T. E. Antonova

On the isomorphous phase transformation in the solid f.c.c. solutions CoH at high pressures

Abstract Samples of Co containing 0.2 at.% Fe and consisting of a mixture of approximately equal amounts of the h.c.p. (stable) and f.c.c. (metastable) phases were loaded with hydrogen by a 24 h exposure to a hydrogen atmosphere at 325°C and pressures up to 9 GPa. X-ray diffraction at ambient pressure and 100 K has revealed a steep increase in the lattice parameter of the f.c.c. phase in the samples hydrogenated at 4–6 GPa, corresponding to an increase in the hydrogen content from few atomic per cent to an H/Co atomic ratio of approximately 0.95. This behaviour is interpreted as a supercritical anomaly of an isomorphous phase transformation in the f.c.c. solid solutions. The topology of the T-P phase diagram of the CoH system is discussed in view of these observations.

Atomic ordering in the hcp cobalt hydrides and deuterides

Abstract Cobalt hydrides and deuterides with the hcp metal lattice and H(D)-to-metal atomic ratios 0.18≤ x ≤0.5 were prepared under high pressures of hydrogen or deuterium, respectively, and studied by neutron diffraction in a metastable state at 120 K and ambient pressure. A profile analysis of the spectra showed that in all samples the hydrogen and deuterium atoms occupy octahedral interstitial sites. In the samples with x ≤0.26, the hydrogen and deuterium atoms are randomly distributed over these sites. In the samples with x ≥0.34, they form layered superstructures, occupying every third octahedral base layer at x =0.34 and every second layer at x =0.38 and 0.5.

Mössbauer study of the hydrides of Nb3Me with A15 structure

Abstract Hydrides of intermetallic Nb3Me (Me ≡ Au, Ir, Sn) with A15 structure were prepared at hydrogen pressures up to 7 GPa and studied by Mossbauer spectroscopy with the resonances on 197Au (77.3 keV), 193Ir (73.0 keV) and 119Sn (23.9 keV). In all these systems, hydrogenation was found to lead to a reduction in the electron density at the Mossbauer nuclei, but the decrease for 119Sn was much smaller than for 197Au and 193Ir. This difference suggests that in Nb3Au and Nb3Ir the hydrogen occupies interstitial sites which are closer to the metal atoms than those occupied in Nb3Sn.

119Sn Mössbauer study of Mn3SnHx

Abstract Hydrides of the intermetallic compound Mn 3 Sn have been prepared at 350°C and pressures of molecular hydrogen between 2.8 and 4.0 GPa. The hydrides with an approximate composition Mn 3 SnH were found to have a cubic perovskite structure. A 119 Sn Mossbauer study revealed that they are magnetically ordered between 4.2 and 300 K and undergo a magnetic transition at T M ≲200 K.

Site distribution and hyperfine parameters of tin impurities in α manganese

Abstract Dilute alloys of 0.1–0.5 at.% of enriched 119 Sn in α manganese were transformed to hydrides with hcp, fcc and β-Mn structures by exposure to pressures of molecular hydrogen up to 3 GPa at elevated temperatures and subsequent quenching to room temperature. The samples were then transformed back to α-Mn(Sn) by hot extraction of the hydrogen at temperatures up to 400°C. 119 Sn Mossbauer spectra taken after hydrogen extraction differed considerably from those taken before the hydrogen treatment. This observation is interpreted by a strongly different distribution of Sn atoms over the four crystallographically inequivalent sites in the α-Mn structure before and after the treatment. A quantitative evaluation of the Mossbauer spectra yields the hyperfine parameters of 119 Sn on all Mn sites and shows that the preferred tin site is the Mn-I position in the α-Mn structure.