Effect of hydrogen on the temperature dependence of the elastic constants of vanadium single crystals

The changes in the absolute values of the elastic constants C', C/sub L/ and C44 by the ultrasonic technique over the temperature range 144--320 K with varying amounts of hydrogen in Vanadium up to 1.5 at.% have been determined. In the α phase, the changes in the absolute values of C' and C/sub L/ were found to be linear with negative slopes of 2.0% and 0.5%/at.% H, respectively. The changes in C44 in the α phase varied between 0 and 0.5 or 0.9% H. The bulk modulus and Voight-Reuss average Young's modulus in that phase were found to decrease 0.70% and 0.65%/at.% H, respectively. The elastic constants in the temperature range of the α phase exhibited no change in their temperature dependences by the addition of hydrogen. The present results are compared to the results of other published investigations. The anharmonic effects are discussed in the light of the volume expansion due to H in V upon the elastic constants, the possible electronic effect by suggesting the addition of H to V is analogously similar electronically to adding Cr to V and finally the Snoek relaxation effect. It is concluded that the Snoek relaxation best describes the ΔC' effect observed when hydrogen is present in the α phase. This effect yields an asymmetric distortion energy parameter [3(A-B)/(A+2B)] of the order of 0.47