2014/09/23 by Junli Wang, Weiling Fan, Juan Yang +5 · 2 citations
Chemistry · Engineering · Materials Science · #Chalcogenide Semiconductor Thin Films #Chemical engineering #Chemistry #Crystal structure #Crystallography #Differential scanning calorimetry #Materials science #Metastability #Nanocluster Synthesis and Applications #Nanocrystal #Nanotechnology #Oleylamine #Organic chemistry #Orthorhombic crystal system #Phase (matter) #Phase transition #Quantum Dots Synthesis And Properties #Tetragonal crystal system #Thermodynamics
paper · doi:10.1021/cm502317g
openalex publication_date 2014/09/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
First-order solid–solid phase transition of crystalline solids at the nanoscale has attracted an increasing interest in solid-state physics and chemistry, which can be used to alter the properties of materials without changing chemical compositions. Herein, we report the results of our comparative studies on phase transitions between tetragonal ( t ), orthorhombic (β), and cubic (α) polymorphs in Ag 2 Se nanocrystals. A significant discrepancy in stability and phase transition behavior is determined for t -Ag 2 Se nanocrystals, which were prepared separately by two different methods. Differential scanning calorimetry (DSC) and variable-temperature XRD studies reveal that the t -Ag 2 Se nanocrystals prepared by the oleylamine (OLA)-mediated method show a highly temperature- and time-sensitive metastability and undergo a t → β → α → β phase transition during the thermal cycling, in which the t → β transition is exothermic and irreversible, whereas the β → α transition is reversible. Similarly, the reversible β → α structure transition is detected in the β-Ag 2 Se nanocrystals, which were also prepared using the OLA-mediated method with different post-treatment manners and stabilized conditions. In contrast, the t -Ag 2 Se nanocrystals prepared by the PVP-assisted solvothermal method are more stable and exhibit a direct, reversible t → α phase transition without undergoing the β phase; however, when heated to a high temperature, for example, ≥250 °C, the stability of the t phase and the reversibility of the t → α transition will be destroyed due to the sintering and size increase of the sample, which is confirmed by the determination of the t → α → β phase transition in the DSC cycle. The formation of the t phase is attributed to the α → t structure transformation with the temperature cooled from synthetic temperatures (160–220 °C) to room temperature. Moreover, the reasons for the difference in the stabilities and phase transitions of t -Ag 2 Se nanocrystals prepared in our two methods are discussed based on the influences of size, surface (or shape), and defects on the thermodynamics and kinetics of a solid–solid structure transformation.