RESUMO
Second-harmonic-generation (SHG) switching is an emerging phenomenon with potential applications in bistable storage and optical switches while also serving as a sensitive probe for inversion-symmetry. Temperature-induced disorder-order phase transition has been proven to be a rational design strategy for achieving SHG bi-state switching; however, pressure-sensitive SHG switching via a disorder-order structural transition mechanism is rarely reported and lacks sensitivity and cyclicity as practical switching materials. Herein, we demonstrate the pressure-induced "dynamical disorder-order" phase transition as an effective strategy for triggering SHG and SHG switching in NH4Cl. The "dynamical disorder-order" phase transition of NH4Cl occurring at as low as 1 GPa is confirmed by comprehensive in situ high-pressure XRD, molecular vibrational spectra, and Brillouin scattering spectra. The pressure-induced SHG is responsive to a wide excitation wavelength region (800-1500 nm), and the "off-on" switching is reversible for up to 50 cycles, setting a record for pressure-driven switching materials. It is worth noting that when pressure is further increased to 14 GPa, NH4Cl exhibits another SHG "on-off" switching, which makes it the first triplet SHG "off-on-off" switching material. Molecular dynamics simulations reveal the key role of N-H···Cl hydrogen bonding in the pressure-induced "dynamic disorder-order" mechanism. Finally, we verified that chemical pressure and physical pressure can jointly regulate the SHG switching behavior of NH4X (X = Cl, Br). The pressure-driven "dynamic disorder-order" transition mechanism sheds light on the rational design of multistable SHG switching materials for photoswitches and information storage.
RESUMO
A novel zeolite-like topology oxonitridosilicate La3.6Ba1.7Si5N10O2.1 with the space group Amm2 (no. 38) and lattice parameters a = 9.5193 (3) Å, b = 16.7011 (5) Å, c = 26.0279 (8) Å, and Z = 12 has been synthesized by a high-temperature solid-state reaction. The crystal structure of La3.6Ba1.7Si5N10O2.1 has four different kinds of tiling, and the cages in the structure are filled with La, Ba, and O atoms. The presence of a noncentrosymmetric space group further suggests its potential for nonlinear optical (NLO) applications, and La3.6Ba1.7Si5N10O2.1 demonstrated a stronger second-harmonic generation (SHG) response than that of SiO2.
RESUMO
Negative thermal expansion (NTE) and zero thermal expansion (ZTE) properties are of great significance for the long-life stable operation of precision equipment. However, there are still existing challenges in finding new materials that exhibit NTE or ZTE over a wide temperature range. Here, we report negative, zero, and positive thermal expansion in NiAs-type, defective Cr1-δTe, containing three compounds: hexagonal CrTe, monoclinic Cr3Te4, and trigonal Cr5Te8. CrTe shows the NTE behavior from 280 to 340 K with the volume coefficient of thermal expansion αV = -27.6 × 10-6 K-1. Cr3Te4 shows the ZTE behavior over a wide temperature range of 180-320 K (αV = 0.16 × 10-6 K-1). And Cr5Te8 holds the PTE behavior over the whole temperature range (αV = 38.5 × 10-6 K-1). All of the samples show obvious anisotropic thermal expansion on heating. Combined with the magnetic measurements, it can be confirmed that the NTE and ZTE properties in ferromagnetic Cr1-δTe originate from the magnetovolume effect (MVE). Such NiAs-type, defective compounds with similar compositions but different structures provide a new perspective for tuning the NTE properties of materials and searching for new materials with ZTE over a wide temperature range.