Crystal chemistry, stoichiometry, and electrical and magnetic properties of phases of the FeNb3Se10structure type

We have found the true stoichiometry of the phase first reported as ${\mathrm{Fe}}_{0.25}$ ${\mathrm{Nb}}_{0.75}$ ${\mathrm{Se}}_{12}$, and later as Fe${\mathrm{Nb}}_3$ ${\mathrm{Se}}_{10}$, to be ${\mathrm{Fe}}_{1+x}{\mathrm{Nb}}_{3-x}{\mathrm{Se}}_{10}$, with $0.25\le x\le 0.40$. Compounds with the Fe${\mathrm{Nb}}_3$ ${\mathrm{Se}}_{10}$ structure type are relatively rare among transition-metal selenides. We report the synthesis and temperature-dependent magnetic susceptibility and resistivity of the new compounds ${\mathrm{Fe}}_{1.33}$ ${\mathrm{Ta}}_{0.67}$ ${\mathrm{Nb}}_2$ ${\mathrm{Se}}_{10}$ and ${\mathrm{Fe}}_{1-y}{\mathrm{V}}_{1+y}{\mathrm{Nb}}_2{\mathrm{Se}}_{10}$, with $0.0\le y\le 0.5$. The magnetic susceptibility and Mössbauer-effect measurements on ${\mathrm{Fe}}_{1+x}{\mathrm{Nb}}_{3-x}{\mathrm{Se}}_{10}$ are dominated by the Fe-Nb disorder on the zigzag octahedral chains.