Electronic structure of the sigma-phase in paramagnetic Fe-V alloys. Experimental and theoretical study

The electronic structure of $\sigma$-phase Fe$_{100-x}$V$_x$ compounds with 33.3 $\le x \le 60.0$ was calculated from the charge self-consistent Korringa-Kohn-Rostoker method. For the first time, charge densities $\rho_A(0)$ and electric field gradients were determined at Fe nuclei, that occupy five nonequivalent lattice sites. The highest $\rho_A(0)$ values were found on sites A and D, and the lowest one on site B, the difference ranging between 0.162 and 0.174 $\it s$-like electrons per Fe atom for $x = 33.3$ and $x = 60$, respectively. The calculated quantities combined with experimentally determined site occupancies were successfully applied to analyze $^{57}$Fe M\"ossbauer spectra recorded on a series of 8 samples in a paramagnetic state.Comment: 4 pages, 4 figures, 15 reference

Debye temperature of disordered bcc-Fe-Cr alloys

Debye temperature, TD, of Fe100-xCrx disordered alloys with 0<x<99.9 was determined from the temperature dependence of the centre shift of 57Fe Mossbauer spectra recorded in the temperature range of 80-300K. Its compositional dependence shows an interesting non-monotonous behaviour. For 0<x<~45 as well as for ~75<x<~95 the Debye temperature is enhanced relative to its value of a metallic iron, and at x=~3 there is a local maximum having a relative height of ~12% compared to a pure iron. For ~45~95 the Debye temperature is smaller than the one for the metallic iron, with a local minimum at x=~55 at which the relative decrease of TD amounts to ~12%. The first maximum coincides quite well with that found for the spin-waves stiffness coefficient, D0, while the pretty steep decrease observed for x>~95 which is indicative of a decoupling of the probe Fe atoms from the underlying chromium matrix is likely related to the spin-density waves which constitute the magnetic structure of chromium in that interval of composition. The harmonic force constant calculated from the Debye temperature of the least Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of a pure chromium.Comment: 15 pages, 7 figures, 26 reference

Short-Range Order in Fe-Rich Fe-Cr Alloys as Revealed by M\"ossbauer Spectroscopy

Distribution of Cr atoms in Fe_{100-x}Cr_x alloys with x \le 25 within the first two coordination shells, 1NN-2NN, around probe 57Fe atoms was studied by means of the M\"ossbauer Spectroscopy. Clear evidence was found that the distribution is characteristic of a given atomic configuration. Only the configurations with Cr atoms situated in 2NN exhibit a quiasi-random distribution, while those with Cr atoms present in 1NN shell and those with Cr atoms in both shells is evidently not random showing clastering or anticlastering features. These findings are novel and much more complete than the up-to-date knowledge according to which there is an inversion of the short-range order parameter at x = 11. The inversion in the present study was found only for the configuration with one Cr atom in 1NN. On average, Cr atoms are distributed almost randomly within the 1NN-2NN volume for x \eq ~10, and do cluster for larger x.Comment: 4 pages and 4 figure