Syntheses and Structures of Some Low-Dimensional Rare-Earth Tellurides

Abstract

In this study, the following two methods were introduced in an attempt to synthesize low-dimensional rare earth tellurides. 1) Chloride flux method 2) Chalcogenide flux method In the first part, a series of awempts to synthesize new ternary alkali metal - rare earth - chalcogenides were carried out. However only binary phases could be obtained instead of ternary compounds except except NaErTe_(2). In th Cs-R-Te sysem, only YbTe and Er_(2)Te_(3) were produced. In the Rb-R-Te system, only Rb_(2)Te_(5) and YbTe were obtained. In the Li-R-Te system, Li_(2)Te was produced. In the Na-R-Te system, YbTe, ErTe and air-sensitive transparent red crystal NaErTe_(2) were obtained. From single crystal X-ray diffraction study, the cell parameters of red crystal obtained were a=4.354Å, b=4.341Å, c=22.45Å, α=90˚, β=90˚, γ=120˚. This structure is NaFeO_(2)-thpe and isotructural of NaSmTe_(2). From this study, we found that the probability to obtain novel ternary tellurides is low relative to simple binary tellurides at high temperature in chloride flux. The propensity to be NaFeO_(2)-structure become stronger extending from sulfides, selenides to tellurides. The latter is from the fact that the bigger the anionic radius of chalcogen, the harder the cation move through anionic layer at the above T_t high temperature reaction. In the second part, the synthetic route was extended to chalcogenide flux method to obtain metastable and kinetically controlled new ternary tellurides. In the K-Er-Te system, only Te single crystals were abtained. In the K-Y-Te system, red single crystals were abtained. From EDAX analysis, we found that the composition of this red crystal is K:Y:Te=22:27:45. From single crystal X-ray diffraction experiment, the cell parameters obtained were a=3.73Å, b=3.73Å, c=5.40Å, α=108˚, β=106˚, γ=98.7˚. Further structural refinement on this crystal is under way. In the K-Ce-Te system, yellow hexagonal single crystals were obtained. From EDAX analysis, we found that the composition of yellow crystal is K:Ce:Te+1:3:10. The cell parameters were a=9.01Å, b=12.97Å, c=27.2Å, α=89.98˚, β=99.20˚, γ=90.03˚. Data collection on this crystal is under way. In K-Nd-Te, K-Gd-Te, K-Eu-Te, K-La-Te and K-Sm-Te system many single crystals were observed, so single crystal X-ray diffraction analysis will be done. From these crystals, new ternary tellurides are expected to be found. From this study, we found that in the K_2Te/Te flux the reactivity to tellurium of Nd, Gd, Eu, La, Sm and Ce is higher than that of Y Yb, Pr and Er, and proper reaction temperature is higher than 440℃.