Pressure-Induced Phase Transitions of Indium Selenide
Rasmussen, Anya Marie
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In2Se3 has potential as a phase-change material for memory applications. Understand- ing its phase diagram is important to achieve controlled switching between phases. Pressure-dependent phase transitions of In2Se3 bulk powders and nanowire samples were studied at room temperature and at elevated temperatures using synchrotron x-ray diffraction and diamond-anvil cells (DACs). α-In2Se3 transforms into the β phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pres- sures in typical semiconductors. The bulk moduli are reported and the c/a ratio for the β phase is shown to have a highly nonlinear dependence on pressure. γ-In2Se3, metastable under ambient conditions, transforms into to the high-pressure β phase between 2.8 GPa and 3.2 GPa in bulk powder samples and at slightly higher pressures, between 3.2 GPa and 3.7 GPa in nanowire samples. While the γ phase bulk modulus is similar to that of the β phase, the decrease due to pressure in the unit cell parameter ratio, c/a, is less than half the decrease seen in the β phase. Using high-temperature DACs, we investigated how elevated temperatures and pressures affect the crystal structure of In2Se3. From these measurements, the high-pressure β phase was found to be metastable. The high-pressure β phase transitions into the high-temperature β phase at temperatures above 380 ◦C.