PbX(X=S,Se)纳米结构材料的制备方法

PbX(X=S,Se)纳米结构材料因其良好的光电性能,在太阳能电池等方面有着较好的应用前景,目前已成为半导体领域的研究热点.概括和总结了几种制备PbX纳米材料的经典和新型方法,其中包括水热法、溶剂热法、化学气相沉积法、中孔材料模板法、熔盐籽晶法、纳米晶的取向附属物法和微波法等,并分析和讨论了各方法的特点及对应产物的特征.     

Time‐Dependent Mechanical Response of APbX3 (A = Cs,CH3NH3; X = I,Br) Single Crystals

The ease of processing hybrid organic–inorganic perovskite (HOIPs) films, belonging to a material class with composition ABX₃, from solution and at mild temperatures promises their use in deformable technologies, including flexible photovoltaic devices, sensors, and displays. To successfully apply these materials in deformable devices, knowledge of their mechanical response to dynamic strain is necessary. The authors elucidate the time‐ and rate‐dependent mechanical properties of HOIPs and an inorganic perovskite (IP) single crystal by measuring nanoindentation creep and stress relaxation. The observation of pop‐in events and slip bands on the surface of the indented crystals demonstrate dislocation‐mediated plastic deformation. The magnitudes of creep and relaxation of both HOIPs and IPs are similar, negating prior hypothesis that the presence of organic A‐site cations alters the mechanical response of these materials. Moreover, these samples exhibit a pronounced increase in creep, and stress relaxation as a function of indentation rate whose magnitudes reflect differences in the rates of nucleation and propagation of dislocations within the crystal structures of HOIPs and IP. This contribution provides understanding that is critical for designing perovskite devices capable of withstanding mechanical deformations.     

Synthesis and crystal structures of a new (2,3-(CH3)2C6H3NH3)H2XO4 (X=P,As)

The aim of encapsulation of 2,3-dimethylanilinium cation in (H₂XO₄)_n polymeric anion chains is to build acentric frameworks that are efficient for non-linear optical (NLO) applications. The synthesis and structures of two new inorganic–organic NLO crystals with general formula (2,3-(CH₃)₂C₆H₃NH₃)H₂XO₄ (X=P, As) are reported. The magnitude of their second harmonic generations (SHG) responses was found to be between the KDP and urea. They crystallize with monoclinic unit-cells and are isotopic. We have determined the structure of phosphoric salt. The following unit-cell parameters were found: a=8.866(3) Å, b=5.909(6) Å, c=10.644(5) Å, β=112.44(1)°, V=515.5(5) Å³ and D_X=1.412 g cm⁻³. The space group is P2₁ with Z=2. The structure was refined with R=0.041 (R_w=0.057) for 1652 reflections with I≥3σ(I). It exhibits infinite (H₂PO₄)_nⁿ⁻ chains. The organic groups (2,3-(CH₃)₂C₆H₃NH₃)⁺ are anchored between adjacent polyanions through multiple hydrogen bonds. Chemical preparation, crystal structure, calorimetric and spectroscopic investigation are described.     

Amino acid 2-aminopropanoic CH3CH(NH2)COOH crystals: materials for photo- and acoustoinduced optoelectronic applications

Photo-induced treatment of l-alanine single crystals grown by slow evaporation method at an ambient temperature was performed using a 25 ps Nd:YAG pulsed laser in the presence of an external acoustic filed. The changes of the absorption were studied for the wavelength 265 nm near the energy band gap edge at acoustical power density varying within 4–6 W/cm². The observed absorption changes indicate that the external optical electric field strengths and acoustical power densities may be efficient parameters for the characterization of photo-optical and acousto-optical treatment of the samples. From the X-ray diffraction data we have optimized the atomic positions assuming that force on the atoms is around 1 mRy/au. These are used to calculate the electronic structure and the chemical bonding for the amino acid l-alanine single crystals. The calculated electronic band structure and densities of states confirms the experimental results that this compound possesses a relatively large energy band gap. The upper valence band has its maximum at the Z point of the Brillouin zone while the conduction band minimum is located at Γ point in the zone center, resulting in an indirect energy band gap. The electronic energy gap is equal to 4.19 eV within a framework of the used local density approximation and 4.54 eV with the Engel–Vosko generalized gradient approximation as the exchange correlation potential. This is in an agreement with our experimentally measured energy band gap ~4.67 eV. The existence of O-p character in the upper valence band has a significant consequence for the optical band gap. From our calculated electron charge density distribution, we obtain a space electron charge density distribution in the average unit cell of the crystal. The chemical bonding features of l-alanine amino acid were analyzed.     

Conduction mechanism in composite solid electrolytes,PbX 2-Al2O3 (X = Cl,Br, l) systems

Composite solid electrolytes PbX ₂-Al₂O₃ (X=Cl, Br, l) have been synthesized by the powder metallurgical process, and investigated by complex impedance analysis. X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscope (SEM) techniques. The phase analyses reveal that the composites are two-phase systems. No chemical reaction nor solid solution formation takes place between Al₂O₃ and the respective matrix phases. SEM photomicrographs show that Al₂O₃ particles are uniformly dispersed in the matrix phase for various systems. While PbCl₂-Al₂O₃ and PbBr₂-Al₂O₃ composites show a decrease in conductivity over their respective pure phases; Pbl₂-Al₂O₃ composites exhibit enhanced conductivity. By using the known diffusion and mobility data of the mobile species it has been shown that enhancement in conductivity is possible only in case of Pbl₂.     

The mechanical properties of (SN)X single crystals

The compression stress-strain behaviour of single crystals of sulphur nitride, (SN)_x, a metallic polymer, was measured in the ambient environment. Measurements were made both parallel and perpendicular to the chain axis on crystals which were about 1 mm in size. The plastic stress-strain behaviour resembled that of a highly anisotropic metal. Deformation to large strains produced a fibrilated structure which graphically exhibits the polymeric nature of (SN)_x. Young's moduli parallel and perpendicular to the chain were 21 and 1.4 GPa respectively. An analysis of the possible slip systems in (SN)_x indicated that there is only one easy glide system, (1 0 0) [0 0 1].Supported by the National Science Foundation MRL Program under Grant No. DMR 76-80994.     

Near-infrared combination and overtone bands of the CH2 sequence in CH2X2, CH2XCHX2, and CH3(CH2)5CH3 and their characteristic frequency zones

We characterized near-infrared spectra of the CH2 sequence in CH2X2 (X=halogen), CH2ClCHCl2, and CH3(CH2)5CH3. Each near-infrared absorption in the region from 3500 to 10,000 cm-1 is consistently assigned to one of the five different combination or overtone groups, in the order of increasing frequency, of the {[v(CH)]+[delta(CH)]} (A), {[v(CH)]+[2delta(CH)]} (B), [2v(CH)] (C), {[2v(CH)]+[delta(CH)]} (D), and [3v(CH)] (E) types, where v(CH) and delta(CH) denote the CH stretching and CH deformation normal modes, respectively. Each group has its own characteristic frequency zone. The bands of B, D, and E, which are second-order combinations or overtones, are weaker by 1/10-1/50 than those of A and C, which are first-order combinations or overtones. The near-infrared spectra of the CH2 sequence show "window zones" of very weak or no absorptions. This suggests that we can perceive the characteristic near-infrared bands of a functional group through the window zones, and we give an example to demonstrate this. The first-order combination bands of type A only of CH2X2 are reasonably assigned to a pair of the normal modes of v(CH) and delta(CH). From this we predict that the first-order combination bands should give structural information on the CH2 chain, similar to the infrared fundamental bands.     

0D Cs3Cu2X5 (X = I,Br, and Cl) Nanocrystals: Colloidal Syntheses and Optical Properties

0D lead‐free metal halide nanocrystals (NCs) are an emerging class of materials with intriguing optical properties. Herein, colloidal synthetic routes are presented for the production of 0D Cs₃Cu₂X₅ (X = I, Br, and Cl) NCs with orthorhombic structure and well‐defined morphologies. All these Cs₃Cu₂X₅ NCs exhibit broadband blue‐green photoluminescence (PL) emissions in the range of 445–527 nm with large Stokes shifts, which are attributed to their intrinsic self‐trapped exciton (STE) emission characteristics. The high PL quantum yield of 48.7% is obtained from Cs₃Cu₂Cl₅ NCs, while Cs₃Cu₂I₅ NCs exhibit considerable air stability over 45 days. Intriguingly, as X is changed from I to Br and Cl, Cs₃Cu₂X₅ NCs exhibit a continuous redshift of emission peaks, which is contrary to the blueshift in CsPbX₃ perovskite NCs.     

Optical properties of three-dimensional P(St-MAA) photonic crystals on polyester fabrics

The three-dimensional (3D) photonic crystals with face-centered cubic (fcc) structure was fabricated on polyester fabrics, a kind of soft textile materials quite different from the conventional solid substrates, by gravitational sedimentation self-assembly of monodisperse P(St-MAA) colloidal microspheres. The optical properties of structural colors on polyester fabrics were investigated and the position of photonic band gap was characterized. The results showed that the color-tuning ways of the structural colors from photonic crystals were in accordance with Bragg’s law and could be modulated by the size of P(St-MAA) colloidal microspheres and the viewing angles. The L¹a¹b¹ values of the structural colors generated from the assembled polyester fabrics were in agreement with their reflectance spectra. The photonic band gap position of photonic crystals on polyester fabrics could be consistently confirmed by reflectance and transmittance spectra.     

Photostriction of CH3NH3PbBr3 Perovskite Crystals

Organic–inorganic hybrid perovskite materials exhibit a variety of physical properties. Pronounced coupling between phonon, organic cations, and the inorganic framework suggest that these materials exhibit strong light–matter interactions. The photoinduced strain of CH₃NH₃PbBr₃ is investigated using high‐resolution and contactless in situ Raman spectroscopy. Under illumination, the material exhibits large blue shifts in its Raman spectra that indicate significant structural deformations (i.e., photostriction). From these shifts, the photostrictive coefficient of CH₃NH₃PbBr₃ is calculated as 2.08 × 10^?8 m² W^?1 at room temperature under visible light illumination. The significant photostriction of CH₃NH₃PbBr₃ is attributed to a combination of the photovoltaic effect and translational symmetry loss of the molecular configuration via strong translation–rotation coupling. Unlike CH₃NH₃PbI₃, it is noted that the photostriction of CH₃NH₃PbBr₃ is extremely stable, demonstrating no signs of optical decay for at least 30 d. These results suggest the potential of CH₃NH₃PbBr₃ for applications in next‐generation optical micro‐electromechanical devices.     

A zinc phosphate, [NH3(CH2)3NH3][Zn4(PO4)2(HPO4)2], possessing alternate inorganic and organic layers

A new zinc phosphate of the formula, [NH₃(CH₂)₃NH₃][Zn₄(PO₄)₂(HPO₄)₂], has been synthesized hydrothermally starting from a zinc amine complex. It crystallizes in the monoclinic space group C2/c; a=17.279(1), b=5.193(1), c=20.115(1) Å, β=92.6(1)°; V=1803.1(2) ų; Z=4; D_calc=2.05 g cm⁻³; μ (MoKα)=5.62 mm⁻¹. The final R, and wR₂=0.037, 0.093 obtained for 136 observed data [I>2σ(I)]. The structure consists of macroanionic sheets of interconnected ZnO₄ and PO₄ tetrahedra in the ab plane. The sheets are held together by hydrogen bond interactions with the organic structure-directing amine, forming alternate inorganic–organic layers in this material. Hydrogen bond interactions between the inorganic layers, via the terminal –OH group, leads to the formation of pseudo one-dimensional channels.     

Optical properties of some laser crystals

 In the following work the results of temperature dependence refractive indices measurements, thermooptical coefficients and dispersion in a wide range of temperature are presented. For measurements of refractive indices the least deviation method was employed. The measurements were carried out in the temperature region of 20–800° C for BBO crystals and 20–600° C for LBO crystals. It is revealed that the character of the refractive indices change in these crystals is different although the refractive indices of both crystals decrease while temperature increases. Whereas the temperature dependence of refractive indices in Ba B₂O₄ is practically linear, the same temperature dependence in LiB₃O₅ has more complicated character. It contains some particular features of refractive indices dispersion and thermooptical coefficients. Received: 11 January 1999/Reviewed and accepted: 15 January 1999