ALBA Synchrotron
Researchers have explored the phase diagram of zinc under high pressure and high temperature conditions, finding evidence of a change in its structural behaviour at 10 GPa. Experiments profited from the brightness of synchrotron light at ALBA and Diamond. These results can help to understand the processes and phenomena happening in the Earth’s interior.
Cerdanyola del Vallès, 6th September 2018.
Studying the melting behaviours of terrestrial elements and materials at extreme conditions, researchers can understand the phenomena taking place inside them. This information is of great value for discovering how these materials react in the inner core of Earth but also for other industrial applications. Zinc is one of the most abundant elements in Earth's crust and is used in multiple areas such as construction, ship-building or automobile.
A group of researchers from the University of Valencia, the University of Edinburgh (UK), together with the ALBA Synchrotron and the Diamond Light Source (UK), have analysed the phase diagram of zinc up to 140 GPa and 6000K.
The aim of the study was to check the influence of pressure and temperature on the zinc crystal structure and determine how the density evolves with respect to pressure and temperature. Typically the density of minerals increases by around 50% from the surface of the Earth to the core-mantle boundary due to a huge pressure of around 135 GPa. So, with this experiment, researchers were simulating the same conditions of zinc in the interior of Earth.
During the experiment, they were able to extend the melting curve of zinc of previous studies from 24 GPa to 140 GPa. At 10 GPa, they found a solid-solid phase transition between isomorphic hexagonal structures, corresponding to a second-order isostructural phase transition.
Combining experimental techniques & theoretical calculations
Researchers combined different methodologies in this experiment. High pressure and high temperature X-ray diffraction analysis were performed at I15 beamline (Diamond) and beamline at ALBA. This was possible thanks to a recent setup developed at ALBA and the laser-heated diamond anvil cell measurements (performed at Diamond) for temperatures higher than 1000K. Experimental results were complemented by theoretical calculations using density functional theory (DFT) implemented in the Vienna ab initio simulation package (VASP).
Figure: P-T phase diagram of zinc for P<16 GPa and T<1600K. Square data points correspond to the X-ray diffraction measurements. Solid squares are used for the low pressure hexagonal phase (hcp) and empty symbols for the high pressure hexagonal phase (hcp’). White, red and black circles are melting points from previous studies reported in the literature. The triangles are melting points obtained in the present laser-heating measurements. In the onset of the figure is shown the custom-built vacuum vessel for resistively-heated membrane-type DAC used in the experiments at the ALBA Synchrotron.