Second-order nonlinear optical (NLO) crystals functioning in the ultraviolet (UV) and deep-ultraviolet (deep-UV) regions are critically important as frequency conversion materials for all-solid-state UV laser devices. In this review, we focus on recent studies of inorganic UV and deep-UV NLO crystals with wide UV transparency and SHG efficiency. Following an introduction describing crystal-design strategies for UV and deep-UV NLO materials, the manuscript is organized according to the type of inorganic anions (borates, carbonates, nitrates and phosphates). Special attention is given to the crystal structures, second-order NLO properties, and structure−property correlations. The concluding remarks highlight future prospects in the field, with emphasis on the superiority of the different types of UV and deep-UV NLO crystals and the importance of large-size crystal growth for practical application in electro-optic devices.

Knowledge of the sound velocity of core materials is essential to explain the observed anomalously low shear wave velocity (VS) and high Poisson’s ratio (σ) in the solid inner core. To date, neither VS nor σ of Fe and Fe-Si alloy have been measured under core conditions. Here, we present VS and σ derived from direct measurements of the compressional wave velocity, bulk sound velocity, and density of Fe and Fe-8.6 wt%Si up to ~230 GPa and ~5400 K. The new data show that neither the effect of temperature nor incorporation of Si would be sufficient to explain the observed low VS and high σ of the inner core. A possible solution would add carbon (C) into the solid inner core that could further decrease VS and increase σ. However, the physical property-based Fe-Si-C core models seemingly conflict with the partitioning behavior of Si and C between liquid and solid Fe.

We theoretically showed that the spontaneous polarization in ferroelectric (FE) nanowires (NWs) can be considerably enhanced due to the nanosize confinement by the first-principles calculations. The spontaneous polarization in a fully-relaxed PbTiO 3 NW with 1.8 nm diameter is 1.26 times higher than that of bulk counterpart. The tension induced by NW surface curvature counteracts the near-surface depolarizing effect and meanwhile leads to the unusual enhancement of spontaneous polarization. These findings indicated that FE NWs can be promising in the applications of nanodevices. a) Correspondingauthor: stsygw@mail.sysu.edu.cn * eff Z is the Born effective charge of the local mode, eff U is the local model of the cell

Two novel noncentrosymmetric metal borates, Ba[BO(OH)] (1) and Na[BO(OH)](HO) (2), have been obtained by hydrothermal and surfactant-thermal means. Compound 1 consists of novel one-dimensional borate chains formed by BO and BO rings, assembled into a three-dimensional (3D) framework by Ba cations. The structure of 2 exhibits double-helical chains constructed from BO primary building units, which are interconnected via Na cations and H-bonding interactions to generate a 3D framework. Second-harmonic-generation (SHG) measurements show that 1 shows a phase-matching powder SHG response of ∼2.2 × KHPO (KDP), while 2 exhibits a weak SHG response. The cutoff edges of 1 and 2 are ∼242 and ∼221 nm, respectively, which suggests that they are potential ultraviolet nonlinear optical (NLO) materials. Band structures and NLO properties have also been theoretically studied.

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Using the dynamic compression technique, the sound velocities of Fe‐11.8 wt % S were measured up to 211.4 (4.5) GPa and 6,150 K. Discontinuities both in shock velocity and sound velocity indicate that Fe‐11.8 wt % S completely melts at a pressure of 111.3 (2.3) GPa. By the energy conservation law, the calculated liquidus temperature is about 2,500 (300) K. Extrapolated to the inner‐core boundary based on the Lindeman law, the liquidus temperature of Fe‐11.8 wt % S is 4,300 (300) K. We developed a thermodynamic model fit to the experimental data, which allows calculation of the densities and sound velocities of liquid Fe‐S under core conditions. For liquid Fe‐11.8 wt % S and Fe‐10 wt % S, good agreement was achieved between the extrapolations using our model and experimental measurements at very low pressure. Under the conditions of the outer core, the densities and bulk sound velocities of Fe‐10 wt % S provide a good fit to observed seismic profiles of Earth's core. Our results imply that an upper limit of 10 wt % S content in Earth's core satisfies the geophysical constraints. Simultaneously considering other geochemical constraints, the outer core may contain about 6 wt % sulfur and 4 wt % silicon.

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