T273 Advances in Mineral Sciences from Atomistic to Macro Perspectives II: Recognition of Dr. Nancy L. Ross, 2024 Roebling Medalist of the Mineralogical Society of America

Wednesday, 25 September 2024
1:30 PM - 5:30 PM
206B

THERMODYNAMICS OF HIGH PRESSURE RARE EARTH OXIDES AT FORCE AND MOTU

Paper number: T273-14
Program: Technical Sessions
Time: 4:35 PM – 4:50 PM

Authors

Abstract

High pressure research is a major emphasis at Arizona State University. The Facility for Open Research in a Compressed Environment (FORCE) houses a suite of high pressure instruments previously unavailable in the western hemisphere, including a 6000 ton large volume press, a DIA type press capable of pressures up to 70 GPa, an internally heated gas vessel for very large volume experiments up to 0.6 GPa, and a 6 GPa torsional press. FORCE is complemented by the Navrotsky laboratory (Thermotu) which is part of the Center for Materials of the Universe (MotU), and provides unparalleled access to experimental thermochemistry, including high temperature melt solution calorimetry, differential thermal analysis, fast-scanning chip calorimetry, and a 10 MPa high pressure calorimeter. These complementary facilities enable synthesis, characterization, and thermochemical measurements of high pressure materials. We present an overview of FORCE and Thermotu, with recent results from work on rare earth oxides at high pressure, an important class of materials with applications from minerals to ceramics to semiconductors.

Rare earths usually form sesquioxides at ambient conditions, several of which transform from cubic to monoclinic (C to B type) structures at high P and T. Monoxides of rare earths from La to Sm, and Yb, have also been synthesized at similar conditions. We used a combination of computation (DFT), high P-T synthesis in a multi-anvil press, and experimental thermochemistry to predict, synthesize, and characterize B type Er2O3 and Y2O3, and rare earth monoxides YO and NdO. Monoclinic Y2O3 and Er2O3 were synthesized at 4 GPa and 1400 °C and 1100 °C, respectively. Y2O3 exhibits a sluggish decomposition, but the experimental transition enthalpy of –21.63 ± 1.77 kJ/mol, agrees with previous measurements and DFT. For B type Er2O3, the measured transition enthalpy of –11.76 ± 1.47 kJ/mol agrees well with values from DFT. The experimental reaction enthalpy for Y + Y2O3 = 3YO (synthesized at 15 GPa and 1600 °C) is 35.7 kJ/mol ± 5 %, which agrees with the DFT value of 32.7 kJ/mol. For the reaction Nd + Nd2O3 = 3NdO (synthesized at 5 GPa and 1200 °C), the reaction enthalpy was 27.7 ± 8.65 kJ/mol. From these results, P-T slopes were calculated for both YO and NdO. Our results illustrate the range of exciting new science which can exist at the intersection of high pressure and experimental thermodynamics.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404965

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