High pressure phase transformation studies on Rare Earth Sesquioxides

Abstract

The structural changes that occur in rare earth sesquioxides under high pressure have been investigated. The work consists of mainly high pressure X-ray diffraction, micro Raman and electrical resistivity studies using designer diamond anvils on rare earth sesquioxides. High-pressure X-ray diffraction studies on gadolinium sesquioxide (Gd2O3) have been carried out up to a pressure of ~25 GPa in a diamond-anvil cell at room temperature. Gadolinium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase at around 12 GPa. The high-pressure phase has been identified as the hexagonal La2O3-type structure. The bulk modulus and the pressure derivative of this phase have been obtained. High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho2O3) have been carried out up to a pressure of ~17 GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5 GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The bulk modulus of the parent phase is reported. In situ electrical resistivity studies using designer diamond anvils have been carried out and this study reveals an increase in the resistivity around 16 GPa which corresponds to the phase transition seen in high-pressure X-ray diffraction and Raman studies. The stability regions for some of the rare earth sesquioxides under high pressure and ambient temperatures have been determined and also an attempt has been made to understand the nature of these transitions in each case. A commercial electric discharge machine meant for removing taps was modified to drill holes of size ~100 to 250and#956;m in Stainless Steel gaskets for carrying out High Pressure experiments using DACs. Also an innovative jig for mounting the diamond anvils were designed, fabricated and utilized for the present investigations.