Metal Substitution Effects on the Charge Transport and Spin Crossover Properties of [Fe_1–xZn_x(Htrz)₂(trz)](BF₄) (trz = Triazole)

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 13962To link to this article :ABSTRACT: In this study we analyze the metal substitution effects on the structural, morphological, charge transport, and spin transition properties of the [Fe 1−x Zn x (Htrz) 2 (trz)](BF 4 ) (trz = triazole, x = 0, 0.26, or 0.43) compound using electron microscopy, powder X-ray diffraction, optical reflectivity, Raman, FTIR, 57 Fe Mossbauer, and broadband (10 −2 −10 6 Hz) dielectric spectroscopies. The crystal structure and the morphology of the objects remain nearly unaffected, whereas the thermal spin transition shifts from 362 to 316 K and the thermal hysteresis width decreases from 45 to 8 K for increasing values of x. For each compound the electrical conductivity drops when the iron(II) electronic configuration is switched from the low-spin to the high-spin state. A strong overall decrease in conductivity with increasing Zn concentration is also observed in both spin states. These results, together with the analysis of the charge carrier dynamics, suggest that the ferrous ions participate directly in the charge transport mechanism, explaining the strong spin-state dependence of the electrical properties in this compound.

Ligand substitution effects on the charge transport properties of the spin crossover complex [Fe(Htrz)1+y−x (trz)2−y (NH2trz) x ](BF4)y·nH2O

“…This means that the electron-phonon coupling at the origin of the hopping charge transport must involve primarily optical modes of the coordination chain [Fe(Htrz) 2 (trz)] n n+ . This result comes to support our previous hypothesis [15] that the charge transport in this compound takes place primarily by carrier hopping between the iron ions along the chains. All these results point thus to the importance of the dimensionality (1D) of this compound in the charge transport properties.…”

“…phonon) frequencies when going from the LS to the HS state. Remarkably, the room temperature conductance of [Fe 1−x Zn x (Htrz) 2 (trz)](BF 4 ) solid solutions dropped by seven orders of magnitude for a ca 43% substitution of the open shell (3d 6 ) Fe(II) ions by closed shell (3d 10 ) Zn(II) ions [15]. This result indicates that the iron atoms are directly involved in the hopping charge transport, which can-in part-explain also the relatively large variation of the conductivity upon the SCO in this compound.…”

Electrical conductivity and magnetic bistability in metal–organic frameworks and coordination polymers: charge transport and spin crossover at the nanoscale

“…254 Bousseksou, Salmon and co-workers performed most of the work with this material (Figure 13). [255][256][257][258][259][260] These different studies were performed with different set-ups (two probe contacts or interdigitated electrodes, 259,260 DC 258 or AC conductivities 255,261,257 ) and using samples with slightly different crystallite sizes (0.7-5 µm x 200-300 nm high aspect ratio needles [258][259][260] or ~200 nm nearly spherical particles 255,261,257,258 ) and large electrode gaps of several micrometres. Nonetheless, most of them yielded comparable results and pointed to the same conclusion: the HS form is less conductive than the LS state (Figure 13b).…”

Charge Transport and Electrical Properties of Spin Crossover Materials: Towards Nanoelectronic and Spintronic Devices

“…A very significant increase of these characteristic frequencies was observed when going from the HS to the LS state providing thus experimental evidence for the higher hopping frequencies in the LS state. The electrical properties of the [Fe 1´x Zn x (Htrz) 2 (trz)](BF 4 ) Zn-diluted series were also investigated [39]. The conductivity of the diluted compounds decreased with 3 (x = 0.26) and 6 (x = 0.43) orders of magnitude, suggesting that the iron ions participate directly in the charge transport process.…”