Stabilization of high-temperature Ag2Se phase at room temperature during the crystallization of an amorphous film

Abstract

Amorphous films of Ag2Se were prepared by laser ablation. After being heated up to 270 °C, the films form oriented crystalline structure of orthorhombic β-modification upon further cooling at temperatures of 110 – 90 °С. The films undergo reversible β↔α phase transitions during the following temperature cycling, while the oriented crystalline structure stays the same. X-ray analysis showed no impurities reflections, excluding the one with very low intensity attributed to an elemental silver. The silver nanocrystals apparently form due to the selenium evaporation from the film surface during heating. The temperature dependence of the film's conductivity coincides with the one for bulk stoichiometric Ag2Se samples.It was shown that a considerable amount of α-Ag2Se is preserved in the film at room temperature even at low cooling rate. This phase is subjected to a significant mechanical stress caused by a density difference between α and β modifications. This circumstance points to the possibility of stabilization of high-temperature superionic modification of Ag2Se at room temperature in a nanolayered structure, in which some alternating layers create a similar stress on the Ag2Se layers.