Dynamics of an Indium Impurity in the Relaxed Divacancy in Iridium

Abstract

Perturbed y-y angular correlation experiments reveal an unexpected dynamical behavior of U1 ln atoms in a trivacancy complex in iridium. The measured quadrupole interaction is static at 12 K but becomes strongly time dependent around 100 K resulting in a typical damping of the interaction pattern. At 293 K again a static interaction of different magnitude is observed. This behavior can be described by a jump motion of the indium atom between a stable position in the center of the (111) three-vacancy triangle at low temperatures and the surrounding vacant sites at high temperatures.PACS numbers: 61.70. Yq, 66.30.Jt, Since the first applications of nuclear methods to the study of defects in metals, the dynamic behavior of defect-probe-atom complexes has been a main point of interest. The reason is that it is directly related to the mechanism of the elementary diffusion jump in the various host matrices. And in contrast to the classical diffusion studies employing tracer atoms, whose macroscopic distribution is determined, e.g., through sectioning techniques, the nuclear methods are able to give direct information about the movement of the probe atom on a microscopic scale and thus improve our understanding of the diffusion process.Generally, the nuclear methods exploit the hyperfine interaction between the nuclear moments of a probe nucleus and the electromagnetic fields generated by a defect in the vicinity of the probe. In the case of a trapped defect, this causes a static hyperfine interaction, which gives information about the nature of the defect and the geometrical configuration of the probe-defect complex. Distortions of the complex during the time of observation lead to time-dependent hyperfine interactions which can be directly related to the dynamical behavior of the probe atom or its surrounding. In recent review, Petry and Vogl x discuss the application and specific advantages of the various nuclear methods for diffusion studies.The y-y perturbed-angular-correlation (PAC) technique has been particularly successful in the investigation of vacancies in metals. 2~4 It observes the perturbation of the directional correlation of two y rays emitted consecutively in the decay of an unstable parent nucleus. The hyperfine interaction between the quadrupole moment of the nuclear state intermediate to the y-y cascade and electric-field gradients caused by disturbances of the cubic charge symmetry surrounding the probe atom causes a characteristic perturbation pattern. It can be described by a perturbation function of the form "max GnU) = X S2n(T])cOs[c n (7])vnt] .Here VQ ^eQV zz lh is the quadrupole interaction (QI) frequency with Q the quadrupole moment of the inter-mediate nuclear state and V zz the largest component of the electric-field-gradient (EFG) tensor. 5 rj^iVxx -V yy )/V zz varies between 0 and 1 and describes the asymmetry of the EFG. The Fourier coefficients sm and the frequency factors c n are well known functions of r\. 5 rt max is determined by the spins and multipolarities of the levels and tran...

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Electric field gradient study on pure and Cd-doped In(111) surfaces: Correlation between experiments at the atomic scale and first-principles calculations

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