Springer Online Journal Archives 1860-2000
Abstract Perturbed angular correlation of gamma rays (PAC) was applied to measure concentrations of point defects in quenched and milled intermetallic compounds. Two systems with high ordering energies were studied, PdIn and NiAl, with principal results obtained for PdIn. The defects, lattice vacancies and antisite atoms, were detected by quadrupole interactions induced at nuclei of nearby In/Cd probe atoms. Measurements on annealed, quenched and milled samples are compared to identify quadrupole interaction signals with specific configurations of defects near probe atoms. Müller and Hahn had previously identified signals with a Pd-vacancy in the first near-neighbor shell of the In probe and a Pd-antisite atom in the second shell. Six additional signals are identified in this work, including two distinct configurations of two Pd-vacancies in the first shell, a Pd-vacancy in the fourth shell, an In-vacancy in the second or third shell, and an In-antisite atom in the first shell. After quenching, observation of both Pd and In-vacancies after quenching from 1100-1500 K demonstrates that the high temperature equilibrium defect is the Schottky vacancy pair. An activation energy of 0.91(18) eV was determined for formation of a Schottky pair. After milling, the site fraction of probes having one Pd-vacancy in the first shell increased rapidly and saturated at a value of about 20%. This implies a Pd-vacancy concentration of about 3.3 at.%, with a corresponding enthalpy of the order of 3 kJ mol−1, making a significant fraction of the excess enthalpy in the milled intermetallic. After milling NiAl, a Ni-vacancy concentration of order 1–10 at.% was observed. A comparison is made of defect combinations observed after mechanical milling of PdIn and NiAl by PAC and of other intermetallics by Mössbauer spectroscopy. Dominant defects produced by milling are the Schottky pair for PdIn, triple defect for NiAl and FeRh and antisite atom pair for FeAl.
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