Hydrogen diffusion in Fe0.5Ti0.5 -: Quantum isotope effect

A quantum mechanical theory has been used to workout the Quantum Isotope Effect (QIE) on activation energy of the intermetallic compound Fe0.5Ti0.5. The QIE has been calculated with the assumption that the hydrogen isotopes move as ions which diffuse interstitially in the crystal potential computed with the screened Coulomb interaction between proton and host ions. The QIE arises from the quantum mechanical zero point energy associated with the confining potential at the saddle point in the interstitial channel. In Fe0.5Ti0.5 system, the inequality E-a.H > E-a.2H > E-a.3H in activation energy is reversed. QIE values have been calculated for various pressures ranging from normal to 2.5 GPa. A remarkable agreement between theory and experiment is observed. The value of QIE slightly increases with pressure. In this compound, hydrogen prefers the octahedral position and diffuses by O - O jump mechanism.