Occurrence of the neotropical moss Dicranella hilariana (Mont.) Mitt. in the Antarctic

Dicranella hilariana (Mont.) Mitt., a pan-neotropical moss species, is reported for the first time from the Antarctic botanical zone. It was found on geothermally heated ground near fumaroles on Visokoi, Candlemas and Bellingshausen Islands in the volcanic archipelago of the South Sandwich Islands. Dicranella recurvata Ochyra, Arts & Lewis-Smith, nom. nud., is reduced to synonymy with D. hilariana. The Antarctic plants of D. hilariana are briefly described and illustrated, including the rhizoidal tubers which have not previously been reported in this species. The global distribution of D. hilariana is briefly reviewed and mapped. It is suggested that the species reached the Antarctic via long-distance dispersal from South America by the prevailing strong westerly winds

Metal Distributions, Efficient n-Type Doping, and Evidence for in-Gap States in TiNiM_<i>y</i>Sn (M = Co, Ni, Cu) half-Heusler Nanocomposites

XNi1+ySn nanocomposites consisting of a XNiSn half-Heusler (HH) matrix with segregated XNi2Sn Full Heusler (FH) inclusions promise improvements in thermoelectric efficiencies. We extend recent research by reporting on TiNiMySn (0 ≤ y ≤ 1) nanocomposites with M = Co (3d9), Ni (3d10) and Cu (3d104s1). Neutron powder diffraction reveals that the Ni and Cu series produce a matrix of TiNiSn with nanosegregated TiNi2Sn and TiNi1+dCu1–dSn, respectively. For the Co series, the Co inserts into both phases to obtain a TiNi1–yCoySn matrix with nanosegregated TiNi2–yCoySn. Systematic changes in Seebeck coefficient (S) and electrical resistivity (ρ) are observed in all three series. For M = Ni, changes in S and ρ are attributed to in-gap states arising from the nanosegregation. The M = Co composites show a complex interplay between the hole doped TiNi1–yCoySn matrix and similar in-gap states, where the p- to n-type transition temperature increases but the maximum S remains unchanged at +30 μV K–1. The 4s1 electron for M = Cu is delocalized in the HH matrix, leading to metal-like ρ(T) and up to 100% improved thermoelectric power factors compared to TiNiSn (S2/ρ = 2 mW m–1 K–2 at 600–700 K for y = 0.025). These results broaden the range of segregated FH phases that could be used to enhance HH thermoelectric performance

Four additional lichens from the Antarctic and South Georgia, including a new Leciophysma species

Four lichen species new to the Antarctic and sub-Antarctic South Georgia are reported. One is new to science: a species of Leciophysma with rough, non-granular thallus and reduced proper exciple. A total of 484 lichenized fungal taxa have now been reported from Antarctica and South Georgia.

Enhanced Oxygen Ion Conductivity and Mechanistic Understanding in Ba3Nb1-xVxMoO8.5

Funding Sources This research was supported by the Leverhulme trust and the University of Aberdeen. ACKNOWLEDGMENT We also acknowledge STFC-GB for provision of beamtime at ISIS.Peer reviewedPostprin

Impact of Nb vacancies and p-type doping of the NbCoSn-NbCoSb half-Heusler thermoelectrics

Nb vacancies maintain a semiconducting electron count and cause strong mass fluctuation phonon scattering enabling good thermoelectric performance.</p

The impact of manganese substitution on the structure and properties of tetrahedrite

The crystal structure of the tetrahedrites Cu12-xMnxSb4S13 (x = 0, 1) has been studied by powder neutron diffraction between room temperature and 773 K. At all temperatures investigated, manganese exclusively occupies tetrahedral sites, while the trigonal-planar sites contain only copper. In situ diffraction data confirm the stability of the tetrahedrite phase up to 773 K, with no evidence of copper mobility at elevated temperatures. Analysis of atomic displacement parameters indicate that there are low-energy vibrations associated with the trigonal-planar and the tetrahedral copper cations. The Einstein temperatures for the copper cations range between 79 and 91 K. Manganese substitution increases the electrical resistivity and the Seebeck coefficient, while the thermal conductivity is reduced. This results in a modest improvement in the thermoelectric figure of merit for Cu12MnSb4S13, which reaches ZT=0.56 at 573 K

Order-disorder and ionic conductivity in calcium nitride-hydride

Prof John TS Irvine and Prof Martin Owen Jones: STFC 5005—Development of Combined In situ Neutron Diffraction and Electrochemical Studies.Recently nitrogen-hydrogen compounds have successfully been applied as co-catalysts for mild conditions ammonia synthesis. Ca2NH was shown to act as a H2 sink during reaction, with H atoms from its lattice being incorporated into the NH3(g) product. Thus the ionic transport and diffusion properties of the N–H co-catalyst are fundamentally important to understanding and developing such syntheses. Here we show hydride ion conduction in these materials. Two distinct calcium nitride-hydride Ca2NH phases, prepared via different synthetic paths are found to show dramatically different properties. One phase (β) shows fast hydride ionic conduction properties (0.08 S/cm at 600 °C), on a par with the best binary ionic hydrides and 10 times higher than CaH2, whilst the other (α) is 100 times less conductive. An in situ combined analysis techniques reveals that the effective β-phase conducts ions via a vacancy-mediated phenomenon in which the charge carrier concentration is dependent on the ion concentration in the secondary site and by extension the vacancy concentration in the main site.Publisher PDFPeer reviewe

The effect of electron and hole doping on the thermoelectric properties of shandite-type Co3Sn2S2

Electron and hole doping in Co3Sn2S2, through chemical substitution of cobalt by the neighbouring elements, nickel and iron, affects both the structure and thermoelectric properties. Electron doping to form Co3-xNixSn2S2 (0 ≤ x ≤ 3) results in an expansion of the kagome layer and materials become increasingly metallic as cobalt is substituted. Conversely, hole doping in Co3-xFexSn2S2 (0 ≤ x ≤ 0.6) leads to a transition from metallic to n-type semiconducting behaviour at x = 0.5. Iron substitution induces a small increase in the separation between the kagome layers and improves the thermoelectric performance. Neutron diffraction data reveal that substitution occurs at the Co 9(d) site in a disordered fashion. Mössbauer spectroscopy reveals two iron environments with very different isomer shifts, which may be indicative of a mixed-valence state, while Sn exhibits an oxidation state close to zero in both series. Co2.6Fe0.4Sn2S2 exhibits a maximum figure-of-merit, ZT = 0.2 at 523 K while Co2.4Fe0.6Sn2S2 reaches a power factor of 10.3 μW cm-1 K-2 close to room temperature