HIGH PRESSURE POLYMORPHIC TRANSITIONS OF BISMUTH OBSERVED BY THE ULTRASONIC VELOCITY MEASUREMENT

Abstract

Experimental method for determination of the ultrasonic velocity at very high pressure was studied. Single stage piston-cylinder apparatus was used as the high pressure chamber. Maximum pressure of 32 kb was attained easily without any trouble at room temperature. It is expected that this method will be available up to 40 kb combined with temperature of 1000℃. High pressure polymorphism of bismuth which is accompanied with the abrupt change of the elastic wave velocity was examined. Shear wave velocity Vs was decreased extremely at the transition point Bi I-II, and increased again at Bi II-III, though the change of dilatational wave velocity Vp was almost negligible. It was shown that the velocity change of shear wave resembles remarkably with the electric resistance change.