Detection of thin film phase transformations at high-pressure and high-temperature in a diamond anvil cell

Quantifying how grain size and/or deviatoric stress impact (Mg,Fe)2SiO4 phase stability is critical for advancing our understanding of subduction processes and deep-focus earthquakes. Here, we demonstrate that well-resolved X-ray diffraction patterns can be obtained on nano-grained thin films within laser-heated diamond anvil cells (DACs) at hydrostatic pressures up to 24 GPa and temperatures up to 2300 K. Combined with well-established literature processes for tuning thin film grain size, biaxial stress, and substrate identity, these results suggest that DAC-loaded thin films can be useful for determining how grain size, deviatoric stress, and/or the coexistence of other phases influence high-pressure phase stability. As such, this novel DAC-loaded thin film approach may find use in a variety of earth science, planetary science, solid-state physics, and materials science applications. High pressure laboratory experiments on thin film Mg2SiO4 show that the wadsleyite-ringwoodite phase transition occurs at approximately 500 K higher temperature than expected from bulk mineral data and may be more realistic for fine-grained, high-strain shear zones.