Y. Watanabe
Institute of Materials Research, Tohoku University, Sendai 980, Japan
J. Appl. Cryst. 27, 1040 (1994).
The temperature dependence of the lattice constant for the parent phase in metallic sodium, which has a body-centered cubic (b.c.c.) structure, has been measured by an X-ray single-crystal diffraction method over a range of 20 to 293 K. An abnormal change of the lattice constant at around 40 K is shown, which is attributed to small regions of the low-temperature phase. On the other hand, the value of the full width at half-maximum (FWHM) for the (110)b.c.c. Bragg refrection increased gradually with decreasing temperature and then changed drastically at around 40 K. This results was inconsistent with the neutron diffraction one: the value was constant down to the phase-transition temperature and changed drastically at that temperature. The FWHM for the X-ray experiments is very sensitive to the size of the specimen and sample mount because the external strain originaing from contraction of the sample holder is often introduced into the specimen.
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FIG.1 Normalized lattice constant a(T)/a(300), where a(T) is the lattice constant for the parent phase at temperature T (K). The room-temperature value, a(300), is found to be 4.288(1) [A]. |
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FIG.2 Full width at half-maximum of the (110)b.c.c. Bragg reflection versus temperature T (K). |
References
ABE, H., OHSHIMA, K., SUZUKI, T., HOSHINO, S., & KAKURAI, K., (1994). Phys. Rev. B 49, 3739-3745.
BERLINER, R., FAJEN, O., SMITH, H. G. & HITTERMAN, R. L. (1989). Phys. Rev. B 40, 12086-12097.
KUROIWA, Y., OHSHIMA, K. & WATANABE, Y. (1990). Phys. Rev. B 42, 11591-11597.
WATANABE, Y., TOYOTA, N., INOUE, T., KOMATSU, H., & IWASAKI, H. (1988). Jpn. J. Appl. Phys. 27, 2218-2223.
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