Crystal Growth, HOMO–LUMO Engineering, and Charge Transfer Degree in Perylene‑F_<i>x</i>TCNQ (<i>x</i> = 1, 2, 4) Organic Charge Transfer Binary Compounds

The methodologies of searching for novel organic charge transfer binary compounds and large-size crystal growth, in the case that only the two starting organic substances are known but the phase diagram is not known, the thermodynamic data of the binary compound are not known, and even the existence of new binary compounds is not known, were studied. Centimeter-long crystals of novel perylene-F₁TCNQ, perylene-F₂TCNQ, and perylene-F₄TCNQ charge transfer binary compounds are obtained from the gas phase. Kinetically lowering the sublimation rate is the key factor for growing large-size charge transfer compound single crystals. Changing the number of fluorine atoms in F_<i>x</i>TCNQ results in the variation of the electron affinity, which further changes the HOMO–LUMO of acceptor. Charge transfer degree is increased with increasing of fluorine atoms in the perylene-F_<i>x</i>TCNQ system. Therefore, the structure, stoichiometry, and kind of donor and acceptor enable HOMO–LUMO engineering of the charge transfer compound and tune the physical properties

Crystal Chemistry of Melilite [CaLa]₂[Ga]₂[Ga₂O₇]₂: a Five Dimensional Solid Electrolyte

Melilite-type [<i>A</i>₂]₂[<i>B</i>^I]₂[<i>B</i>^II₂O₇]₂ gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa]₂[Ga]₂[Ga₂O₇]₂, grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga₂O₇] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group <i>P</i>4̅2₁<i>m</i>(α, α, 0)­00<i>s</i>(α̅, α, 0)­000, α = 0.2160(5), with a subcell metric of <i>a</i> = 7.9383(2) Å, <i>c</i> = 5.2641(3) Å, onto which modulation vectors are superimposed: <i><b>q</b></i>_<b>1</b> = α (<i><b>a</b></i>* + <i><b>b</b></i>*), <i><b>q</b></i>_<b>2</b> = α (−<i><b>a</b></i>* + <i><b>b</b></i>*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible

Chiral Two-Dimensional Hybrid Organic–Inorganic Perovskites for Piezoelectric Ultrasound Detection

Hybrid organic–inorganic perovskites (HOIPs) have exhibited striking application potential in piezoelectric energy harvesting and sensing due to their high piezoelectricity, light weight, and solution processability. However, to date, the application of piezoelectric HOIPs in ultrasound detection has not yet been explored. Here, we report the synthesis of a pair of chiral two-dimensional piezoelectric HOIPs, R-(4-bromo-2-butylammonium)2­PbBr4 and S-(4-bromo-2-butylammonium)2­PbBr4 [R-(BrBA)2PbBr4 and S-(BrBA)2PbBr4], which show low mechanical strength and significant piezoelectric strain coefficients that are advantageous for mechanoelectrical energy conversion. Benefiting from these virtues, the R-(BrBA)2PbBr4@PBAT and S-(BrBA)2PbBr4@PBAT [PBAT = poly(butyleneadipate-co-terephthalate)] composite films show prominent underwater ultrasound detection performance with a transmission effectivity of 12.0% using a 10.0 MHz probe, comparable with that of a polyvinylidene fluoride (PVDF) device fabricated in the same conditions. Density functional theory calculations reveal that R-(BrBA)2PbBr4 and S-(BrBA)2PbBr4 have a beneficial acoustic impedance (5.07–6.76 MRayl) compatible with that of water (1.5 MRayl), which is responsible for the facile ultrasound-induced electricity generation. These encouraging results open up new possibilities for applying piezoelectric HOIPs in underwater ultrasound detection and imaging technologies

Polyaniline/CuO Nanoparticle Composites for Use in Selective H₂S Sensors

For ambient use, flexible hydrogen sulfide (H2S) gas sensors based on polyaniline (PANI) and copper oxide nanoparticles (CuO NPs) were investigated. PANI/CuO nanocomposites made by in situ (P-1) and bilayer (P-2) methods have shown high performances when sensing H2S of 0–25 ppm concentration in ambient conditions. The P-2 sensor maintained high sensitivity (S = 7.25) and excellent responsiveness (ΔRe = 188%). The P-1 sensor had high responses (<30 s), linearity (R2 = 99.5%), and stability, while the CuO NP sensor was especially sensitive (S = 13.5) within 0–10 ppm of H2S concentration. In addition, the flexible/conformable composite sensors had excellent H2S selectivity and bending stability. The enhancements of the composite sensors are mainly attributed to the PANI/CuO heterojunction formation that effectively reduced the PANI band gap from 2.51 eV (PANI) to 2.48 eV (P-1) and further down to 2.43 eV (P-2) for improved conductivity and charge-transport efficiency in the semiconductor network. The X-ray photoelectron spectroscopy analyses identified elements and valence band energy changes before and after H2S exposure. This study used facile methods for preparing nanocomposite-based gas sensors for the development of cost-effective, sensitive, conformable, durable, and ambient workable devices for monitoring fresh food quality in the food supply chain and environment safety for mining and petrochemical industry

Synthesis and Characterization of the Rare-Earth Hybrid Double Perovskites: (CH₃NH₃)₂KGdCl₆ and (CH₃NH₃)₂KYCl₆

Two hybrid rare-earth double perovskites, (CH₃NH₃)₂KGdCl₆ and (CH₃NH₃)₂KYCl₆, have been synthesized by a solution evaporation method and their structures determined by variable temperature single-crystal X-ray diffraction. The diffraction results show that at room temperature both perovskites adopt a rhombohedral structure with <i>R</i>3̅<i>m</i> symmetry, as found previously for (MA)₂KBiCl₆, and lattice parameters of <i>a</i> = 7.7704(5) Å and <i>c</i> = 20.945(2) Å for (MA)₂KGdCl₆ and <i>a</i> = 7.6212(12) Å and <i>c</i> = 20.742(4) Å for (MA)₂KYCl₆. Both phases exhibit a rhombohedral-to-cubic phase transition on heating to ∼435 K for (MA)₂KYCl₆ and ∼375 K for (MA)₂KGdCl₆. Density functional calculations on the rhombohedral phase indicate that both materials have large direct band gaps, are mechanically stable, and, in the case of (MA)₂KGdCl₆, could exhibit magnetic ordering at low temperatures

Synthesis, Crystal Structure, and Optical Properties of a Three-Dimensional Quaternary Hg–In–S–Cl Chalcohalide: Hg₇InS₆Cl₅

A crystalline three-dimensional (3D) quaternary chalcohalide, Hg₇InS₆Cl₅ (<b>1</b>), has been synthesized through a solid-state reaction under medium temperature. It is the first example in the family of the Hg–IIIA–Q–X (Q = S, Se, Te; X = F, Cl, Br, I) systems. Compound <b>1</b> features a 3D network and has an optical band gap of 2.54 eV

Crystallographic Correlations with Anisotropic Oxide Ion Conduction in Aluminum-Doped Neodymium Silicate Apatite Electrolytes

To better understand the oxide ion conduction mechanism of rare earth silicate apatites as intermediate temperature electrolytes for solid oxide fuel cells (SOFC), the effect of lower valent metal doping on the performance of Nd_{(28+<i>x</i>)/3}Al_<i>x</i>Si_6‑<i>x</i>O₂₆ (0 ≤ <i>x</i> ≤ 2) single crystals has been examined. The measurement of ionic conductivity via AC impedance spectroscopy showed that the conductivities were anisotropic and superior along the <i>c</i> direction. An interesting aspect from the impedance studies was the identification of a second semicircle with capacitance similar to that of a grain boundary component, despite the fact that polarized optical microscopy and electron backscattered diffraction showed that the single crystals consisted of a single grain. This semicircle disappeared after long-term (up to 3 months) annealing of the single crystals at 950 °C, also leading to a reduction in the bulk conductivity. In order to explain these observations, single-crystal X-ray diffraction studies were performed both before and after annealing. These studies found the undoped crystal conformed to <i>P</i>6₃/<i>m</i>, but with the O(3) oxygen positions, that participate in conduction, split nonstatistically across two sites with a shortened Si–O(3) bond. Consequently, the bond valence sum (BVS) of the Si (4.20) is larger than the formal valence. Fourier difference maps of the Al-doped crystals contain regions of excess scattering, suggesting the possible lowering of symmetry or creation of superstructures. After long-term annealing, the single crystal structure determinations were of higher quality and the experimental and nominal compositions were in better agreement. From these observations, we propose that in the as-prepared single crystals there are regions of high and low interstitial content (e.g., Nd_9.67Si₆O_26.5 and Nd_9.33Si₆O₂₆), and the second semicircle relates to the interface between such regions. On annealing, Nd redistribution and homogenization removes these interfaces and also reduces the number of interstitial oxide ions, hence eliminating this second semicircle while reducing the bulk conductivity. The results therefore show for the first time that the conductivity of apatite materials containing cation vacancies is affected by the thermal history

Cooperative Enhancement of Second-Harmonic Generation from a Single CdS Nanobelt-Hybrid Plasmonic Structure

Semiconductor nanostructures (<i>e</i>.<i>g</i>., nanowires and nanobelts) hold great promise as subwavelength coherent light sources, nonlinear optical frequency converters, and all-optical signal processors for optoelectronic applications. However, at such small scales, optical second-harmonic generation (SHG) is generally inefficient. Herein, we report on a straightforward strategy using a thin Au layer to enhance the SHG from a single CdS nanobelt by 3 orders of magnitude. Through detailed experimental and theoretical analysis, we validate that the augmented SHG originates from the mutual intensification of the local fields induced by the plasmonic nanocavity and by the reflections within the CdS Fabry–Pérot resonant cavity in this hybrid semiconductor–metal system. Polarization-dependent SHG measurements can be employed to determine and distinguish the contributions of SH signals from the CdS nanobelt and gold film, respectively. When the thickness of gold film becomes comparable to the skin depth, SHG from the gold film can be clearly observed. Our work demonstrates a facile approach for tuning the nonlinear optical properties of mesoscopic, nanostructured, and layered semiconductor materials

Crystallographic Correlations with Anisotropic Oxide Ion Conduction in Aluminum-Doped Neodymium Silicate Apatite Electrolytes

To better understand the oxide ion conduction mechanism of rare earth silicate apatites as intermediate temperature electrolytes for solid oxide fuel cells (SOFC), the effect of lower valent metal doping on the performance of Nd_{(28+<i>x</i>)/3}Al_<i>x</i>Si_6‑<i>x</i>O₂₆ (0 ≤ <i>x</i> ≤ 2) single crystals has been examined. The measurement of ionic conductivity via AC impedance spectroscopy showed that the conductivities were anisotropic and superior along the <i>c</i> direction. An interesting aspect from the impedance studies was the identification of a second semicircle with capacitance similar to that of a grain boundary component, despite the fact that polarized optical microscopy and electron backscattered diffraction showed that the single crystals consisted of a single grain. This semicircle disappeared after long-term (up to 3 months) annealing of the single crystals at 950 °C, also leading to a reduction in the bulk conductivity. In order to explain these observations, single-crystal X-ray diffraction studies were performed both before and after annealing. These studies found the undoped crystal conformed to <i>P</i>6₃/<i>m</i>, but with the O(3) oxygen positions, that participate in conduction, split nonstatistically across two sites with a shortened Si–O(3) bond. Consequently, the bond valence sum (BVS) of the Si (4.20) is larger than the formal valence. Fourier difference maps of the Al-doped crystals contain regions of excess scattering, suggesting the possible lowering of symmetry or creation of superstructures. After long-term annealing, the single crystal structure determinations were of higher quality and the experimental and nominal compositions were in better agreement. From these observations, we propose that in the as-prepared single crystals there are regions of high and low interstitial content (e.g., Nd_9.67Si₆O_26.5 and Nd_9.33Si₆O₂₆), and the second semicircle relates to the interface between such regions. On annealing, Nd redistribution and homogenization removes these interfaces and also reduces the number of interstitial oxide ions, hence eliminating this second semicircle while reducing the bulk conductivity. The results therefore show for the first time that the conductivity of apatite materials containing cation vacancies is affected by the thermal history

Crystallographic Correlations with Anisotropic Oxide Ion Conduction in Aluminum-Doped Neodymium Silicate Apatite Electrolytes

To better understand the oxide ion conduction mechanism of rare earth silicate apatites as intermediate temperature electrolytes for solid oxide fuel cells (SOFC), the effect of lower valent metal doping on the performance of Nd_{(28+<i>x</i>)/3}Al_<i>x</i>Si_6‑<i>x</i>O₂₆ (0 ≤ <i>x</i> ≤ 2) single crystals has been examined. The measurement of ionic conductivity via AC impedance spectroscopy showed that the conductivities were anisotropic and superior along the <i>c</i> direction. An interesting aspect from the impedance studies was the identification of a second semicircle with capacitance similar to that of a grain boundary component, despite the fact that polarized optical microscopy and electron backscattered diffraction showed that the single crystals consisted of a single grain. This semicircle disappeared after long-term (up to 3 months) annealing of the single crystals at 950 °C, also leading to a reduction in the bulk conductivity. In order to explain these observations, single-crystal X-ray diffraction studies were performed both before and after annealing. These studies found the undoped crystal conformed to <i>P</i>6₃/<i>m</i>, but with the O(3) oxygen positions, that participate in conduction, split nonstatistically across two sites with a shortened Si–O(3) bond. Consequently, the bond valence sum (BVS) of the Si (4.20) is larger than the formal valence. Fourier difference maps of the Al-doped crystals contain regions of excess scattering, suggesting the possible lowering of symmetry or creation of superstructures. After long-term annealing, the single crystal structure determinations were of higher quality and the experimental and nominal compositions were in better agreement. From these observations, we propose that in the as-prepared single crystals there are regions of high and low interstitial content (e.g., Nd_9.67Si₆O_26.5 and Nd_9.33Si₆O₂₆), and the second semicircle relates to the interface between such regions. On annealing, Nd redistribution and homogenization removes these interfaces and also reduces the number of interstitial oxide ions, hence eliminating this second semicircle while reducing the bulk conductivity. The results therefore show for the first time that the conductivity of apatite materials containing cation vacancies is affected by the thermal history