Gold is a compelling element. It is among the least reactive and its crystalline structure is thought to be stable at extremely high pressure. However, the material is considered the "gold standard" for calculating pressure in experiments with static diamond anvils.
At a time when it is gradually compressing at room temperature (on demand for seconds to minutes), gold prefers to be a face-oriented cubic (FCC) structure with weights up to three times the center of the Earth.
Recently, scientists at the Lawrence Livermore National Laboratory (LLNL) and the Carnegie Institution of Washington found that as gold compresses rapidly in nanoseconds (1 billionth of a second), increasing pressure and temperature changes the crystal structure to a new phase of gold. This exceptional body-oriented cubic (bcc) structure is transformed into a more open crystalline structure than the fcc structure.
Lead author Richard Briggs, a doctoral researcher at LLNL, said: "We have discovered a new structure in gold that exists in extreme states – two-thirds of the pressure found in the center of the Earth. The new structure actually has less efficient packaging at higher pressure than the original structure, which was surprising given the huge amount of theoretical predictions that point to the more tightly packed structures that must exist. "
The scientists conducted experiments in the Dynamic Compression Sector (DCS) at the Advanced Photon Source, Argon National Laboratory. DCS is the first synchrotron X-ray device dedicated to the science of dynamic pressure. These consumer experiments were one of the first conducted on the hutch-C, DCS's dedicated high-energy laser station. Gold was the ideal object of thought because of its high Z and generally unexplored phase diagram at high temperatures.
Scientists have discovered that the structure of gold began to change at a pressure of 220 GPa (2.2 million times the earth's atmospheric pressure) and began to melt when compressing above 250 GPa.
Briggs said: "The observation of liquid gold at 330 GPa is amazing. This is the pressure in the center of the Earth and is over 300 GPa higher than previous high pressure liquid gold measurements. "
This conversion of fcc to bcc structure is perhaps one of the most considered phase transitions because of its importance in the assembly of steel, where high temperatures or stresses cause a change in structure between the two fcc / bcc structures.
However, it is not aware of which phase transition mechanism is responsible. The results of the study group indicate that gold underwent a similar phase change before melting as a result of both pressure and temperature, and future tests focused on the transition tool may help explain key details about this a significant change in the assembly of healthy steels.
Briggs says: "Many of the theoretical models of gold used to understand high-pressure / high-temperature behavior do not predict the formation of a body-oriented structure – only two of more than 10 published works. Our results can help theorists refine their models of elements in extreme compression and look at the use of these new models to investigate the effects of chemical bonding to help develop new materials that can be formed in extreme states . "
The study was published in the journal Physical Review Letters.