Elastic and structural instability of cubic Sn3N4 and C3N4 under pressure

We use in-situ high pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride Sn3N4 under pressure up to about 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3N4 at a higher pressure of 88 GPa compared to earlier predictions of 40 GPa. Our comparative analysis of cubic nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while it is structurally unstable and should not exist at ambient conditions.Comment: 5 pages, 4 figure

Identification of Retained Austenite in 9Cr-1.4W-0.06Ta-0.12C Reduced Activation Ferritic Martensitic Steel

Reduced activation ferritic martensitic (RAFM) 9Cr steels, which are candidate materials for the test blanket module (TBM) of nuclear fusion reactors, are considered to be air hardenable. However, alloy composition and the processing conditions play a significant role during the transformation of austenite to martensite/ferrite on cooling. The presence of retained austenite is known to influence the mechanical properties of the steel. Identifying very low amounts of retained austenite is very challenging though conventional microscopy. This paper aims at identifying a low amount of retained austenite in normalized 9Cr-1.4W-0.06Ta-0.12C RAFM steel using synchrotron X-ray diffraction and Mossbauer spectroscopy and confirmed by advanced automated crystal orientation mapping in transmission electron microscopy. Homogeneity of austenite has been understood to influence the microstructure of the normalized steel, which is discussed in detail

High pressure x-ray diffraction and extended x-ray absorption fine structure studies on ternary alloy Zn1−xBexSe

International audienceThe ternary semiconductor alloy Zn1−xBexSe has been studied under high pressure by x-ray diffraction and extended x-ray absorption fine structure EXAFS at the Zn and Se K-edge in order to determine the bulk and bond-specific elastic properties. Our measurements on samples with x =0.06–0.55 show pressure induced phase transformation from zinc blende to NaCl. The phase transformation pressure increases linearly with x. Murnaghan equation of state fitting to the data yields the unit cell volume at ambient pressure and bulk modulus, both of which follow the Vegard's law. Nearest neighbor bond distances derived from EXAFS do not show sharp phase transition except for x=0.06. Bond modulus derived for the Zn–Se bonds shows them to be apparently stiffer than the bulk alloy, which is nontrivial. This tendency increases with increasing x and a strong positive bowing from the Vegard's law is observed. We attribute the observed anomalies to the contrastingly different properties of the two components ZnSe and BeSe