ULTRASONIC VELOCITY STUDIES OF VANADIUM-SESQUIOXIDE
Abstract
The elastic stiffness moduli of pure single crystal V(,2)O(,3) at 296K are determined up to 4 kbar from measurements of the travel times of 30 MHz ultrasonic waves. Linear pressure dependences are found for all modes. Four elastic constants C(,11), C(,12), C(,13), and C(,33) have large positive pressure dependences. Comparison with results for (alpha)-Al(,2)O(,3) indicate that these large dependences are due in part to the highly anisotropic contraction of V(,2)O(,3) under pressure. The softening with pressure of the shear elastic stiffness C(,ST) suggests that a high pressure transition occurs in V(,2)O(,3) between 150 and 250 kbars. Using the values and pressure dependences of C(,11), C(,12), C(,13), and C(,33) we calculate the changes in lattice parameters with pressure up to 140 kbar. Our results are compared with x-ray data of others. The elastic stiffness moduli of V(,2)O(,3) are also determined between 300 and 640K from measurements of the travel times of 30MHz and 150MHz ultrasonic waves. Unusual behavior is found. Elastic constants C(,11), and C(,12), and the bulk modulus each goes through a deep minimum at 540K, in the region of the high temperature electrical transition. Some modes soften drastically between 300K and 540K and then less strongly at higher temperatures. Two shear modes stiffen monotonically with temperature. C(,44) is observed to increase very slightly with temperature near room temperature, go through a maximum, then pass through a minimum near 540K. These results are discussed in the context of the high and low temperature electrical transitions in V(,2)O(,3).
Degree
Ph.D.
Subject Area
Condensation
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