The discovery of superconductivity at 203 K in H3S 1 brought attention back to conventional superconductors whose properties can be described by the Bardeen-Cooper-Schrieffer (BCS) and the Migdal-Eliashberg theories. These theories predict that high, and even room temperature superconductivity (RTSC) is possible in metals possessing certain favorable parameters such as lattice vibrations at high frequencies. However, these general theories do not suffice to predict real superconductors. New superconducting materials can be predicted now with the aid of first principles calculations based on Density Functional Theory (DFT). In particular, the calculations suggested a new family of hydrides possessing a clathrate structure, where the host atom (Ca, Y, La) is at the center of the cage formed by hydrogen atoms 2-4 . For LaH10 and YH10 superconductivity, with critical temperatures Tc ranging between 240 and 320 K is predicted at megabar pressures 3-6 . Here, we report superconductivity with a record Tc  250 K within the Fm3m structure of LaH10 at a pressure P  170 GPa. We proved the existence of superconductivity at 250 K through the observation of zero-resistance, isotope effect, and the decrease of Tc under an external magnetic field, which suggests an upper critical magnetic field of 120 T at zerotemperature. The pressure dependence of the transition temperatures Tc (P) has a maximum of 250-252 K at the pressure of about 170 GPa. This leap, by  50 K, from the previous Tc record of 203 K 1 indicates the real possibility of achieving RTSC (that is at 273 K) in the near future at high pressures and the perspective of conventional superconductivity at ambient pressure.

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, has yet to be experimentally confirmed.Here we show that at pressures of ~200 GPa (∼5.0 fold compression), Na becomes

At ambient pressure, sodium, chlorine, and their only known compound NaCl, have well-understood crystal structures and chemical bonding. Sodium is a nearly-freeelectron metal with the bcc structure. Chlorine is a molecular crystal, consisting of Cl 2 molecules. Sodium chloride, due to the large electronegativity difference between Na and Cl atoms, has highly ionic chemical bonding, with stoichiometry 1:1 dictated by charge balance, and rocksalt (B1-type) crystal structure in accordance with Pauling's rules. Up to now, Na-Cl was thought to be an ultimately simple textbook system. Here, we show that under pressure the stability of compounds in the Na-Cl system changes and new materials with different stoichiometries emerge at pressure as low as 25 GPa. In addition to NaCl, our theoretical calculations predict the stability of Na 3 Cl, Na 2 Cl, Na 3 Cl 2 , NaCl 3 and NaCl 7 compounds with unusual bonding and electronic properties. The bandgap is closed for the majority of these materials. Guided by these predictions, we have synthesized cubic NaCl 3 at 55-60 GPa in the laser-heated diamond anvil cell at temperatures above 2000 K.

Material design in terms of their morphologies other than solid nanoparticles can lead to more advanced properties. At the example of iron oxide, we explored the electrochemical properties of hollow nanoparticles with an application as a cathode and anode. Such nanoparticles contain very high concentration of cation vacancies that can be efficiently utilized for reversible Li ion intercalation without structural change. Cycling in high voltage range results in high capacity (∼132 mAh/g at 2.5 V), 99.7% Coulombic efficiency, superior rate performance (133 mAh/g at 3000 mA/g) and excellent stability (no fading at fast rate during more than 500 cycles). Cation vacancies in hollow iron oxide nanoparticles are also found to be responsible for the enhanced capacity in the conversion reactions. We monitored in situ structural transformation of hollow iron oxide nanoparticles by synchrotron X-ray absorption and diffraction techniques that provided us clear understanding of the lithium intercalation processes during electrochemical cycling.