Preparation and characterization of compounds of the system FeAs2−xSex

High-pressure MnP4, a polyphosphide with Mn–Mn pairs

“…* The present model differs from the one proposed by Goodenough (1972) mainly in the relative position of bonding and nonbonding tza levels above and below the Fermi level. Thus conductive and magnetic properties are similar for both models and our model agrees well with the experimental findings for FeAs2, FeSb2 (Fan, Rosenthal, McKinzie & Wold, 1972), and FeAsz_xSex (Baghdadi & Wold, 1974).…”

Measured and simulated thermoelectric properties of FeAs2−xSex (x = 0.30–1.0): from marcasite to arsenopyrite structure

“…The valence orbitals are comprised of two degenerate 'b' bonding orbitals, a nonbonding 'a ll ' orbital, and two anti-bonding 'a' orbitals which originate from Fe's 3d orbitals mixing with As's orbitals. FeAs 2 is stable in the marcasite structure because the b orbitals are fully filled, but when Se or Te is substituted for As the extra electron begins to populate the a ll orbital which adds a destabilizing effect that the structure can compensate until x = 0.8 in the Te system 10 and B0.65 in the Se system.…”

“…Wold et al have shown that FeAs 2 can be alloyed with Se. 10 The solid solution of FeAs 2Àx Se x (x = 0, 0.06, 0.13) was synthesized. For every Se substituted with As, one extra electron is added to the system and the carrier concentration increases therefore decreasing the Seebeck coefficient (À200 mV K À1 , À59 mV K À1 , À39 mV K À1 ).…”

“…For every Se substituted with As, one extra electron is added to the system and the carrier concentration increases therefore decreasing the Seebeck coefficient (À200 mV K À1 , À59 mV K À1 , À39 mV K À1 ). 10 The iron dichalcogenides (FeX 2 , X = S, Se, Te) have also been synthesized. FeS 2 crystallizes in the cubic pyrite (Pa3) structure, while FeSe 2 and FeTe 2 crystallize in the marcasite structure (Pnnm).…”

Relating Electron Configuration, Crystal Structure and Band Structure

“…The system (Cr/Mn)02148though without the pairing problem again shows differentiation of site, Cr 3 +/Mn S +, and as expected a rapid loss of conductivity. Pure Mn02 is a Mott insulator, as in d3Cr203' Cr-doping indeed rapidly renders V203 insulating (1% at 300 0 K)" 40. However from what we have seen this system cannot (even at this low doping level) provide the ideal test system to monitor the Mott transition, especially since in the corundum structure the V atoms at the transition take advantage of the fact that their c-axis position is not a special point.…”