Electrical resistivities and specific heats were measured in alloys which contained 30, 38, 43 or 48at%Al and had D03 (Fe3Al) or B2 (FeAl) structures. A knife-edge method was used at 25C, and a pulse-heating method at 25 to 1100C. The resistivity values were identical for step-cooled (over several days) and quenched (from 1000C) samples; except for a slight increase for the 48at%Al alloy when cooled at 1.5C/s, or quenched. This was suggested to be due to the high thermal vacancy concentrations in this alloy. Within the D03 structural composition range, the resistivity at 25C increased with Al content; due to the filling of holes in the narrow d-band by electrons from Al atoms. However, in the B2-structure range, the resistivity decreased with Al content; due to a lesser scattering of electrons caused by decreasing Fe-Fe nearest-neighbor clusters. The resistivity and specific heat were measured simultaneously by using pulse-heating calorimetry. The resistivity versus temperature behavior of these alloys up to 1100C was found to resemble the resistivity saturation phenomenon which was observed for disordered metal alloys. This suggested that the antisite defect affected the resistivity more than did vacancies. An interesting feature of the resistivity versus temperature curves was a decrease, in the thermal coefficient of resistance, with decreasing Al content; becoming negative at 30at%Al. The specific heats of all of the alloys exhibited a marked (25%) increase at high temperatures; presumably due to defect formation. The temperature at which the deviation occurred was heating-rate dependent. The specific heat versus temperature data were used to determine the energy of formation of the defects, which varied linearly from about 130J/mol at 30at%Al to 95J/mol at 48at%Al. By assuming triple defect formation, the vacancy concentration was determined and was found to be in excellent agreement with published values.

The Formation of Defects in Fe-Al Alloys Electrical Resistivity and Specific Heat Measurements. M.Kass, C.R.Brooks, D.Falcon, D.Basak: Intermetallics, 2002, 10[10], 951-66