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• Sodium germanate glasses permanently densify upon hot compression. • Shear modulus features surprising non-monotonic variation upon increasing pressure. • Only very minor changes in Ge-O coordination are observed. • Shear modulus trend is mostly attributed to decrease in edge-sharing with pressure. • Pressure treatment also induces smaller and more elliptical Ge-O rings. Unlike traditional silicate glasses, germanate glasses often feature non-monotonic variations in material properties (e.g., elastic moduli and glass transition temperature) with varying chemical composition, temperature, and pressure. However, the underlying atomic-scale structural origins remain poorly understood. This is because, in most oxide glasses, the structural changes are quantified through solid-state NMR spectroscopy, but unfortunately the only NMR active germanium isotope (73Ge) has very unfavorable NMR properties. Here, we circumvent this problem by using high-energy X-ray and neutron total scattering coupled with ab initio molecular dynamics simulations as input for Reverse Monte Carlo modeling. In detail, we study the structure and properties of two sodium germanate glasses (10Na 2 O-90GeO 2 and 20Na 2 O-80GeO 2) subjected to permanent densification through hot compression up to 2 GPa at the glass transition temperature. While density as well as Young's and bulk modulus increase with pressure as expected, shear modulus first increases and then decreases slightly at higher pressures. The refined atomistic structure models suggest that the glasses feature a distribution of 4, 5, and 6 coordinated Ge with a majority of 4 and 5 coordinated species. Only minor changes in the Ge–O coordination occur upon hot compression, but a notable transformation of edge- to corner-sharing Ge-polyhedra is found. This anomalous polyhedral packing causes a lower number of angular constraints upon higher pressure treatment, explaining the non-monotonic trend of shear modulus with pressure. We also find that the rings become smaller and less circular upon compression, contributing to the volumetric compaction. These findings may aid the future design of germanate glasses with tailored properties and the general understanding of structure-property relations in oxide glasses. [Display omitted] [ABSTRACT FROM AUTHOR]

• A combined experimental and simulated structural analysis was developed to investigate the correlation between temperature susceptibility and GFA of AY-bearing melts. • The temperature-induced changes in the melt structure mainly stem from the interactions among cations and a lower temperature susceptibility indicates a more stable cationic arrangement. • A balanced network arrangement with less unsteady OAl 3 tri-clusters and a large fraction of steady corner-sharing network units coexisting results in the formation of stable cationic packing. • The scarcity of OAl 3 tri-clusters and strong apex-to-apex connections enable the formation of well-developed IMRO structures (rings/chains) and significantly enhance subsequent vitrification. Despite its significance in both fundamental science and industrial applications, the glass-forming transition in the Al 2 O 3 -Y 2 O 3 (AY) refractory system is not yet fully understood due to the elusive structure evolution upon cooling. Here, atomic-scale structural changes in AY-bearing melts with different compositions and temperatures are tracked by employing in situ high-energy synchrotron X-ray diffraction and empirical potential structure refinement simulation. We find that the glass-forming abilities (GFA) of AY-bearing melts are intriguingly correlated with the dependence of melt structure on temperature. In the case of the Al 2 O 3 and Y 3 Al 5 O 12 (YAG), the observed large structural changes from superheating to undercooling melt (i.e., higher temperature susceptibility) correspond to a low GFA. Conversely, the 74Al 2 O 3 –26Y 2 O 3 (AY26) melt, with the smallest temperature susceptibility, exhibits the highest GFA. Simulation models illustrate that the temperature susceptibility of melt is associated with its atomic arrangement, especially the stability of cation-cation pairs. A balanced network (in AY26 melt), where the unsteady OAl 3 tri-clusters are minimized and steady apex-to-apex connections between adjacent network units are abundant, contributes to stabilizing cationic interactions. This, in turn, fosters the formation of large-sized Al-O-Al rings, which topologically facilitates the subsequent glass-forming transition. Our findings provide new structural insight into the GFA of AY-bearing melts and may expand to other unconventional glass-forming systems to accelerate glassy materials design. [Display omitted] [ABSTRACT FROM AUTHOR]

• Simultaneous tuning of particle size and phase composition of TiO 2-δ nanoparticles was achieved by controllable solidification. • A quantitative model between the particle size and the fraction of rutile phase was established, and the nucleation mechanism of the dual-phase particle was discussed. • TiO 2-δ nanoparticles showed enhanced electrocatalytic activity towards nitrate reduction reaction. Oxygen deficient TiO 2- δ nanoparticle has raised wide research interests as electrocatalysts, however, it is challenging to tune the particle size and phase composition simultaneously to optimize its performance. Here we prepared TiO 2- δ nanoparticles taking advantage of the liquid immiscibility phenomenon in TiO 2 -SiO 2 system by aerodynamic levitation (ALD), and employed a simple parameter, the resident time in the immiscibility region, to achieve simultaneous tuning of particle size and phase composition. A quantitative relationship between the particle size and the mass fraction of rutile phase was established, and the formation mechanism of the two-phase particle was proposed. Furthermore, the synthesized TiO 2- δ nanoparticles were evaluated as electrocatalysts for reducing nitrate to ammonia, which showed better performance than the commercial TiO 2 nanopowder. Results from this work provide a simultaneous tuning strategy for regulating the particle size and phase compositions of TiO 2- δ nanoparticles by controllable solidification, and broaden the potential application of TiO 2- δ. [Display omitted] [ABSTRACT FROM AUTHOR]

La- and Nb-doped BaTi 2 O 5 (BT 2) spherical glasses were prepared by a containerless aerodynamic levitation method and their glass-forming regions were established. It is found that La-doping on the Ba-site (network-modifier) and Nb-doping on the Ti-site (network-former) show distinct difference in the glass-forming region: less than 10 % La can replace Ba whereas 40 % Nb can incorporate into BT 2 glass. The distinction in glass-forming ability induced by La- and Nb-doping is discussed mainly from the structural arrangement of the glass. Raman spectroscopy analysis shows that La-doping elongates the short Ti–O bonds in the distorted [TiO 5 polyhedra and thus relaxes the network. Nb-doping introduces [NbO 6 polyhedra into BT 2 and there exists a critical doping level (20 %), below which incorporation of Nb into BT 2 relaxes the [TiO n polyhedra by shortening the long Ti–O bond and above which [NbO 6 starts to participate in the network skeleton construction resulting in a dramatic change in the glass structure, which is supported by the dramatic change in the exothermic peak on the DTA curves. This work triggers the speculation that the network-modifiers in BT 2 glass possess a very important role in the structure of network-former skeleton than those in glasses based on traditional network-former oxides such as SiO 2 , GeO 2 and B 2 O 3 , which may provide a useful strategy for modifying the properties of these novel glasses by chemical doping. [ABSTRACT FROM AUTHOR]

Thermodynamic/dynamic modeling of liquid immiscibility in silicates is seriously hindered due to lack of in situ investigation on the structural evolution of the melt. In this work, atomic-scale structural evolution of a classic binary silicate immiscible system, SiO 2 –TiO 2 , is tracked by in situ high energy X-ray diffraction (HE-XRD). It is found that both the configuration of [SiO] and the polymerization between them are closely coupled with embedment and extraction of the metallic cations (Ti4+). [SiO] monomer goes through deficit-oxygen and excess-polymerization before liquid‒liquid separation and enables self-healing after liquid‒liquid separation, which challenges the traditional cognition that [SiO 4 monomer is immutable. Ti4+ cations with tetrahedral oxygen-coordination first participate in the network construction before liquid separation. The four-fold Ti–O bond is broken during liquid separation, which may facilitate the movement of Ti4+ across the Si–O network to form TiO 2 -rich nodules. The structural features of nodules were also investigated and they were found highly analogous to that of molten TiO 2 , which implies a parallel crystallization behavior in the two circumstances. Our results shed light on the structural evolution scenario in liquid immiscibility at atomic scale, which will contribute to constructing a complete thermodynamic/dynamic framework describing the silicate liquid immiscibility systems beyond current models. [ABSTRACT FROM AUTHOR]

The aerodynamic levitation provides an efficient technique for the research on thermophysical properties and solidification behavior of refractory materials. However, there is a nonnegligible temperature differences across sample, causing unexpected uncertainty of measurement, such as, thermal expansivity and undercooling limit. We establish thermal filed model with properly simplified boundary condition, and derive quantitative expressions of this ambiguous temperature difference. Here we show that the temperature difference not only related to the average temperature, relative size and thermal conductivity of sample, but significantly influenced by the rotation pattern of sample. A huge temperature differences is almost inevitable when the sample with low thermal conductivity and high melting point is smelted in stationary suspension pattern, however, a drastically reduction of temperature difference can be fulfilled by simply making the sample rotation in up to down pattern. The thermal filed simulation was used to confirm the validity of these theoretical expressions. This work shed light on temperature difference in aerodynamic levitation. Based on this work, one can simply estimate the extent of temperature difference across the sample, and regulated that conveniently if needed, which benefit for novel material preparation and solidification mechanism study based on this technique. [ABSTRACT FROM AUTHOR]

Synchrotron X-ray radiography was used to carry out an in-situ observation of the hydrogen bubble evolution in the liquid Al/solid Ni interconnection. The individual bubble mainly grows in a stochastic way during heating. The size distribution for groups of bubbles follows a Gaussian distribution in the early stage and Lifshitz-Slyozov-Wagner (LSW) diffusion controlled distribution in the final stage. The intermetallic compounds (IMCs) first form during solidification, following by the hydrogen bubbles. The bubbles between two adjacent Al 3 Ni grains grow unidirectionally along the liquid channel, with the bottom being impeded by the Al 3 Ni phase and the radius of the growth front being smaller. For the bubbles at triple junctions, they grow along the liquid channel and the crack with morphology transition. [ABSTRACT FROM AUTHOR]