ULTRASONIC ATTENUATION IN SODIUM AT LOW TEMPERATURES.
CALIFORNIA UNIV LOS ANGELES DEPT OF PHYSICS
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The ultrasonic attenuation in a wire sample of sodium was measured by pulse-echo and resonant techniques over a temperature range of 2 -77K at frequencies of 200-300 kc in order to investigate the effects of the martensitic transformation and the electron-lattice interaction. The onset of the transformation into the h.c.p. structure was indicated by an increase in the attenuation which then decreased as absolute zero was approached. The attenuation displayed a large temperature hysteresis, reverting irreversibly into the high temperature phase, b.c.c. at about 52K. Qualitative agreement with theory was found for the electron-lattice interaction. A metastable state of sodium was formed during extrusion of the sodium wire at liquid nitrogen temperatures which consisted of body-centered cubic and hexagonal close-packed structures as evidenced by ultrasonic velocity, specific heat and x-ray diffraction experiments. The reversion temperature for the metastable state was about 116K at which point it reverted into the b.c.c. structure usually seen at this temperature. Author
- Solid State Physics