Electric field gradients and impurity distributions in doped noble metals : a systematic study

Abstract

The electric field gradients created at 111Cd nuclei by dilute transition-element impurities in noble metais are studied by the technique of time-differential perturbed angular correlation. The present results supplement previous ones with data for the alloys CuRh, CuPt, AgRh, Aglr, AuRh, AuPd, and AuPt, including temperature and concentration dependence in some typical cases. The results show conclusively that, for most impurities situated to the left of the host noble metais in the Periodic Table, there is a strong attraction between the probe In and the impurity atoms. The binding energy ∆E8 for the probe-impurity system is measured for the Cu R h and Cu Pt alloys. The temperature dependence o f the high-frequency quadrupole interaction vh due to a single-impurity nearest neighbor to the probe is found to obey the usual empiricallaw v( T) = v(O) ( 1-α T3/2 ). The wealth o f experimental data thus made available allows a systematic examination of the results from which the following facts emerge: (i) The observed high frequency v h is related to the nominal valence difference ∆Z between impurity and host and to a parameter ʎ, the difference in the period of impurity and host in the Periodic Table; (ii) a correlation of ∆E8 with both ∆Z and ʎ is apparent; and (iii) an in verse correlation between the a parameter and ∆E8 is apparent.