It is of great difficulty to obtain deep-UV transparent materials with enhanced second harmonic generation (SHG), mainly limited by the theoretically poor transparency of these materials in the deep-UV spectral region. Here we report a new noncentrosymmetric, deep-UV transparent phosphate RbNaMgPO, which undergoes a thermo-induced reversible phase transition (at a high temperature of 723 K) and correspondingly an evident SHG enhancement up to ∼1.5 times. The phase transition is aroused by the twist of [PO] dimers with deviation from the P-O-P equilibrium positions. Theoretical analyses reveal that the enhanced SHG can be ascribed to the thermo-induced collective alignment of SHG-active [PO] dimers along the polar axis of high-temperature phase. This work provides an unprecedented physical routine (to SHG-enhanced materials) that is distinguished from the traditional one by chemical design and synthesis.

Intrinsic isotropic near-zero thermal expansion is discovered in borate crystal Zn B O with high transparency in the ultraviolet region. First-principles calculations demonstrate that the very low thermal expansion originates mainly from the invariability of the solid [B O ] truncated octahedra that are fixed by the [Zn O ] clusters in the ZBO structure.

Cubic perovskite SrCoO3−δ was successfully prepared through simple anion F-doping and demonstrated great OER performance.

Lead-free zero-dimensional (0D) organic−inorganic metal halide hybrids have recently attracted special attention as luminescent materials. However, their structural stability is still a challenge for the further development. Here, we select Sn 4+ as the B-site inorganic cation and obtain a new tin(IV)-based organic−inorganic metal halide hybrids (C 6 N 2 H 16 Cl) 2 SnCl 6 with remarkable air stability. (C 6 N 2 H 16 Cl) 2 SnCl 6 exhibits a blue broadband emission originating from self-trapping excitons (STEs) and the emission intensity remains stable for over three months. When the temperature rises to 450 K, the intensity of photoluminescence can maintain about 50%, indicating the good thermal stability of (C 6 N 2 H 16 Cl) 2 SnCl 6 . This work presents a new strategy toward the tin(IV)-based photoluminescent organic−inorganic metal halide hybrids with environmentally friendly, high stability characteristics.

Developing superior deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials is a great challenge because of the contradiction between deep-UV transparency and enhanced second harmonic generation (SHG), especially for deep-UV NLO phosphates in which the constituent P−O groups have relatively small microscopic SHG coefficients. Here we report a new noncentrosymmetric phosphate Cs 2 LiPO 4 (I), whose crystal structure consists of [LiPO 4 ] ∞ layered structural units with a novel honeycomb-like topology. As compared with the benchmark deep-UV NLO material KBe 2 BO 3 F 2 , I is beryllium-free, and it is relatively easy to grow its large single crystals because of its congruent melting. Furthermore, it not only is deep-UV transparent but also exhibits an unexpectedly enhanced SHG response of 1.8 × KH 2 PO 4 that hits a new high in deep-UV NLO phosphates. These results demonstrate that I satisfies the key requirements of being a promising deep-UV NLO candidate. Theory calculations and structural analysis reveal that the enhanced SHG response can be attributed to the honeycomb-like topological structure, which endows the constituent [PO 4 ] 3− monomers of I with an aligned arrangement and as a result a favorable superposition of their microscopic SHG coefficients. These findings may provide useful insights into the development of both deep-UV NLO materials and honeycomb-like topological structures.

High-performance infrared (IR) nonlinear optical (NLO) materials with large NLO response and suitable birefringence are urgently needed for various applications. A Hg-based IR NLO material KHg4Ga5Se12 with such desirable properties has been newly discovered. In the structure, obviously distorted HgSe4 and GaSe4 tetrahedra are connected to each other by vertex-sharing to form a three-dimensional framework with the counterion K+ residing in the cavities. Remarkably, all the NLO-active building units in the title compound are arranged in a completely parallel manner. Such a topological structure and the large susceptibility of the Hg–Se bonds enable the material to achieve good phase-matchability with a tremendous powder second harmonic generation (SHG) response at 2.09 μm that is about 20-times that of the benchmark material AgGaS2 (one of the largest responses among all the phase-matchable IR NLO chalcogenides reported to date). The optical band gap of KHg4Ga5Se12 was determined as 1.61 eV. Moreover, on the basis of the electronic band structure, the real-space atom-cutting analysis, the SHG-weighted electronic densities, and the local dipole moments calculations, the origin of the superior linear and nonlinear optical properties of the title compound is ascribed to the (Hg/Ga)­Se4 group. The calculated values for the maximum coefficient d 33 and birefringence (Δn) at 2.09 μm are −65.257 pm/V and 0.072, respectively. Such values agree well with experimental observations. Our study demonstrates that Hg-based metal chalcogenides are a class of IR NLO material with competitive features (good phase-matchability, very large SHG efficiency, wide transparency) desirable for practical applications.

The calculated formation energies indicate that CsBr(MAI)-terminated 2D perovskites are more stable than PbBr2(PbI2)-terminated 2D structures and an MAI-terminated monolayer could be even more stable than an MAPbI3 bulk.

Electrolysis of carbon dioxide to carbon monoxide, through which the greenhouse gas could be effectively utilized, using solid oxide electrolysis cells is now attracting much interest. Here, we show for the first time that the redox-stable Sr 2 Fe 1.5 Mo 0.5 O 6−δ (SFM) ceramic electronic-ionic conductor can be used as the electrocatalyst to electrolyze and convert 100% CO 2 to CO without using any safe gases like H 2 and CO. SFM maintained its cubic structure and had an electrical conductivity of 21.39 S cm −1 at 800 °C in 1:1 CO−CO 2 atmosphere. Its surface reaction coefficient for CO 2 reduction is 7.15 × 10 −5 cm s −1 at 800 °C. Compared with those reported for the typical oxide ceramic electrodes, high electrochemical performance has been demonstrated for single phase SFM cathode using 100% CO 2 as the feeding gas. For example, a current density of 0.71 A•cm −2 was obtained using a fuel cell supported on LSGM (La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3−δ ) electrolyte operated at 800 °C and an applied voltage of 1.5 V. The electrolysis performance was further improved by using SFM−Sm 0.2 Ce 0.8 O 2−δ composite cathode, and the current density increased to 1.09 A•cm −2 under the same operation conditions. Durability test at 800 °C for 100 h demonstrated a relatively stable performance for CO 2 electrolysis under harsh conditions of 100% CO 2 without safe gas and above 1 A cm −2 current density, which is seldom achieved in the literature but highly desirable for the commercial application, indicating that SFM is a highly promising ceramic fuel electrode for CO 2 electrolysis.