In this review, we describe the creation of a large database of thermoelectric materials prepared by abstracting information from over 100 publications. The database has over 18 000 data points from multiple classes of compounds, whose relevant properties have been measured at several temperatures. Appropriate visualization of the data immediately allows certain insights to be gained with regard to the property space of plausible thermoelectric materials. Of particular note is that any candidate material needs to display an electrical resistivity value that is close to 1 mW cm at 300 K, i.e., samples should be significantly more conductive than the Mott minimum metallic conductivity. The Herfindahl-Hirschman index, a commonly accepted measure of market concentration, has been calculated from geological data (known elemental reserves) and geopolitical data (elemental production) for much of the periodic table. The visualization strategy employed here allows rapid sorting of thermoelectric compositions with respect to important issues of elemental scarcity and supply risk.

We report the novel preparation of single crystals of tetragonal iron sulfide, FeS, which exhibits a nearly ideal tetrahedral geometry with S-Fe-S bond angles of 110.2(2) • and 108.1(2) • . Grown via hydrothermal de-intercalation of KxFe2−yS2 crystals under basic and reducing conditions, the silver, plate-like crystals of FeS remain stable up to 200 • C under air and 250 • C under inert conditions, even though the mineral "mackinawite" (FeS) is known to be metastable. FeS single crystals exhibit a superconducting state below Tc = 4 K as determined by electrical resistivity, magnetic susceptibility, and heat capacity measurements, confirming the presence of a bulk superconducting state. Normal state measurements yield an electronic specific heat of 5 mJ/mol-K 2 , and paramagnetic, metallic behavior with a low residual resistivity of 250 µΩ·cm. Magnetoresistance measurements performed as a function of magnetic field angle tilted toward both transverse and longitudinal orientations with respect to the applied current reveal remarkable two-dimensional behavior. This is paralleled in the superconducting state, which exhibits the largest known upper critical field Hc2 anisotropy of all iron-based superconductors, with H ||ab c2 (0)/H ||c c2 (0) =(2.75 T)/(0.275 T)=10. Comparisons to theoretical models for 2D and anisotropic-3D superconductors, however, suggest that FeS is the latter case with a large effective mass anisotropy. We place FeS in context to other closely related iron-based superconductors and discuss the role of structural parameters such as anion height on superconductivity.

A novel cerium-substituted, barium yttrium silicate has been identified as an efficient blue-green phosphor for application in solid state lighting. Ba9Y2Si6O24:Ce(3+) was prepared and structurally characterized using synchrotron X-ray powder diffraction. The photoluminescent characterization identified a major peak at 394 nm in the excitation spectrum, making this material viable for near-UV LED excitation. An efficient emission, with a quantum yield of ≈60%, covers a broad portion (430-675 nm) of the visible spectrum, leading to the blue-green color. Concentration quenching occurs when the Ce(3+) content exceeds ≈3 mol %, whereas high temperature photoluminescent measurements show a 25% drop from the room temperature efficiency at 500 K. The emission of this compound can be red-shifted via the solid solution Ba9(Y(1-y)Sc(y))(1.94)Ce(0.06)Si6O24 (y = 0.1, 0.2), allowing for tunable color properties when device integration is considered.

We report the phase diagram for the superconducting system (7Li1−xFexOD)FeSe and contrast it with that of (Li1−xFexOH)FeSe both in single crystal and powder forms.

Neutron diffraction and small angle scattering experiments have been carried out on the doubleisotopic polycrystalline sample ( 7 Li 0.82 Fe 0.18 OD)FeSe. Profile refinements of the diffraction data establish the composition and reveal an essentially single phase material with lattice parameters of a= 3.7827 Å and c= 9.1277 Å at 4 K, in the ferromagnetic-superconductor regime, with a bulk superconducting transition of T C = 18 K. Small angle neutron scattering (SANS) measurements in zero applied field reveal the onset of ferromagnetic order below T F ≈ 12.5 K, with a wave vector and temperature dependence consistent with an inhomogeneous ferromagnet of spontaneous vortices or domains in a mixed state. No oscillatory long range ordered magnetic state is observed. Field dependent measurements establish a separate component of magnetic scattering from the vortex lattice, which occurs at the expected wave vector. The temperature dependence of the vortex scattering does not indicate any contribution from the ferromagnetism, consistent with diffraction data that indicate that the ordered ferromagnetic moment is quite small. PACS: 74.70.Xa, 74.25.Ha, 75.25.Uv; 75.25.-j *corresponding author. Jeffrey.Lynn@nist.gov 2 The magnetic properties of superconductors have a rich and interesting history. Early work showed that even tiny concentrations of magnetic impurities destroyed the superconducting pairing through the exchange-driven spin depairing mechanism, prohibiting any possibility of cooperative magnetic behavior.[1] The first exception to this rule was provided by the cubic rare-earth substituted CeRu 2 alloys [2][3][4], while the ternary Chevrel-phase (and related) superconductors (e.g. RMo 6 S 8 , R=rare earth) provided the first demonstrations of long range magnetic order coexisting with superconductivity. [5,6] The magnetic ordering temperatures were all quite low (~1 K), where electromagnetic (dipolar + London penetration depth) interactions play a dominate role in the energetics of the magnetic system. The vast majority of these materials order antiferromagnetically where coexistence of long range order with superconductivity was common, but these materials also provided the first examples of the rare occurrence of ferromagnetism and consequent competition with superconductivity in ErRh 4 B 4 , [7][8][9][10] HoMo 6 S 8 , [11][12][13] and HoMo 6 Se 8 .[14] Antiferromagnetic order is found for all the rare earths in the cuprates, which exhibit similar low ordering temperatures. [15] In the borocarbide superconductors again of all the magnetic order is antiferromagnetic, [16] with the singular exception of ErNi 2 B 2 C at low temperature [17,18] where a net magnetization developed that resulted in the spontaneous formation of flux quanta (vortices). [19,20] For the high-T C superconductors of direct interest here, there have been no ferromagnets in either the cuprate or iron-based systems, [15,[21][22][23] [28] For this latter system T C can be as high as 43 K, together with the development of magnetic ord...