arXiv subjects

R. Turnbull

Publications and source records attributed to R. Turnbull.

4 recordsLinked to original sources

arXiv2026

High-Pressure XRD Study of Ti-3Al-2.5V Titanium Alloy: Intermediate Transition Pressure and Composition Trends in Ti-Al-V Alloys

High-pressure X-ray diffraction experiments were performed on Ti-Al-V alloys to investigate the effect of composition on structural stability, focusing on Ti-3Al-2.5V and comparing with pure Titanium and Ti-6Al-4V. Measurements using different pressure-transmitting media show a phase transition in Ti-3Al-2.5V at 17-19 GPa, intermediate between pure Ti (5-10 GPa) and Ti-6Al-4V (~30 GPa). Despite variations arising from the choice of pressure medium, the transition pressure shows a clear and systematic increase with higher Al and V content. Equation-of-state analysis indicates that the bulk modulus remains nearly unchanged across compositions. This suggests a decoupling between elastic properties and phase stability, with alloying primarily affecting the transition pressure rather than compressibility. These results highlight the role of composition in tuning high-pressure phase transformations in Ti-Al-V based alloys.

cond-mat.mtrl-sci↗

arXiv2026

Pressure-induced hypercoordination of iodine and dimerization of I2O6H in strontium di-iodate hydrogen-iodate (Sr(IO3)2HIO3)

In this work, we report evidence of pressure-induced changes in the crystal structure of Sr(IO3)2HIO3 connected to changes the coordination of the iodine atom and the of the configuration of HIO3 and IO3 units. The changes favor iodine hypercoordination and happen in two steps on sample compression. Firstly, at 2.5 GPa, [HIO3]-[IO3] complexes are formed, and secondly, at 4.5 GPa, these complexes form dimers of [HIO3]-[IO3]-[IO3]-[HIO3]. The evidence is obtained from a combined experimental and theoretical study performed up to 20 GPa. Synchrotron powder X-ray diffraction, Raman spectroscopy, and optical-absorption experiments have been complemented with density-functional theory calculations, including the study of the topology of the electron density. The changes observed in the crystal structure are related to the transformation of secondary (halogen) bonds into electron-deficient multicenter bonds. The paper also discusses the effect of pressure on the compressibility of the Sr(IO3)2HIO3 crystal structure, its phonons, the electronic band gap, and the refractive index. Sr(IO3)2HIO3 was found to be highly compressible with an anisotropic compressibility. The softening of the internal I-O vibrations of IO3 units was also observed, together with a decrease of the band-gap energy (from 4.1 eV at 0 GPa to 3.7 eV at 20 GPa), a band-gap crossing, and a change in the topology of the band structure, with Sr(IO3)2HIO3 transforming from a direct gap semiconductor at 0 GPa to an indirect gap semiconductor beyond 6 GPa.

cond-mat.mtrl-sci↗

arXiv2025

High-temperature and high-pressure study on columbite structured ZnNb2O6

High-temperature and high-pressure experiments were conducted on columbite-type ZnNb2O6, reaching temperatures up to 873 K at ambient pressure and pressures up to 30 GPa at ambient temperature, respectively. Through systematic analysis employing synchrotron powder X-ray diffraction and Raman spectroscopy, we examined the crystal structure and phonon behavior. Within the specified temperature range, the orthorhombic phase of ZnNb2O6 (space group: Pbcn) demonstrated notable phase stability, with a thermal expansion coefficient similar to that of isomorphic compounds. Notably, a reversible phase transition was observed under compression at 10 GPa, with diffraction experiments indicating a shift to a monoclinic structure (space group P2/a), which remained stable up to 30 GPa. Changes in Raman modes, lattice parameters, and the unit-cell volume were monitored. A significant 2.5% discontinuity in the unit-cell volume at the phase transition pressure from orthorhombic to monoclinic suggests a first-order phase transition. The bulk moduli of the orthorhombic and monoclinic phases were estimated as 165(7) GPa and 230(9) GPa, respectively- We also found that both phases exhibit an anisotropic response to pressure. Furthermore, first-principles calculations support consistently with experimental observations.

cond-mat.mtrl-sci↗

arXiv2025

Mechanical softening and enhanced elasticity of lunar olivine probed via nanoindentation and high-pressure X-ray diffraction measurements

The mechanical properties of minerals in planetary materials are not only interesting from a fundamental point of view but also critical to the development of future space missions. Here we present nanoindentation experiments to evaluate the hardness and reduced elastic modulus of olivine, (Mg, Fe)2SiO4, in meteorite NWA 12008, a lunar basalt. Our experiments suggest that the olivine grains in this lunaite are softer and more elastic than their terrestrial counterparts. Also, we have performed synchrotron-based high-pressure X-ray diffraction (HP-XRD) measurements to probe the compressibility properties of this meteorite and, for comparison purposes, of three ordinary chondrites. The HP-XRD results suggest that the axial compressibility of the orthorhombic $b$ lattice parameter of olivine relative to terrestrial olivine is higher in NWA 12008 and also in the highly-shocked Chelyabinsk meteorite. The origin of the observed differences is discussed. A simple model combining the results of both our nanoindentation and HP-XRD measurements allows us to describe the contribution of macroscopic and chemical-bond related effects, both of which are necessary to reproduce the observed elastic modulus softening. Such joint analysis of the mechanical and elastic properties of meteorites and returned samples opens up a new avenue for characterizing these highly interesting materials.

astro-ph.EP↗