Polymorphic phase transitions are common in crystalline solids. Recent studies suggest that phase transitions may also exist between two liquid forms with different entropy and structure. Such a liquid-liquid transition has been investigated in various substances including water, Al 2 O 3 -Y 2 O 3 and network glass formers. However, the nature of liquid-liquid transition is debated due to experimental difficulties in avoiding crystallization and/or measuring at high temperatures/pressures. Here we report the thermodynamic and structural evidence of a temperature-induced weak first-order liquid-liquid transition in a bulk metallic glassforming system Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 characterized by non-(or weak) directional bonds. Our experimental results suggest that the local structural changes during the transition induce the drastic viscosity changes without a detectable density anomaly. These changes are correlated with a heat capacity maximum in the liquid. Our findings support the hypothesis that the 'strong' kinetics (low fragility) of a liquid may arise from an underlying lambda transition above its glass transition.

Performance description of the Extreme Conditions Beamline (ECB, P02.2) at PETRA III that is optimized for micro-diffraction at simultaneous high pressure and high and low temperatures created in different diamond anvil cells environments. Additional information of the capabilities of the Extreme Conditions Science Infrastructure for DAC work is provided.

A high-entropy alloy (HEA) of HfNbTiVZr was synthesized using an arc furnace followed by ball milling. The hydrogen absorption mechanism was studied by in situ X-ray diffraction at different temperatures and by in situ and ex situ neutron diffraction experiments. The body centered cubic (BCC) metal phase undergoes a phase transformation to a body centered tetragonal (BCT) hydride phase with hydrogen occupying both tetrahedral and octahedral interstitial sites in the structure. Hydrogen cycling of the alloy at 500 °C is stable. The large lattice strain in the HEA seems favorable for absorption in both octahedral and tetrahedral sites. HEAs therefore have potential as hydrogen storage materials because of favorable absorption in all interstitial sites within the structure.

Glass–ceramic solid electrolytes have been reported to exhibit high ionic conductivities. Their synthesis can be performed by crystallization of mechanically milled Li2S–P2S5 glasses. Herein, the amorphization process of Li2S–P2S5 (75:25) induced by ball milling was analyzed via X-ray diffraction (XRD), Raman spectroscopy, and 31P magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. Several structural building blocks such as [P4S10], [P2S6]4–, [P2S7]4–, and [PS4]3– occur during this amorphization process. In addition, high-temperature XRD was used to study the crystallization process of the mechanically milled Li2S–P2S5 glass. Crystallization of phase-pure β-Li3PS4 was observed at temperatures up to 548 K. The kinetics of crystallization was analyzed by integration of the intensity of the Bragg reflections. 7Li NMR relaxometry and pulsed field-gradient (PFG) NMR were used to investigate the short-range and long-range Li+ dynamics in these amorphous and crystalline materials. From the diffusion coefficients obtained by PFG NMR, similar Li+ conductivities for the glassy and heat-treated samples were calculated. For the glassy sample and the glass–ceramic β-Li3PS4 (calcination at 523 K for 1 h), a Li+ bulk conductivity σLi of 1.6 × 10–4 S/cm (298 K) was obtained, showing that for this system a well-crystalline material is not essential to achieve fast Li-ion dynamics. Impedance measurements reveal a higher overall conductivity for the amorphous sample, suggesting that the influence of grain boundaries is small in this case.

Ba 1−x La x F 2+x covering the whole range of compositions was synthesized by high-energy ball milling of mixtures of BaF 2 and LaF 3 at ambient temperature. The compounds obtained in this way crystallize in the cubic fluorite structure in the range from 0 ≤ x ≲ 0.775 which extends the range for the fluorite-type Ba 1−x La x F 2+x covered up to now (0 ≤ x ≤ 0.55) considerably. By employing 19 F NMR spectroscopy and X-ray (total) scattering, indications for a continuous change from the fluorite (BaF 2) to the tysonite structure (LaF 3) were found. The mechanosynthesized samples showed slightly higher fluoride ion conductivities for the samples with x ≤ 0.40 and clearly smaller conductivities in the case of the samples with x ≥ 0.85 than reported for their monocrystalline counterparts. Two conductivity maxima at x ≈ 0.40 and x ≈ 0.85 and a conductivity minimum at x ≈ 0.75 were observed for the mechanosynthesized Ba 1−x La x F 2+x. For the samples with 0.10 ≤ x ≤ 0.50, exhibiting a dc conductivity in the order of 10 −5 S/cm at 400 K, all fluoride ions seem to be highly mobile at temperatures beyond 453 K. The decrease of the ionic conductivity observed for Ba 1−x La x F 2+x with increasing x in the range from x ≈ 0.50 to x ≈ 0.75 is accompanied by a change of the diffusion behavior and a decrease of the ratio of highly mobile to nonmobile or slow fluoride ions.