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The observation of high- T c superconductivity (HTSC) in concomitant with pressure-induced orthorhombic-tetragonal structural transition in bilayer La 3 Ni 2 O 7 has sparked hopes of achieving HTSC by stabilizing the tetragonal phase at ambient pressure. Chemical pressure, introduced by replacing La 3+ with smaller rare-earth R 3+ has been considered as a potential route. However, our experimental and theoretical investigation reveals that such substitutions, despite causing lattice contraction, actually produce stronger orthorhombic distortions, requiring higher pressures for the structural transition. A linear extrapolation of P c versus the average size of A -site cations (< r A >), yields a putative critical value of < r A > c ≈ 1.23 Å for P c ≈ 1 bar. The negative correlation between P c and < r A > indicates that replacing La 3+ with smaller R 3+ ions is unlikely to reduce P c to ambient pressure. Instead, substituting La 3+ with larger cations like Sr 2+ or Ba 2+ might be a feasible approach. Our results provide guidance for realizing ambient-pressure HTSC in bilayer nickelates.

The low-melting glass of Bi 2 O 3 -B 2 O 3 -SiO 2 (BiBSi) system was used for the first time for laser sealing of vacuum glazing. Under the condition of constant boron content, how the structure and properties vary with Bi/Si ratio in low-melting glass was investigated. In addition, the relationships between laser power, low-melting glass solder with different Bi/Si ratios and laser sealing shear strength were revealed. The results show that a decrease in the Bi/Si ratio can cause a contraction of the glass network of the low-melting glass, leading to an increase of its characteristic temperature and a decrease of its coefficient of thermal expansion. During laser sealing, the copper ions in the low-melting glass play an endothermic role. A change in the Bi/Si ratio will affect the valence state transition of the copper ions in the low-melting glass. The absorbance of the low-melting glass does not follow the expected correlation with the Bi/Si ratio, but shows a linear correlation with the content of divalent copper ions. The greater the concentration of divalent copper ions, the greater the absorbance of the low-melting glass, and the lower the laser power required for laser sealing. The shear strength of the low melting glass solder after laser sealing was tested, and it was found that the maximum shear strength of Z1 glass sample was the highest up to 2.67 MPa.

A series of bioactive glass scaffolds doped with SrO or ZnO (0, 5, and 10 mol%) were synthesized by the foam replica and melting method. The thermodynamic evolution, phase composition, microstructure, ion release, in vitro bioactivity, and oxygen density of the scaffolds were characterized. The proliferation of murine long bone osteocyte Y4 cells was studied by cell culture. The survival rate of the BGs evaluated the antibacterial activity and Escherichia coli strains in co-culture. The results indicated that the process window decreases with the increase of dopants. All the samples have a pore structure size of 200–400 μm. When the scaffolds were immersed in simulated body fluid for 28 days, hydroxyapatite formation was not affected, but the degradation process was retarded. The glass network packing and ionic radii variations of the substitution ions control surface degradation, glass dissolution, and ion release. MTT results revealed that 5Sr-BG had a significant effect on promoting cell proliferation and none of the BGs were cytotoxicity. Sr-BGs and Zn-BGs exhibited significantly inhibited growth against E. coli bacterial strains. Generally, these results showed the 5Sr-BG scaffold with high vitro bioactivity, cell proliferation, and antibacterial property is an important candidate material for bone tissue regeneration and repair.

The Ruddlesden–Popper (R–P) bilayer nickelate, La 3 Ni 2 O 7 , was recently found to show signatures of high-temperature superconductivity (HTSC) at pressures above 14 GPa (ref.  1 ). Subsequent investigations achieved zero resistance in single-crystalline and polycrystalline samples under hydrostatic pressure conditions 2 – 4 . Yet, obvious diamagnetic signals, the other hallmark of superconductors, are still lacking owing to the filamentary nature with low superconducting volume fraction 2 , 4 , 5 . The presence of a new 1313 polymorph and competing R–P phases obscured proper identification of the phase for HTSC 6 – 9 . Thus, achieving bulk HTSC and identifying the phase at play are the most prominent tasks. Here we address these issues in the praseodymium (Pr)-doped La 2 PrNi 2 O 7 polycrystalline samples. We find that substitutions of Pr for La effectively inhibit the intergrowth of different R–P phases, resulting in a nearly pure bilayer structure. For La 2 PrNi 2 O 7 , pressure-induced orthorhombic to tetragonal structural transition takes place at P c  ≈ 11 GPa, above which HTSC emerges gradually on further compression. The superconducting transition temperatures at 18–20 GPa reach T c onset = 82.5 K and T c zero = 60 K , which are the highest values, to our knowledge, among known nickelate superconductors. Importantly, bulk HTSC was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa. Our results not only resolve the existing controversies but also provide directions for exploring bulk HTSC in the bilayer nickelates. Bulk high-temperature superconductivity observed in pressurized tetragonal La 2 PrNi 2 O 7 was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa.

The recent report of near-ambient superconductivity in the nitrogen-doped lutetium hydride has attracted considerable attention. Subsequent follow-up studies confirmed the pressure-induced color changes in both N-free and N-doped LuH 2 but failed to reproduce superconductivity. It remains a puzzle why the samples in the original report exhibited pronounced resistance anomaly reminiscent of the superconducting transition. Here, we show that percolation of metallic grains with high conductivity through the insulating surfaces in cold-pressed LuH 2 samples can occasionally produce sharp resistance drops, which even display magnetic field and/or current dependences but stay far from zero resistance. The insulating surface of LuH 2 grain should be attributed to the modification of hydrogen stoichiometry or the contamination by oxygen/nitrogen, resulting in an increase of resistance by over six orders of magnitude. Such an effect is more significant than that discovered recently in LaH 3± x , which may indicate that LuH 2 can be a potential superionic conductor. Our results call for caution in asserting the resistivity drops as superconductivity and invalidate the background subtraction in analyzing the corresponding resistance data.

The recent report of near-ambient superconductivity in the nitrogen-doped lutetium hydride has attracted considerable attention. Subsequent follow-up studies confirmed the pressure-induced color changes in both N-free and N-doped Lu[H.sub.2] but failed to reproduce superconductivity. It remains a puzzle why the samples in the original report exhibited pronounced resistance anomaly reminiscent of the superconducting transition. Here, we show that percolation of metallic grains with high conductivity through the insulating surfaces in cold-pressed Lu[H.sub.2] samples can occasionally produce sharp resistance drops, which even display magnetic field and/or current dependences but stay far from zero resistance. The insulating surface of Lu[H.sub.2] grain should be attributed to the modification of hydrogen stoichiometry or the contamination by oxygen/nitrogen, resulting in an increase of resistance by over six orders of magnitude. Such an effect is more significant than that discovered recently in La[H.sub.3][+ or -]x, which may indicate that Lu[H.sub.2] can be a potential superionic conductor. Our results call for caution in asserting the resistivity drops as superconductivity and invalidate the background subtraction in analyzing the corresponding resistance data. Lu[H.sub.2], percolation, resistance drop, superconductivity, superionic conductor PACS number(s): 64.60.Ak, 74.10.+v, 61.10.Nz, 66.30.Hs

The Ruddlesden-Popper (R-P) bilayer nickelate, La Ni O , was recently found to show signatures of high-temperature superconductivity (HTSC) at pressures above 14 GPa (ref.  ). Subsequent investigations achieved zero resistance in single-crystalline and polycrystalline samples under hydrostatic pressure conditions . Yet, obvious diamagnetic signals, the other hallmark of superconductors, are still lacking owing to the filamentary nature with low superconducting volume fraction . The presence of a new 1313 polymorph and competing R-P phases obscured proper identification of the phase for HTSC . Thus, achieving bulk HTSC and identifying the phase at play are the most prominent tasks. Here we address these issues in the praseodymium (Pr)-doped La PrNi O polycrystalline samples. We find that substitutions of Pr for La effectively inhibit the intergrowth of different R-P phases, resulting in a nearly pure bilayer structure. For La PrNi O , pressure-induced orthorhombic to tetragonal structural transition takes place at P  ≈ 11 GPa, above which HTSC emerges gradually on further compression. The superconducting transition temperatures at 18-20 GPa reach and , which are the highest values, to our knowledge, among known nickelate superconductors. Importantly, bulk HTSC was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa. Our results not only resolve the existing controversies but also provide directions for exploring bulk HTSC in the bilayer nickelates.

The structure and properties of lithium aluminosilicate glasses containing Y^sub 2^O^sub 3^ were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and Raman spectroscopy. Effects of yttria on the viscosity of LAS glasses were investigated, and found that the introduction of yttria effectively decreased the viscosity of LAS glasses. In Raman spectra of initial glasses it is shown the starting glasses are in almost complete disorder, since all bands are weak and broad. In the spectra of heat-treated specimens some new narrow bands appear and increase in intensity, and the frequency changes with varied yttria addition. The DTA and XRD results show that yttria controlled the crystallization of LAS glasses by increasing the crystallization peak temperature (T ^sub p^), however, the main crystalline phase of glass-ceramics was β-spodumene.[PUBLICATION ABSTRACT]

We synthesized polycrystalline La3Ni2O7 samples by using the sol-gel method without post-annealing under high oxygen pressure, and then measured temperature-dependent resistivity under various hydrostatic pressures up to 14.5 GPa in a cubic anvil cell apparatus. We find that the density-wave-like anomaly in resistivity is progressively suppressed with increasing pressure and the resistivity drop corresponding to the onset of superconductivity emerges at pressure as low as 7 GPa. Zero resistivity is achieved at 9 GPa below 6.6 K, which increases quickly with pressure to 35.6 K at 14.5 GPa. The observation of zero-resistance state in the polycrystalline La3Ni2O7 samples under high pressures not only corroborates the recent report of superconductivity in the pressurized La3Ni2O7 crystals but also facilitates further studies on this emerging family of nickelate high-Tc superconductors.

We report on the pressure dependence of superconducting transition temperature Tc and upper critical field Bc2(0) through electrical transport of the Ti4Co2O superconductor (eg.,the superconducting transition temperature Tc = 2.5 K and the Bc2(0)=7.2T=2.9Tc). We find that the Tc exhibits non-monotonic pressure dependence:it rises monotonically at first with a pressure coefficient of dTc/dP=0.034 K/GPa, but rapidly decreases around 10-20 GPa, and then increases with the dTc/dP = 0.023 K/GPa, up to= 4.31 K at 69.7 GPa. Concurrently, the Bc2(0)exhibits a dome shaped pressure dependence, with its maximum at 5 GPa of almost twice the value at ambient pressure, exceeding the weak-coupling Pauli paramagnetic limit Bp throughout the whole pressure range. By comparing the normal-state and superconducting properties, we identify two distinct superconducting regimes, with a low-pressure superconducting phase characterized by an enhanced Bc2(0)values and Fermi-liquid normal-state electrical transport (the exponent n = 2), and a high-pressure superconducting phase with a monotonically increased Tc and an enhancement in phonon scatterings (the exponent n = 4). Room-temperature synchrotron X-ray diffraction indicates that there is no structural transition up to 55.8 GPa, which gives a relatively large bulk modulus of 192 GPa in comparison with other alloy superconductors. First-principles calculations suggest that the nonmonotonic Tc maybe closely related to the evolution of the density of states of Ti4Co2O upon compression, which is different from those of isostructural superconductors Ti4Ir2O and Nb4Rh2C. Our results show that even in the Ti4Co2O with weak spin-orbit coupling, superconductivity remains highly sensitive to the external stimuli such as pressure.