Transport properties of some derivatives of tetrathiafulvalene-tetracyano-p-quinodimethane (TTF-TCNQ)

Abstract

Data on dc conductivity $\sigma \mathrm{}\left(T\right)\mathrm{}$ and thermoelectric power $S\left(T\right)\mathrm{}$ for four organic conductors related to tetrathiafulvalene-tetracyano-$p$-quinodimethane (TTF-TCNQ) are presented. They all qualitatively behave as TTF-TCNQ with metal-insulator ($M-I$) transitions at temperatures around 50 K. Tetramethyltetraselenafulvalene-tetracyano-$p$-quinodimethane (TMTSeF-TCNQ) has $\sigma \left(300\mathrm{} \mathrm{K}\right)=1000\mathrm{}$ ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\frac{{\sigma }_{max}}{\sigma \left(300\mathrm{} \mathrm{K}\right)}=7\mathrm{}$, $S\left(300\mathrm{} \mathrm{K}\right)=8\mathrm{}\mu \mathrm{V}/\mathrm{K}$. For tetramethyltetraselenafulvalene-dimethyltetracyano-$p$-quinodimethane (TMTSeF-DMTCNQ) $\sigma \left(300\mathrm{} \mathrm{K}\right)=500\mathrm{}$ ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\frac{{\sigma }_{max}}{\sigma \left(300\mathrm{} \mathrm{K}\right)}=10\mathrm{}$, $S\left(300\mathrm{} \mathrm{K}\right)=11\mathrm{}$ μV/K. The sulphur analogue tetramethyltetrathiafulvalene-dimethyltetracyano-$p$-quinodimethane (TMTTF-DMTCNQ) has $\sigma \left(300\mathrm{} \mathrm{K}\right)=120\mathrm{}$ ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\frac{{\sigma }_{max}}{\sigma \left(300\mathrm{} \mathrm{K}\right)}=3\mathrm{}$, $S\left(300\mathrm{} \mathrm{K}\right)=-30\mathrm{}$ μV/K, while for diethyldimethyltetraselenafulvalene-tetracyano-$p$-quinodimethane (DEDMTSeF-TCNQ) we find $\sigma \left(300\mathrm{} \mathrm{K}\right)=500\mathrm{}$ ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\frac{{\sigma }_{max}}{\sigma \left(300\mathrm{} \mathrm{K}\right)}=9\mathrm{}$,

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