Jesse S. Smith

We describe the use of a multi-axis diamond anvil cell (MDAC) as a triaxial deformation apparatus for high-pressure studies with in situ synchrotron x-ray diagnostics. The MDAC employs six independently driven diamond anvils in a cubic geometry, enabling near-uniform compression to high pressures followed by controlled differential loading along orthogonal axes. This architecture largely decouples pressure generation from deviatoric stress application—a persistent limitation of conventional diamond anvil cells (DACs)—and provides independent control of the stress path. We present the experimental methodology, including lattice-strain analysis adapted for the MDAC geometry, sample-strain measurement using combined encoder readings and x-ray radiography, texture analysis, and detector calibration for modular area detectors. The capabilities of the device are demonstrated through deformation experiments on polycrystalline MgO at ∼12 GPa. The MDAC preserves a nearly texture-free sample state during initial near-uniform compression and resolves the onset of lattice preferred orientation development, lattice-strain reflection ordering and its reversal upon yielding, and subsequent plastic evolution. Comparison with results from deformation-DIA and conventional DAC experiments in the literature indicates that the MDAC can access deformation states that are difficult to isolate in existing devices. The instrument is applicable to a broad range of materials that require controlled multi-axis stress states at high pressure and simultaneous structural and textural characterization.

Instead of infinite tellurium chains, LaCu _x Te ₂ intrinsically forms a statistically disordered collinear arrangement of monotelluride and oligotelluride species, yielding semiconducting transport and quasi-linear magnetoresistance at low temperatures.

Anomalous lattice expansion of bcc Ta is observed in helium-loaded diamond anvil cell (DAC) experiments near 6 GPa and above 400 K, while co-loaded W, Mo, and Au exhibit normal thermal expansion. The Ta volume expansion increases with temperature, reaching ∼13% near 650 K before plateauing, and is largely retained after recovery to ambient conditions. Time-resolved measurements at 500 K reveal progressive expansion over several hours, consistent with gradual, thermally activated He incorporation. The largely retained expansion during subsequent cooling and holding at 400 K indicates that the incorporated He is predominantly kinetically trapped. The data reveal two distinct regimes: below ∼550 K, modest and spatially uniform expansion consistent with interstitial He trapping at isolated, randomly distributed vacancies; above ∼550 K, He-vacancy cluster growth producing dramatically larger expansion, peak broadening, and a core–shell microstructure revealed by micrometer-resolution x-ray diffraction mapping. These results demonstrate that He is not always a passive pressure medium in DAC experiments and reveal a previously unrecognized regime of He-mediated lattice modification in Ta, complementing conventional ion-implantation studies relevant to nuclear and fusion structural materials.

The volume compression of body-centered cubic tantalum has been measured to 433 GPa in the standard bevel and toroidal diamond anvil cell (DAC) using synchrotron-based angle-dispersive powder x-ray diffraction. Six experiments were carried out achieving a maximum pressure of 433(6) GPa. Pressures were estimated using an equation of state (EoS) of Cu or Bi for all experiments. We additionally calculated the elastic constants of Ta and Bi and used our previously calculated values for Cu to inform the stress state of the sample and an EoS of Ta for comparison to our experimental data. Our experimental pressure–volume data for Ta was fit with a fourth-order Vinet EoS, resulting in parameters K0 = 192(5) GPa, η = 6.4(6), β = −35(5), and Ψ = 141(13). This Ta EoS is consistent within uncertainty with the ultrasonically derived ambient isothermal bulk modulus, with existing DAC data up to 100 GPa, and with Ta ramp EoS measurements that exceed the pressures of the current study.

The high pressure equation of state for the W 0.75 R e 0.25 alloy is experimentally determined up to 183 GPa with synchrotron angle-dispersive powder x-ray diffraction in the diamond-anvil cell and to ∼925 GPa with density-functional theory. W-Re alloys are used in many industrial high-temperature applications and as a confining gasket material in high-pressure diamond-anvil cell research. The inclusion of 25 wt. % Re achieves the highest performance in terms of strength and ductility while also maintaining the body-centered-cubic (bcc) crystal structure, yet to date there has been no investigation into its elastic behavior at high pressure. We present the experimentally and theoretically determined volumetric and elastic pressure response and systematically compare these results to other W-Re alloys, finding that the bulk modulus of W-Re alloys varies nonlinearly with Re content and W 0.75 Re 0.25 becomes less incompressible than W at 85 GPa.

High-pressure β-Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression. However, the mechanism and transition kinetics remain poorly understood. Here, we investigate the formation of metastable phases and nanostructures in germanium via controllable transition pathways of β-Sn Ge under rapid decompression at different rates. High-resolution transmission electron microscopy reveals three distinct metastable phases with the distinctive nanostructures: an almost perfect st12 Ge crystal, nanosized bc8/r8 structures with amorphous boundaries, and amorphous Ge with nanosized clusters (0.8–2.5 nm). Fast in situ x-ray diffraction and x-ray absorption measurements indicate that these nanostructured products form in certain pressure regions via distinct kinetic pathways and are strongly correlated with nucleation rates and electronic transitions mediated by compression rate, temperature, and stress. This work provides deep insight into the controllable synthesis of metastable materials with unique crystal symmetries and nanostructures for potential applications.