Twofold Chain Structure Research Articles

Short range structures of amorphous Se–Te prepared by mechanical alloying

The time-of-flight neutron scattering measurement was employed in order to elucidate the short range structures for a series of amorphous Se 100− x Te x ( x=0∼20) mixtures synthesized by mechanical alloying (MA). The first peak in the radial distribution functions was resolved into two Gaussian peaks, which correspond to the Se–Se and Se–Te correlations, respectively. Amorphous Se prepared by MA has a lot of dangling bonds. In contrast, for the Se 100− x Te x samples, Te atoms are preferentially bonded with the dangling bonds of Se atoms with increasing Te concentration and, consequently, a twofold chain structure is formed.

ＭＡにより作製したアモルファスＳｅ‐Ｔｅの中性子回折

Amorphous Se100-xTex powders (x=0, 5, 10, 15 and 20) have been produced by mechanical alloying (MA). The time-of-flight neutron scattering measurement was employed in order to elucidate the short range structures for these powders. Well-resolved first peak in radial distribution functions can be decomposed into two Gaussian peaks, which correspond to the Se-Se and Se-Te correlation. The coordination number teaches us that amorphous Se has a lot of dangling bonds due to broken of Se-Se bond by milling. However, the compositional changes of the coordination numbers of Se-Se and Se-Te pairs for Se-Te powders imply that Te atoms are bonded to the edge of Se chain molecules and the twofold chain structure is built up with increasing Te content.

EXAFS study on liquid selenium and liquid tellurium under high pressure

Extended X-ray absorption fine structure (EXAFS) measurements were performed on crystalline and liquid Se at 2.5 GPa. A decrease of amplitude of the EXAFS oscillation for liquid Se was observed at temperatures >1050 K. The decrease was larger than that expected from the normal thermal effect and it indicates that the two-fold chain structure in liquid Se is modified at temperatures >1050 K. The change occurs near the boundary of a semiconductor-to-metal transition. This coincidence confirms that the transition is accompanied by a structural change. EXAFS for crystalline and liquid Te at 6 GPa were also measured. The peak amplitude in radial distribution function for liquid Te at 6 GPa is smaller than that observed at the similar temperature and atmospheric pressure. We suggest that the decrease is due to the modification of the covalent bonds.