Dielectric and Piezoelectric Properties of NaNbO3-Based Solid Solutions

Detailed data are presented on the structure and electrical properties of Na_{1 – x} Li _x NbO₃ (0 x 0.145), Na_{1 – x} K _x NbO₃ (0 x 1.0), and (Na_{1 – x} Pb _x )(Nb_{1 – x} Ti _x )O₃ (0 x 1.0) solid solutions prepared by solid-state reactions followed by hot pressing. The sequences of phase changes and the stability ranges of the resulting phases are identified. The results are used to map out the compositional phase diagrams of the NaNbO₃-based binary systems.     

Anomalous High-Temperature Properties of BaPbO3-Based Solid Solutions

The thermal expansion, thermal stability, and electrical resistivity of the Ba_{1 – x} M _x Pb_{1 + y} O_{3 +} (M = Sr, Ca; 0 x 1.0, 0 y 0.2) and Ba_{1 – x} M" _x Pb_{1 – y} M" _y O_{3 +} (M" = K, La; M" = Sc, Sb; x, y= 0.01) ceramic materials were studied between 293 and 1073 K in air. The linear thermal expansion coefficient of the ceramics was found to increase abruptly at 700 K, from (10–14) × 10^–6K^–1in the range 300–600 K to (13–18) × 10^–6K^–1in the range 800–1000 K. The electrical resistivity of the ceramics passes through a sharp maximum near 750 K, with the largest jump in resistivity at the compositions Ba_0.6Sr_0.4PbO₃and Ba_0.9Ca_0.1PbO₃. The anomaly in thermal expansion is likely associated with the rearrangement of the lead–oxygen polyhedra in the structure of the solid solutions, and the jump in resistivity is attributable to changes in the average oxidation state of Pb ions in the surface layer of the ceramics.     

Doping Effects on the Properties of BaTiO3-Based Solid Solutions

The effect of Fe₂O₃ additions on the electrical properties and microstructure of yttria-doped barium titanate ceramics was studied by resistivity measurements and electron microscopy. Doping with 0.05 mol % Fe₂O₃ markedly increases the resistivity of the ceramics. The Fe atoms are nonuniformly distributed between BaTiO₃ and the grain-boundary phase Ba₆Ti₁₇O₄₀.     

Dielectric and Magnetic Properties of SrTiO3–BiMnO3 Solid Solutions

SrTiO₃–BiMnO₃ solid solutions with a cubic perovskite structure are synthesized in the range 30–70 mol % BiMnO₃. The solid solutions containing 60 and 70 mol % BiMnO₃ exhibit high dielectric losses in the microwave range and are, therefore, potential microwave absorbing materials. The real part of rf magnetic susceptibility of the sample containing 60 mol % BiMnO₃ lies in the range 2–3.     

Thermoelectric Properties of PbBi4Te7-Based Anion-Substituted Layered Solid Solutions

PbBi₄(Te_{1 – x} Se _x )₇ anion-substituted layered solid solutions (x = 0–0.2) are studied by x-ray diffraction and are shown to have the same 12-layer structure as PbBi₄Te₇, Their lattice parameters a and c decrease with increasingx. All of the alloys studied are n-type. Se substitution for Te reduces the electron concentration and lattice thermal conductivity and increases the thermoelectric power and electron mobility as compared to PbBi₄Te₇. Hall effect and resistivity measurements are carried out between 77 and 850 K, and the thermoelectric power and thermal conductivity are measured in the ranges 90–800 and 80–360 K, respectively.     

Effects of Bonding Configuration and Structural Perfection on the Properties of Doped NaNbO -Based Solid Solutions

The effects of bonding configuration (electronegativity) and doping-produced vacancies on the properties of doped NaNbO₃-based solid solutions were studied. The results demonstrate that there is an average electronegativity of the elements involved above which the uniform distortion parameter increases and the relative dielectric permittivity ^T ₃₃/₀decreases with increasing electronegativity, as is common in other solid-solution systems. Below this value, both and ^T ₃₃/₀vary in the opposite way. An explanation for the anomalous behavior of is proposed.     

Superior Energy Storage Properties and Optical Transparency in K0.5Na0.5NbO3-Based Dielectric Ceramics via Multiple Synergistic Strategies

Eco-friendly transparent dielectric ceramics with superior energy storage properties are highly desirable in various transparent energy-storage electronic devices, ranging from advanced transparent pulse capacitors to electro-optical multifunctional devices. However, the collaborative improvement of energy storage properties and optical transparency in KNN-based ceramics still remains challenging. To address this issue, multiple synergistic strategies are proposed, such as refining the grain size, introducing polar nanoregions, and inducing a high-symmetry phase structure. Accordingly, outstanding energy storage density (W_total ≈7.5 J cm⁻³, W_rec ≈5.3 J cm⁻³) and optical transmittance (≈76% at 1600 nm, ≈62% at 780 nm) are simultaneously realized in the 0.94(K_0.5Na_0.5)NbO₃-0.06Sr_0.7La_0.2ZrO₃ ceramic, together with satisfactory charge-discharge performances (discharge energy density: ≈2.7 J cm⁻³, power density: ≈243 MW cm⁻³, discharge rate: ≈76 ns), surpassing previously reported KNN-based transparent ceramics. Piezoresponse force microscopy and transmission electron microscopy revealed that this excellent performance can be attributed to the nanoscale domain and submicron-scale grain size. The significant improvement in the optical transparency and energy storage properties of the materials resulted in the widening of the application prospects of the materials.     

Optical Properties of Solid Pentacene

We have prepared pentacene films on Si, Al₂O₃, and glass substrates by thermal evaporation and have investigated their optical properties at room temperature over a wide range of frequencies from infrared to ultraviolet (5 meV to 6.5 eV). A series of optical phonon modes and electronic transitions have been observed. The internal vibrational modes in the infrared region match well their molecular counterparts but the electronic transitions show substantial changes from those of a free pentacene molecule. The HOMO–LUMO gap energy of the pentacene films deposited on Al₂O₃ and glass substrates is 1.85 eV.     

AIN-SiC固溶体的制备及介电性能

以碳化硅和铝粉为原料,均匀混合后在不同气氛中于2000℃下保温0．5h制得粉体。用X射线衍射分析（XRD）和扫描电子显微镜（SEM）对其进行表征。同时在8．2～12．4GHz频率范围内测试其介电性能。结果表明：在N2气氛中,当铝的含量较少时,未出现AIN物相,当铝含量超过10at%时,AIN相开始出现,并且AIN的含量随着铝含量的增加而增加。掺杂铝样品与未掺杂铝样品相比,其介电常数实部ε′和介电损耗tanδ皆降低,且随着铝含量的增加而逐步降低,主要是因为AIN具有较低的介电常数实部和损耗。     

Nonlinear Optical Properties of Porphyrins

Porphyrins and phthalocyanines have outstanding chemical and thermal stability. The macrocyclic structure and chemical reactivity of tetrapyrroles offers architectural flexibility and facilitates the tailoring of chemical, physical and optoelectronic parameters. The specific optical properties of the tetrapyrrole macrocycle combined with the synthetic methodologies now available and the already available theoretical and spectroscopic knowledge on their optical behavior make porphyrins a target of choice for this area. They are versatile organic nanomaterials with a rich photochemistry and their excited state properties are easily modulated through conformational design, molecular symmetry, metal complexation, orientation and strength of the molecular dipole moment, size and degree of conjugation of the π‐systems, and appropriate donor‐acceptor substituents. Here we review the structural chemistry and optical properties of recently synthesized porphyrin derivatives that offer potential for nonlinear optical (NLO) applications and complement existing studies on phthalocyanines. Classes of interest include the classic A₄ symmetric tetrapyrroles, while optimized systems include push‐pull porphyrins, oligomeric and supramolecular self‐assembled systems, films and nanoparticle systems, and highly conjugated porphyrin arrays.     

Electrical Properties of WO3-Based Ceramics

The electrical properties of WO₃ceramics with Na₂O, MnO₂, and Al₂O₃additions were investigated. The effects of postsintering heat treatment, electrode material, and NiO and Co₃O₄additions were examined.     

Effect of Bi_2O_3 Additive on the Microstructure and Dielectric Properties of BaTiO_3-Based Ceramics Sintered at Lower Temperature

High performance X8R dielectric ceramics were prepared by dopingBi2O3 to BaTiO3-based ceramics.The effect of small amounts(≤1.2 mol%) ofBi2O3 additive on the microstructure and dielectric properties of BaTiO3-based ceramics have been investigated.The Bi2O3 ,acting as a sintering additive,can effectively lower the sintering temperature of BaTiO3-based ceramics from 1300 to 1130 °C.The bulk density of BaTiO3-based ceramics increased and reached the maximum value with increasingBi2O3 content.The dielectric con...     

Laser Excitation Effect on the Optical and Dielectric Properties of Ferroelectric KNbO3 Single Crystals

The effects of laser irradiation on the optical absorption (200- to 800-nm range) and dielectric properties (10²- to 10⁷-Hz range) of KNbO₃ single crystals in ferroelectric phase have been studied. All these properties are found to be reduced significantly at lower frequencies with an increase in laser irradiation time. However, the phase transition temperature remains unchanged. It is observed that the dielectric constant (K) and loss (tan ) values of KNbO₃ single crystals are decreased significantly at room temperature or at Curie temperature by laser excitation. Appreciable changes in the band gap (eV) and activation energy are also observed after laser excitation.     

Thermodynamic Properties of ZnTe–CdTe Solid Solutions

The pseudobinary system ZnTe–CdTe was studied at 899 K by Knudsen cell mass spectrometric measurements. The vapor composition and pressure, ZnTe and CdTe activities, and Gibbs energy of mixing were determined. The results demonstrate that the composition dependences of CdTe and ZnTe activities exhibit, respectively, positive and negative deviations from ideality and that the Gibbs energy of mixing is lower than that of an ideal solution. The p–xsection along the pseudobinary join is constructed. At 899 K, a continuous series of solid solutions exists in the ZnTe–CdTe system, with no miscibility gap, and sublimation is incongruent. The composition dependence of 780-K CdTe activity suggests some evidence of phase segregation.     

SrTiO3为基的介质陶瓷的结构与介电性质

本文主要研究0.91(Sr_(0.84)Pb_(0.16))TiO_(?) 0.09(Bi_2O_3·3.5TiO_2)介质陶瓷的结构与介电性质。用扫描电镜和 X 射线衍射分析表明,此种材料在室温下为顺电立方相,具有晶粒小且均匀、致密度高等特点。介电测量表明,在10kHz～90MHz 范围内样品的介电常数ε′基本上保持不变,而介电常数ε″随频率的增加而平坦地增大。     

Preparation and Properties of ZnxCd1 – xSe Solid Solutions

ZnSe–CdSe substitutional solid solutions were prepared by isothermal diffusion over the entire composition range and characterized by x-ray diffraction and thermal analysis. The structure of the solid solutions was found to change from cubic to hexagonal between 30 and 40 mol % CdSe.     

二氧化钛薄膜的三阶非线性光学特性

采用脉冲激光沉积技术在熔石英基片上制备了c轴取向的锐钛矿相TiO₂薄膜.通过X射线衍射和原子力显微镜对薄膜的结构、结晶性和表面特性进行了表征.通过透射光谱计算得到TiO₂薄膜折射率约为2.1,光学带隙约为3.18eV.结合飞秒激光和Z扫描方法测量了薄膜的超快非线性光学特性,结果表明：锐钛矿TiO₂薄膜具有负的非线性吸收系数和负的非线性折射率,其大小分别为-6.2×10^-11m/W和-6.32×10^-17m²/W,对应的三阶非线性极化率的实部和虚部分别为-7.1×10^-11esu和-4.42×10^-12esu.并计算薄膜的优值比T=βλ/n₂≈0.8,表明锐钛矿相的TiO₂在非线性光学器件方面具有潜在的应用前景.