(2) = 0.0811 and S = 0.927 for 85 refined parameters and 975 unique
reflections. The crystal investigated showed obverse-reverse twinning
and a pronounced pseudo-symmetry. The crystal structure of Mg9Sn5 com
prises a framework of magnesium atoms with an arrangement similar to t
hat found in Fe2P. The tin atoms are accommodated in tunnels running a
long the c-axis. Mg9Sn5 is at least very similar, perhaps even identic
al, with the ''dense form of Mg2Si'', Mg2Si-II, described by Cannon an
d Conlin (1964) and Dyuzheva et al. (1972, 1995).