A Search for Thermal Vacancies Forming Close Frenkel Pairs in Fe-Cr Alloys

The room temperature Mössbauer spectra of $\text{}^{57}$Fe were measured for the bcc Fe$\text{}_{0.948}$Cr$\text{}_{0.052}$ solid solution quenched into water being at about 295 K from different temperatures not exceeding 1000 K, i.e. from the temperatures for which probabilities of formation of "clear" (Schottky) vacancies as well as vacancies forming the separate interstitial-vacancy (Frenkel) pairs are negligibly low. The obtained data were analysed in terms of concentration of unoccupied places in the 14-site surroundings of an $\text{}^{57}$Fe Mössbauer probe in the sample. It turned out that the concentration of vacancies detected by the probe increases with temperature very rapidly - at the rate of about 10$\text{}^{-4}$ K$\text{}^{-1}$. The result may suggest that the Mössbauer probe is sensitive to a possible thermal distortion of the lattice or creation of very close Frenkel pairs (the interstitial is the nearest neighbour of the vacant lattice site)

Positron Annihilation in Obsidians

Positron lifetime spectra as well as one-dimensional angular correlations of positron annihilation radiation were measured at room temperature for samples of rhyolitic obsidian coming from Iceland, Italy and Armenia. The samples were of different age. One specimen (originating from Iceland) was relatively young, formed in 1980. The others were much older, collected during the 19th century. It was found that the linear dimensions of pores trapping the positronium atoms before their decay as well as the pore concentration in all old obsidians are almost the same independently of the place of their formation. Simultaneously the concentration of the pores in the young sample is about five times lower than in the old specimens. Basing on the result it is suggested to extend the study in order to find out if positron annihilation can be used for the investigation of the age of the volcanic accumulations containing obsidian

Thermal defects in iron-based Fe-V solid solutions

Room temperature 57Fe Mössbauer spectra, positron annihilation lifetime data, X-ray diffraction patterns, and energy distributions of X-rays induced by an electron beam were measured for samples of the Fe0.947V0.053 solid solution quenched from different temperatures not exceeding 1250 K, into water being at about 295 K. The data were analysed in terms of concentration of unoccupied sites in the 14-site neighbourhood of the 57Fe Mössbauer probe in the specimens. It was found that the vacancy formation enthalpy amounts to 0.8 š 0.2 eV in the materials studied

A Dilute-Limit Heat οf Solution of Aluminium in Iron Studied with 57Fe\text{}^{57}Fe Mössbauer Spectroscopy

The room temperature $\text{}^{57}Fe$ Mössbauer spectra for binary iron-based solid solutions $Fe_{1-x}Al_x$, with x in the range 0.03 ≤ x ≤ 0.05, were analysed in terms of binding energy $E_b$ between two Al atoms in the Fe-Al system. The extrapolated values of $E_b$ for x= 0 were used for computation of the dilute-limit heat of solution of aluminium in iron. The results were compared with that resulting from the Miedema's model of alloys as well as those derived from the heat of formation of the system, obtained with both calorimetric measurements and theoretical calculations. The comparison shows that our Mössbauer spectroscopy findings are in good agreement with all the other results mentioned above

Positron Annihilation in Tektite and Hyalite

Positron lifetime spectra as well as one-dimensional angular distributions of photons coming from the two-photon annihilation of an electron-positron pair were measured at room temperature for samples of natural tektite and hyalite. The data were used for estimation of positronium characteristics in the specimens. The characteristics were analysed in terms of parameters of pores trapping the positronium atoms before their decay. In the analysis two models of the traps were taken into account, i.e. the square potential wells of spherical symmetry with barriers of finite and infinite heights. It was found that the linear dimensions of the pores resulting from these two-trap models are almost the same and they are of the order of 1 nm

A Dilute-Limit Heat οf Solution of Aluminium in Iron Studied with 57

The room temperature $\text{}^{57}Fe$ Mössbauer spectra for binary iron-based solid solutions $Fe_{1-x}Al_x$, with x in the range 0.03 ≤ x ≤ 0.05, were analysed in terms of binding energy $E_b$ between two Al atoms in the Fe-Al system. The extrapolated values of $E_b$ for x= 0 were used for computation of the dilute-limit heat of solution of aluminium in iron. The results were compared with that resulting from the Miedema's model of alloys as well as those derived from the heat of formation of the system, obtained with both calorimetric measurements and theoretical calculations. The comparison shows that our Mössbauer spectroscopy findings are in good agreement with all the other results mentioned above