S. Tanigawa

Studies of defects at thermal equilibrium and melting in Cu and Ni by positron annihilation

Peak counting rates in the angular correlation were measured as a function of temperature above room temperature in the solid and liquid phases of Cu and in the solid phase of Ni. The peak counting rates in Cu increased about 17% upon melting. Temperature dependence of the peak counting rates in the liquid phase shows a hump at 1150 degrees C. Two possible explanations were proposed for this anomaly. The data in the solid phases were numerically analysed by the trapping model in which it was assumed that only single vacancies and divacancies are effective. The data at lower temperatures, where the effect of divacancies is sufficiently small, were analysed by the conventional trapping model of single vacancies. The results of both analyses are consistent. The characteristic temperature Tc in the trapping model was defined. It was demonstrated that Tc is proportional to E1VF. The experimental values of Tc were plotted against E1VF for various FCC metals and linear relationship between E1VF and Tc was also experimentally found.

Recovery study of copper electron irradiated at 130 K by positron lifetime

Abstract The annealing behavior of election irradiated copper was studied by means of positron lifetime. In Stage III recovery, the long-lived component appeared in the lifetime spectrum. It was attributed to the formation of three-dimensional micro voids. Therefore it is concluded that vacancies are migrating in this temperature range. The lifetime component corresponding to micro voids remains up to a rather high temperature annealing. In addition to micro voids, the existence of other kinds of defects was concluded from the detailed analysis of the lifetime data. The defects formed in Stage III disappeared at high temperature but below the temperature of annealing out of micro voids. These defects were attributed to vacancy loops. Vacancy loops were also formed through the vacancy clustering in Stage III.

Evaluation of the formation entropy of a single vacancy by means of positron annihilation

Abstract Analyzing positron annihilation data it was found that the formation energy of a single vacancy is proportional to the characteristic temperature Tc in f.c.c. metals. Assuming that the equilibrium fractional concentrations of single vacancies at Tc are constant, one finds that the formation entropy of a single vacancy is (1.6 ± 0.1)k for all f.c.c. metals. For zinc and cadmium, the formation entropies are 2.5k and 3.3k respectively.

Positron annihilation study of order-disorder transformation in Cu alloys

Abstract The anomalous change of N 0 ( T ) (the peak counting rates of angular distribution as a function of the temperature of a speciment) due to order-disorder transformation is observed in various Cu-based alloys. The detailed behavior of N 0 ( T ) in AuCu 3 is clearly different from those in CuZn or Cu-Pd alloys, which is attributed to the difference of the order of order-d disorder transformation.

Studies of vacancies and vacancy-impurity pairs in Cu-0.5 at. % Ge by means of positron annihilation

Positron annihilation in Cu-0.5 at. % Ge as a function of measuring temperature has been studied. By the use of the trapping model, the formation energy of a vacancy in copper and the binding energy between a germanium atom and a vacancy have been determined to be 1.28 and 0.27 eV, respectively.

The measurement of the formation energy of a vacancy in Cu by positron annihilation

The temperature dependence of the coincidence counting rates of two annihilation photons was measured for Cu at theta =0. Analysing the results by the trapping model, the formation energy of a vacancy in Cu was determined to be 1.17+or-0.07 eV. This value is in good agreement with that by Simmons and Balluffi (1963).

The Fermi surfaces of CuNi alloys by positron annihilation with crossed-slit geometry

Abstract The Fermi surfaces of Cu and CuNi alloys have been studied by positron annihilation with crossed-slit geometry. The results suggest that the Fermi surface detaches from the Brillouin zone boundaries for 78.7 Cu - 21.3 Ni and 58.1 Cu - 41.9 Ni alloys.

The effect of divacancies on positron annihilation in Cu

The effect of divacancies has been observed on the temperature dependence of gamma - gamma angular correlation of positron annihilation in copper. The peak counting rates of the angular correlation are higher at temperatures near the melting point than those predicted by the trapping model assuming that only single vacancies exist. Numerically analysing the results by the trapping model including divacancies, the formation energy of a single vacancy and the binding energy of a divacancy were estimated to be 1.28+or-0.06 eV and 0.3+or-0.1 eV, respectively.

The effect of lattice vacancies on positron annihilation in copper-nickel single crystals

Abstract A remarkable effect of lattice vacancies on positron annihilation was found in single crystals of Cu-22at.%Ni and Cu-39at.%Ni. This is probably due to the local enhancement of annihilation at the vacancy sites, where the conduction electrons are nearly free.

Positron study of the martensitic transformation in Fe-29.5at.%Ni

Precision measurements of positron lifetime spectra in Fe-29.5at.%Ni alloy specimens were performed to clarify the nature of the martensitic transformation in this alloy. The forward transformation did not introduce any defects which behave as strong trapping sites for positrons. On the other hand, the reverse transformation accompanied the production of defects, to which the positron lifetime is sensitive, maybe dislocations. From the present results, the nature of the transformation was discussed.