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[摘要]：We report here the substitution of Se by Te in the Mott insulator GaTa(4)Se(8-y)Te(y) a lacunar spinet compound containing Ta(4) tetrahedral clusters. Our synthetic and crystallographic works show that Te atoms occupy successively two different crystallographic sites and that the substitution reaches a limit for GaTa(4)Se(1.5)Te(6.5). Band structure calculations and transport measurements demonstrate that this substitution induces for low Te doping (0 <= y <= 4) an increase of the band gap related to a narrowing of the d bands (i.e., a negative chemical pressure effect). Conversely, for higher Te doping (y >= 4), a decrease of the band gap is observed, while the bandwidth of the d bands stays almost constant. This result suggests that the partial declusterization of Ta4 tetrahedra observed at high Te doping (y >= 4) leads to a very unusual reduction of the electronic repulsion energy (U) that opens the gap between the lower and upper Hubbard bands. The GaTa(4)Se(8-y)Te(y) compounds therefore provide, to our knowledge, the first example of a U-controlled tuning of electronic properties in a Mott insulator. Moreover, we show that the substitution of Se by Te GaTa(4)Se(8-y)Te(y) does not affect drastically the reversible and nonvolatile electric pulse-induced resistive switching phenomena discovered recently in the nonsubstituted compound GaTa(4)Se(8). |
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