Speaker
Description
In this work, we report on the hyperfine parameters of the implanted 181-Ta probe in the rutile structure of the single crystal TiO2 using the e – γ time differential perturbed angular correlation (e – γ TDPAC) technique. The outcome was compared with γ – γ TDPAC results. The experiments were performed under vacuum within the temperature range of 50 K - 427 K. It is found that after annealing at 873 K, the 181-Ta probe substitutes the Ti lattice site with a unique nuclear quadrupole interaction. This allowed for the precise measurement of the largest electric field gradient (Vzz) and asymmetry parameter (η). The hyperfine parameters that are obtained from the e – γ TDPAC spectroscopy agrees with that of the γ – γ TDPAC spectroscopy at room temperature, apart from a calibration factor, both from our experiments and literature [1][2]. Surprisingly, we have detected a parabolic increase of Vzz with a concave curvature at the low temperature regime (50 K - 427 K), as opposed to the linear increase at the high temperature regime (600 K - 1200 K) as found in the literature [1][2]. We hypothesize that there exist a Vzz maxima at a unique temperature of around 500 K. Although there are precise ab-initio methods that modelled the linear increase at the high temperature regime, there is a lack of such insight for the parabolic increase at the low-temperature regime. Hence, we are performing Density Functional Theory (DFT) calculations on Ta-doped TiO2 considering lattice parameters over a broad temperature range of 0 K – 1200 K to obtain deeper insights into this particular temperature dependence of our experimentally measured Vzz.
References:
1) J. M. Adams and G. L. Catchen, Phys. Rev. B 50, 1264 (1994).
2) G. N. Darriba, L. A. Errico, P. D. Eversheim, G. Fabricius, and M. Rentería, Phys. Rev. B 79, 115213 (2009). Erratum Phys. Rev. B 84, 239903 (2011).
