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The equilibrium phase diagram and crystal structures of the intermediate phases of the Ba-Cd binary system
Journal of the Less-Common Metals, 41 (1975) 193 - 194 @ Elsevier Sequoia S. A., Lausanne - Printed in the Netherlands
193
Letter to the Editor
The equilibrium phase diagram and crystal structures of the intermediate phases of the Ba-Cd binary system
In a Short Communication (J. Less-Common Metals, 39 (1975) 181) R. T. Dirstine has reported on the barium-cadmium phase diagram. It should be noted however, that this system, together with that of calcium-cadmium, has previously been the subject of a study published by Bruzzone (Guzz. Chim. Ital., 102 (1972) 234) and that the work described by Dirstine confirms, but does not add to, the work already published. The phase diagram given by Bruzzone is reproduced in Fig. 1, for comparison.
Cd
10
20
30 ATOMIC
40
50 PERCENT
80
70
80
BARIUM
Fig. 1. Equilibrium phase diagram of the Ba-Cd system. (G. Bruzzone: Gazz. Chim. Ital., 102 (1972) 234.)
Moreover, in contrast to the work described by D&tine, it should be noted: (1) that the uncertainty (dashed lines) indicated on his phase diagram between 65 and 85 at.% Ba is not supported, since the investigation of the crystal structures of the intermediate phases, carried out in the previous work, has demonstrated the existence of the Ba&d compound; this phase crystalhzes with tetragonal symmetry (preliminary cell dimensions, a = 4.2, c = 15.2 A) and is isomorphous with BaaHg. (2) The existence and crystal structure of BaCdz have also been reported (Bruzzone: Rend. Act. Naz. Lincei, 48 (2) (1970) 235).
194
(3) The actual composition of the phase indicated by Dirstine as BaCds agrees more closely with the previous formula BaCd, . 5. The crystal structure of this phase has been studied by M. L. Fornasini and G. Bruzzone (Acta Cry&, B30 (2) (1974) 317). The compound, the composition of which corresponds exactly to BaCdde4s, has a hexagonal sub-cell, space group Pb/mm, with a = 10.740(3), c = 10.200(3) 8, dabs = 7.35 g/cm3. The true unit cell appears to be hexagonal, with double these a and c axes. A reasonable solution for the sub-cell was obtained by the symbolic addition method, using photographic data. The sub-cell contains 7 barium atoms and 31 cadmium atoms, with one set of cadmium positions only partially occupied.
G. BRUZZONE Institute of Physical Chemistry, (Received
January 14, 1975)
University of Genoa, Genoa
(Italy)
193
Letter to the Editor
The equilibrium phase diagram and crystal structures of the intermediate phases of the Ba-Cd binary system
In a Short Communication (J. Less-Common Metals, 39 (1975) 181) R. T. Dirstine has reported on the barium-cadmium phase diagram. It should be noted however, that this system, together with that of calcium-cadmium, has previously been the subject of a study published by Bruzzone (Guzz. Chim. Ital., 102 (1972) 234) and that the work described by Dirstine confirms, but does not add to, the work already published. The phase diagram given by Bruzzone is reproduced in Fig. 1, for comparison.
Cd
10
20
30 ATOMIC
40
50 PERCENT
80
70
80
BARIUM
Fig. 1. Equilibrium phase diagram of the Ba-Cd system. (G. Bruzzone: Gazz. Chim. Ital., 102 (1972) 234.)
Moreover, in contrast to the work described by D&tine, it should be noted: (1) that the uncertainty (dashed lines) indicated on his phase diagram between 65 and 85 at.% Ba is not supported, since the investigation of the crystal structures of the intermediate phases, carried out in the previous work, has demonstrated the existence of the Ba&d compound; this phase crystalhzes with tetragonal symmetry (preliminary cell dimensions, a = 4.2, c = 15.2 A) and is isomorphous with BaaHg. (2) The existence and crystal structure of BaCdz have also been reported (Bruzzone: Rend. Act. Naz. Lincei, 48 (2) (1970) 235).
194
(3) The actual composition of the phase indicated by Dirstine as BaCds agrees more closely with the previous formula BaCd, . 5. The crystal structure of this phase has been studied by M. L. Fornasini and G. Bruzzone (Acta Cry&, B30 (2) (1974) 317). The compound, the composition of which corresponds exactly to BaCdde4s, has a hexagonal sub-cell, space group Pb/mm, with a = 10.740(3), c = 10.200(3) 8, dabs = 7.35 g/cm3. The true unit cell appears to be hexagonal, with double these a and c axes. A reasonable solution for the sub-cell was obtained by the symbolic addition method, using photographic data. The sub-cell contains 7 barium atoms and 31 cadmium atoms, with one set of cadmium positions only partially occupied.
G. BRUZZONE Institute of Physical Chemistry, (Received
January 14, 1975)
University of Genoa, Genoa
(Italy)