Compressibility, Metallization, and Relaxation in Nonstoichiometric Chalcogenide Glass g-As3Te2 at High Hydrostatic Pressure versus “Classic” g-As2Te3 Glass

Abstract

The volume and conductivity of nonstoichiometric chalcogenide glass g-As3Te2 have been investigated at high hydrostatic pressures (up to 8.5 GPa), and results have been compared with earlier data for stoichiometric chalcogenide glass g-As2Te3. Structural and Raman studies of g-As3Te2 glass have revealed a greater significance of As–As pair correlations in the range of medium-range order compared with “classic” chalcogenide glass g-As2Te3. Even at such a large excess of arsenic, a high concentration of “improper” Te–Te neighbors has been observed because of chemical disorder. Under normal conditions, the thermal gap (0.43–0.48 eV) and resistivity (104 Ω cm) of glass g-As3Te2 are greater than those of g-As2Te3. The elastic behavior of g-As3Te2 glass, as well as of g-As2Te3, under compression has been observed at pressures up to 1 GPa, the initial values of bulk moduli for these glasses being nearly coincident. Polyamorphic transformation in g-As3Te2 (with softening of relaxing bulk modulus) is more diffuse and extends to higher pressures (from 1.5 to 4.0 GPa). The metallization process in g-As3Te2 is also more diffuse: metallic conductivity is reached at pressures of 5.5–6.0 GPa. As in the case of the stoichiometric glass, the baric dependences of the bulk modulus exhibit a kink in the pressure range 4–5 GPa. Up to maximal pressures, the volume and resistivity relax logarithmically in time with roughly the same rate as in the case of g-As2Te3. The residual densification of g-As3Te2 after pressure release is roughly twice as high as for g-As2Te3 and equals 3.5%, the conductivity of the compacted glass is about three orders of magnitude higher than that of the as-prepared sample. Under normal conditions, a considerable relaxation of the volume and resistivity has been observed. As for densified g-GeS2 glass, the logarithmic kinetics of this relaxation has been successfully described in terms of our earlier model based on the concept of relaxation self-organized criticality with the activation energy (1.3 eV) remaining unchanged up to 5 × 106 s.