Anomalous high pressure behaviour in nanosized rare earth sesquioxides

Abstract

We report Raman spectroscopic studies of the nanosized rare earth sesquioxides, namely yttrium sesquioxide (Y(2)O(3)), gadolinium sesquioxide (Gd(2)O(3)) and samarium sesquioxide (Sm(2)O(3)), under high pressure. The samples were characterized using x-ray diffraction, Raman spectroscopy and atomic force microscopy at atmospheric pressures. Y(2)O(3) and Gd(2)O(3) were found to be cubic at ambient, while Sm(2)O(3) was found to be predominantly cubic with a small fraction of monoclinic phase. The strongest Raman peaks are observed at 379, 344 and 363 cm(-1), respectively, for Y(2)O(3), Sm(2)O(3) and Gd(2)O(3). All the samples were found to be nanosized with 50-90 nm particle sizes. The high pressures were generated using a Mao-Bell type diamond anvil cell and a conventional laser Raman spectrometer is used to monitor the pressure-induced changes. Y(2)O(3) seems to undergo a crystalline to partial amorphous transition when pressurized up to about 19 GPa, with traces of hexagonal phase. However, on release of pressure, the hexagonal phase develops into the dominant phase. Gd(2)O(3) is also seen to develop into a mixture of amorphous and hexagonal phases on pressurizing. However, on release of pressure Gd(2)O(3) does not show any change and the transformation is found to be irreversible. On the other hand, Sm(2)O(3) shows a weakening of cubic phase peaks while monoclinic phase peaks gain intensity up to about a pressure of 6.79 GPa. However, thereafter the monoclinic phase peaks also reduce in intensity and mostly disordering sets in which does not show significant reversal as the pressure is released. The results obtained are discussed in detail.

Raman scattering of rare earth sesquioxide Ho2O3: A pressure and temperature dependent study

“…In the present study, it is interesting to note that contrary to the cubic to hexagonal phase transitions observed in our previous reports of Dy 2 24,26 It is noteworthy that there exist several ways of transformation between the various phases, depending on temperature and pressure conditions. 27,28 Additional reaction components can also help to transform the sesquioxides during the temperature treatment.…”

“…30 In the previous similar observations in the case of Eu 2 O 3 and Sm 2 O 3 , the starting material was found to contain traces of non-stoichiometric phase and monoclinic phase, respectively. 24,26 In the present case also at ambient and at a low pressure of 1.32 GPa, a broad hump is seen around 600-700 cm…”

Pressure‐induced anomalous phase transformation in nano‐crystalline dysprosium sesquioxide

“…[8,11 -13] Recently, the authors have reported cubic to hexagonal transformation in nano-crystalline Gd 2 O 3 and Y 2 O 3 . [14] This transformation had been reported for 439 Phase transformation in nano-crystalline Dy 2 O 3 under high pressures the first time in case of Y 2 O 3 . There have also been a few recent reports of cubic to hexagonal transformation in Gd 2 O 3.…”

“…[14] Zhang et al [15] also obtained an irreversible C → A transition in Gd 2 O 3 between 7 and 15 GPa which returned to monoclinic phase on release. At normal pressures the hexagonal phase is only known to be stable at high temperatures.…”

“…[11,14] It has been reported that for A-type Ln 2 O 3 , four vibrational Raman modes are active in Raman scattering and correspond to two stretching vibrations, i.e. A 1g and E g , and two bending vibrations of the A 1g and E g .…”