Anomalous Behavior in the Electrical and Optical Properties of Ammonium Sulfate Single Crystals in the Temperature Range 250–350 K

概要

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Optical and electrical properties of Ammonium sulfate crystals (AS) were investigated in the temperature range 250–350 K. Optical constants of AS crystal were calculated at room temperature. The optical absorption coefficient $\alpha$ was analyzed and interpreted to be due to the allowed direct transition, hence the values of the allowed direct energy gap $E_{\text{g}}$ were calculated. The parameter $\sigma$ characterizing the broadening of the absorption edge was investigated as a function of temperature. Both $E_{\text{g}}$ and $\sigma$ showed anomalies at 286 and 303 K. Domain structure observations in the temperature range 250–350 K revealed the starting of a ferroelastic phase of AS at 286 K. This structure contains sometimes three kinds of domains and sometimes with two kinds of domains for the temperatures from 286 up to 303 K. At temperatures higher than 303 K, a stable phase with three kinds of domains was observed. Anomalies in the electrical conductivity behavior were detected at 286 and 303 K. This implies the occurrences of possible phase transitions at these two different temperatures.
Physical Society of Japanの論文
2002-10-15