Single-crystal structures, optical absorptions, and electronic distributions of thorium oxychalcogenides ThOQ (Q = S, Se, Te)

Transport and topological properties of ThOCh(Ch: S, Se and Te) in bulk and monolayer: a first principles study

The present study unveils the topological insulating nature of Th-based oxy-chalcogenides and their transport properties which are less explored. A systematic analysis of electronic, topological, mechanical, dynamical and thermoelectric properties of ThOCh (Ch: S, Se and Te) in bulk and monolayer is presented. The effect of spin-orbit coupling is found to be appreciable in ThOTe compared to ThOS and ThOSe, causing a strong topological nature in bulk ThOTe. The detailed analysis of electronic structure, Z₂ topological invariant and conducting surface states support the strong topological nature in bulk ThOTe. From thermoelectric studies, ThOS and ThOSe are found to be good thermoelectric candidates with heavy carrier doping (around 10²⁰ cm^-3). To explore further, we have applied hydrostatic strain on bulk ThOCh and found that all the compounds are dynamically stable and show topological metallic behavior. The appearance of highly linearized Dirac points in the same energy range at different high symmetry points in the BZ indicate the presence of nodal line in ThOS and ThOSe without spin-orbit coupling and with the inclusion of spin-orbit coupling, the nodal line is found to be disappear. This variation in bands with and without spin-orbit coupling might indicate the topological nature in monolayer ThOCh. The thermoelectric calculations for monolayer shows an enhancement in electrical conductivity scaled by relaxation time by an order of ten compared to bulk and the carrier independent thermoelectric properties in monolayer might fetch good thermoelectric device applications. Overall, the present study explores yet another series of potential candidates for topological and thermoelectric properties in both bulk and layer forms.

Pressure-induced structural transformations and polymerization in ThC2

Thorium-carbon systems have been thought as promising nuclear fuel for Generation IV reactors which require high-burnup and safe nuclear fuel. Existing knowledge on thorium carbides under extreme condition remains insufficient and some is controversial due to limited studies. Here we systematically predict all stable structures of thorium dicarbide (ThC₂) under the pressure ranging from ambient to 300 GPa by merging ab initio total energy calculations and unbiased structure searching method, which are in sequence of C2/c, C2/m, Cmmm, Immm and P6/mmm phases. Among these phases, the C2/m is successfully observed for the first time via in situ synchrotron XRD measurements, which exhibits an excellent structural correspondence to our theoretical predictions. The transition sequence and the critical pressures are predicted. The calculated results also reveal the polymerization behaviors of the carbon atoms and the corresponding characteristic C-C bonding under various pressures. Our work provides key information on the fundamental material behavior and insights into the underlying mechanisms that lay the foundation for further exploration and application of ThC₂.

Overview of the crystal chemistry of the actinide chalcogenides: incorporation of the alkaline-earth elements

This review focuses on the results of exploratory syntheses of alkaline-earth-metal actinide chalcogenides Ak–An–Q (Ak = Ba, Sr; An = Th, U; Q = S, Se, and Te). About thirty new compounds and eleven new structure types are described.

The flexible Ba7UM2S12.5O0.5 (M = V, Fe) compounds: syntheses, structures and spectroscopic, resistivity, and electronic properties

Two new compounds, Ba7UV2S12.5O0.5 and Ba7UFe2S12.5O0.5, have been synthesized in fused-silica tubes by the direct combinations of V or Fe with U, BaS, and S at 1223 K. The compound Ba7UV2S12.5O0.5 crystallizes at 100 K in the Cs7Cd3Br17 structure type in space group D4h(18)–I4/mcm of the tetragonal system. The compound Ba7UFe2S12.5O0.5 crystallizes at 100 K in space group D4h(5)–P4/mbm of the tetragonal system. The structures are very similar with V/S or Fe/S networks in which Ba atoms reside as well as channels large enough to accommodate additional Ba atoms and infinite linear US5O chains. Each U atom is octahedrally coordinated to four equatorial S atoms, one axial S atom, and one axial O atom. The Fe/S network contains a S–S single bond, whereas the V/S network does not. The result is that the Fe3+ compound charge balances with 7 Ba2+, U4+, 2 Fe3+, 10.5 S2–, S2(2–), and 0.5 O2–, whereas the V4+ compound charge balances with 7 Ba2+, U4+, 2 V4+, 12.5 S2–, and 0.5 O2–. Other differences between these two compounds have been characterized by Raman spectroscopy and resistivity measurements. DFT calculations have provided insight into the nature of their bonding. The overall structural motif of Ba7UV2S12.5O0.5 and Ba7UFe2S12.5O0.5 offers a remarkable flexibility in terms of the oxidation state of the incorporated transition metal.