Electrical conductivity and crystallization kinetics in Te-Se glassy system

Abstract

Non-isothermal measurements of dc conductivity were used to study crystallization in bulk glasses from the TexSe100−x system (x = 10, 20, and 30). In combination with infrared microscopy, it provides a very good qualitative picture of the complex crystallization processes, as the formation of conductive paths proceeds more or less separately for each involved process. In addition, due to the pronounced signal corresponding to the surface crystallization, the dc conductivity measurements seem to bear great potential for crystallization kinetic studies. Based on identified characteristic states corresponding to the particular crystallization mechanisms, the activation energies were calculated for surface and bulk processes and compared to the differential scanning calorimetry (DSC) results reported earlier. Furthermore, the conversion rate α was calculated from the conductivity data by using the Odolevsky equation, the obtained dependence is in a good agreement with the results from residual enthalpies measurements performed by DSC. In a supplemental study a thorough kinetic analysis was applied to the DSC measurements of residual enthalpies. The observed decrease of the Johnson-Mehl-Avrami kinetic exponent m was explained by decrease in dimensionality of the bulk crystallization process.

Crystallization mechanisms occurring in the Se–Te glassy system

“…As can be seen, the data for batch (b) show commonly observed shifts and curvatures with changing temperature and heating rate, which indicate overlapping ''surface''/bulk crystallization mechanism characteristics for Se-Te glasses. Incidentally, based on our other recent results, it seems that the curvatures [1][2][3][4][5][6][7] observed in the Kissinger plot for Se-Te coarse powders and bulks can be associated with the transition between the formation of two types of spherulitic crystallites (hightemperature type A and low-temperature type B) as identified by Ryschenkow and Faivre and Bisault, Ryschenkow, and Faivre [15,16] for amorphous selenium. Considering the framework of the three types of crystallization mechanism occurring in Se-Te glasses, the two above-mentioned microscopic crystal growth patterns fall within the bulk crystallization mechanism originating from randomly dispersed nuclei.…”

“…Another very interesting fact is associated with the location of the crystallization peaks with respect to the temperature axis compared for different powder fractions. In the case of batch (a) the peaks show almost no shift in temperature with increasing particle size (which is quite unusual considering the so far observed behavior in the Se-Te glassy system [1][2][3][4][5][6][7]), while for batch (b) the crystallization peaks shift to higher temperatures with increasing grain size.…”

“…Experimental details on the preparation and measurements of the Se, Se 90 Te 10 , Se 80 Te 20, and Se 70 Te 30 compositions can be found in the, respective, previously published papers [1][2][3][4][5][6][7]. In addition to these materials, a new glass with Se 95 Te 5 composition was prepared.…”

“…Based on the latter, the interpretations introduced for the formerly studied compositions [1][2][3][4][5][6][7] can be extended for Example DSC curves measured for the twoprepared glass batches (data for similar particle size fraction and heating rate are displayed). Zoomed glass transition region is shown in the inset Crystallization mechanisms occurring in the Se-Te glassy system the current Se 95 Te 5 material.…”

“…Recently, extensive systematic research dealing with macroscopic crystallization in Se-Te glasses was conducted [1][2][3][4][5][6][7]. Two novel methodologies for treating the crystallization data measured by differential scanning calorimetry (DSC) were developed within the framework of these studies.…”