Preparation, Properties and Crystal Structure of I_<0.5>TaSe_4(EXPERIMENTS ON (MX_4)_nY COMPOUNDS, International Symposium on NONLINEAR TRANSPORT AND RELATED PHENOMENA IN INORGANIC QUASI ONE DIMENSIONAL CONDUCTORS)

Abstract

I_<0.5>TaSe_4 was obtained by heating the starting mixture having compositional ratio of Se/Ta=4 and I/Ta=1 in 460℃/420℃ temperature gradient for 1 week. The compound was tetragonal having lattice parameters a=9.555Å and c=12.75Å. The observed density was 5.99 g/cm^3. X-ray structural analysis showed that tantalum is coordinated with 4 Se-Se dimers forming [TaSe_4] infinit chain along c-axis. Iodine is located between the chain. There are two kinds of tantalum in the chain. The short distance of 3.24Å between Se and I suggests that iodine is partially transfered electrons from every two Ta through Se. The electrical resistivity along c-axis was 1.9 x 10^3 Ωcm at room temperature and the activation energy was 0.06 eV. Magnetic susceptibility showed very weak temperature dependence; -1.7 x 10^<-7> emu/g at room temperature and -1.7 x 10^<-8> emu/g at 77K. The presences of Ta^<4+>, Ta^<5+> and (Se-Se)^<2-> were observed on X-ray photoelectron spectrum comparing with those of TaSe_2, TaSe_3 and Ta_2O_5.