High-temperature compression of ferropericlase and the effect of temperature on iron spin transition

Iron-bearing lower mantle minerals have been proposed to undergo the spin transition at certain P-T conditions. One of the remarkable effects of the spin transition is on the density since this transition is accompanied by a volume shrinkage. The precise density profile of the mantle based on laboratory measurements is important for understanding the composition of the mantle. In order to collect the density data and understand the nature of the spin transition of an iron-bearing lower mantle mineral, we operated high-temperature compression experiments of ferropericlase (Fp) with a composition of (Mg0.81,Fe 0.19)O with in-situ X-ray diffraction method in an externally-heated diamond anvil cell from 19 to 85 GPa at a constant temperature of 859-869 K. Room-temperature experiments with a laser-annealing technique were also carried out on the same material. Anomalous volume reductions that cannot be explained by normal compression behavior were observed at 60-82 GPa and 58-64 GPa at a high temperature and room temperature, respectively. These volume reductions are likely related to the spin transition of ferrous iron in Fp. The observed density changes across this spin transition at 865 and 300 K are about 1.6% and 0.6%, respectively. The spin transition pressure interval expands with increasing temperature. Very recently, in order to obtain further high-temperature data, we operated a new in-situ X-ray diffraction experiment in a laser-heated diamond cell with a membrane system. In this new system, we were able to regulate the gas pressure in the membrane of the DAC and, therefore, compress the sample at a high temperature during the laser-heating. We collected the volume data at high temperature of 1600-1700 K from 20 to 120 GPa. We will discuss the temperature effect of the spin transition in Fp from our external- and laser-heated and room-temperature compression experiments.