%APerez, Christopher%ADevlin, Kasey%ASkaggs, Callista%ATan, Xiaoyan%AFrank, Corey%ABadger, Jackson%AKang, Chang-Jong%AEmge, Thomas%AKauzlarich, Susan%ATaufour, Valentin%AKotliar, Gabriel%ALapidus, Saul%AGreenblatt, Martha%Anull Ed.%BJournal Name: Materials Advances; Journal Volume: 1; Journal Issue: 5 %D2020%I %JJournal Name: Materials Advances; Journal Volume: 1; Journal Issue: 5 %K %MOSTI ID: 10249778 %PMedium: X %TMeasured and simulated thermoelectric properties of FeAs 2−x Se x ( x = 0.30–1.0): from marcasite to arsenopyrite structure %XFeAs 2−x Se x ( x = 0.30–1.0) samples were synthesized as phase pure powders by conventional solid-state techniques and as single crystals ( x = 0.50) from chemical vapor transport. The composition of the crystals was determined to be Fe 1.025(3) As 1.55(3) Se 0.42(3) , crystallizing in the marcasite structure type, Pnnm space group. FeAs 2−x Se x (0 < x < 1) was found to undergo a marcasite-to-arsenopyrite ( P 2 1 / c space group) structural phase transition at x ∼ 0.65. The structures are similar, with the marcasite structure best described as a solid solution of As/Se, whereas the arsenopyrite has ordered anion sites. Magnetic susceptibility and thermoelectric property measurements from 300–2 K were performed on single crystals, FeAs 1.50 Se 0.50 . Paramagnetic behavior is observed from 300 to 17 K and a Seebeck coefficient of −33 μV K −1 , an electrical resistivity of 4.07 mΩ cm, and a very low κ l of 0.22 W m −1 K −1 at 300 K are observed. In order to determine the impact of the structural transition on the high-temperature thermoelectric properties, polycrystalline FeAs 2−x Se x ( x = 0.30, 0.75, 0.85, 1.0) samples were consolidated into dense pellets for measurements of thermoelectric properties. The x = 0.85 sample shows the best thermoelectric performance. The electronic structure of FeAsSe was calculated with DFT and transport properties were approximately modeled above 500 K. %0Journal Article