Piezoelectric Sensing in the Multi-Anvil Press: Expanding the Reach of High-Pressure Rheology Beyond XRD

Measuring deviatoric stress in high-pressure deformation typically relies on X-ray diffraction (XRD), yet limited resolution at low stress can constrain its utility. We developed a complementary, piezoelectric-based method that directly tracks force via single-crystal disks in a cubic or D-DIA multi-anvil press. Although α-quartz sensors exhibited Dauphiné twinning under moderate loads, Ca₃TaGa₃Si₂O₁₄ (CTGS) avoided ferrobielastic switching up to 10 GPa, owing to its much lower elastic compliance (S₁₄), confirmed by Brillouin spectroscopy. Our large-volume-press design uses offset heating, diamond heat sinks, and MgO insulation to maintain stable signals up to 1300 K. Deformation experiments on San Carlos olivine (1–7 GPa, 600–1300 K) compared piezoelectric stress estimates with ring-distortion XRD data. In four runs that reached steady-state creep, we derived a unified exponential flow law consistent with established olivine rheology. Critically, the piezoelectric system resolves stresses below 10 MPa—close to an order of magnitude below XRD’s usual threshold—and can be applied in-house for extended parameter exploration. This synergy of XRD and piezoelectric approaches broadens our ability to probe mantle-relevant stress-strain relations and creep phenomena.