Enzhu Li

Structural, optical, and electrical properties of low-concentration Ga-doped CdO thin films by pulsed laser deposition

CdO thin films with low Ga doping concentrations were deposited on low-cost glass substrates by pulsed laser deposition. The influence of Ga doping concentration on structural, electrical, and optical properties of CdO thin films was studied. The Ga-doped CdO thin films show decreasing plasma wavelength and resistivity when increasing doping concentration, and the widening optical gap varies from 2.49 to 2.85xa0eV with the Ga doping concentration increasing from 0.2 to 1.2 at% due to Moss–Burstein effect. When Ga doping concentration in CdO thin films was controlled at low level from 0.6 to 1.0 at%, the films achieved both high conductivity (~10−4 Ω·cm) and high transmittance up to the infrared region (>1600xa0nm), which demonstrates good potential as an ideal transparent conductor of full-spectrum photovoltaic devices.

Preheating-assisted deposition of solution-processed perovskite layer for an efficiency-improved inverted planar composite heterojunction solar cell

Planar heterojunction perovskite solar cells have received a lot of attention due to their great potential, such as low-cost and rapidly improving performance. However, the poor fill surface coverage and numerous pinholes usually exist in the organic–inorganic hybrid perovskite layers, leading to undesirable electron–hole recombination. Herein, inverted cell structures based on NiOx/PCBM interfacial materials have been studied. A simple preheating method facilitates the formation of a relatively continuous and compact layer of well-crystallized CH3NH3PbI3−xClx perovskite by a one-step solution process, which can minimize film defects and thus improve the charge extraction dissociation and transport abilities at the interface. As a result, synchronized improvements in photovoltage (Voc), photocurrent (Jsc) and fill factor (FF) lead to ∼25% enhanced power conversion efficiency (PCE), compared to solar cells using conventional perovskite films. Our study highlights a simple and effective method to improve the perovskite film quality and the photovoltaic performance of inverted perovskite solar cells.

Improved Thermoelectric Performances of SrTiO3 Ceramic Doped with Nb by Surface Modification of Nanosized Titania

Nb-doped SrTiO3 ceramics doped with the surface modification of nanosized titania was prepared via liquid phase deposition approach and subsequent sintered in an Ar atmosphere. The surface modification of nanosized titania significantly improved the ratio of the electrical conductivity to thermal conductivity of SrTiO3 ceramic doped with Nb, and has little impact on the Seebeck coefficient, thus obviously improving the dimensionless thermoelectric figure of merit (ZT value). The surface modification of nanosized titania is a much better method to lower the thermal conductivity and to enhance the electrical conductivity than the mechanical mixing process of nanosized titania. The highest ZT value of 0.33 at 900xa0K was obtained. The reason for the improved thermoelectric performances by the surface modification of nano-sized titania was preliminary investigated.

Structural Evolution and Microwave Dielectric Properties of xZn0.5Ti0.5NbO4-(1–x)Zn0.15Nb0.3Ti0.55O2 Ceramics

Structure and microwave properties of xZn0.5Ti0.5NbO4-(1 - x)Zn0.15Nb0.3Ti0.55O2 ceramics in the range of x = 0.0-1.0 were investigated. Rietveld refinement analysis and Raman spectra show that rutile- and orthorhombic-type solid solutions formed at 0-0.2 and 0.65-1, a composite at 0.2-0.64. In the solid solution regions, chemical bonds are enlarged. In this case, the Zn/Ti/Nb-O1 bond covalency and bond susceptibility are reduced, and lattice energy and thermal expansion coefficient increase along with x increases, which is mainly responsible for the development of microwave dielectric properties. Furthermore, far-infrared spectra and a classical oscillator model were used to discuss the intrinsic dielectric properties in detail. Temperature stable ceramic was obtained for x = 0.516: εr ∼ 46.11, Q × f ∼ 27u202f031 GHz, and τf ∼ -1.51 ppm/°C, which is promising for microwave applications.

Low temperature sintering behavior of 11Li2O-3Nb2O5-12TiO2 microwave dielectric ceramics

AbstractLow temperature sintering behaviors, microstructures, and microwave dielectric properties of 11Li2O-3Nb2O5-12TiO2 (LNT) ceramics with Li2O-B2O3-SiO2 (LBS) glass additions were investigated. The XRD patterns reveal two phases, the “M-phase” and “ss-phase” Li2TiO3 solid solution phases. nThe results suggest that small amount of LBS glass could effectively decrease the sintering temperature of LNT ceramic from 1100 to 900xa0°C without reducing its microwave dielectric properties.n However, decrease in microwave dielectric properties of LNT ceramic occurred when excess LBS glass added. Typically, LNT ceramics with 0.5xa0wt.% LBS glass possessed excellent microwave dielectric properties: εrxa0=xa047.94, Qxa0×xa0fxa0=xa09290xa0GHz (fxa0=xa04.67xa0GHz), and τfxa0=xa049.63xa0ppm/°C were obtained when sintered at 900xa0°C.

Influence of SiO2 Addition on Properties of PTFE/TiO2 Microwave Composites

Composite substrates for microwave circuit applications have been fabricated by filling polytetrafluoroethylene (PTFE) polymer matrix with ceramic powder consisting of rutile TiO2 (D50xa0≈xa05xa0μm) partially substituted with fused amorphous SiO2 (D50xa0≈xa08xa0μm) with composition xxa0vol.% SiO2xa0+xa0(50xa0−xa0x)xa0vol.% TiO2 (xxa0=xa00, 3, 6, 9, 12), and the effects of SiO2 addition on characteristics such as the density, moisture absorption, microwave dielectric properties, and thermal properties systematically investigated. The results show that the filler was well distributed throughout the matrix. High dielectric constant (εrxa0>xa07.19) and extremely low moisture absorption (<0.02%) were obtained, resulting from the relatively high density of the composites. The ceramic particles served as barriers and improved the thermal stability of the PTFE polymer, retarding its decomposition. The temperature coefficient of dielectric constant (τε) of the composites shifted toward the positive direction (from −xa0309xa0ppm/°C to −xa0179xa0ppm/°C) as the SiO2 content was increased, while the coefficient of thermal expansion remained almost unchanged (∼xa035xa0ppm/°C).

Effects of surface fluoride-functionalizing of glass fiber on the properties of PTFE/glass fiber microwave composites

In this work, fluoride-functionalized glass fiber (F-GF) was prepared, in which glass fiber (GF) was modified with γ-methacryloxy propyltrimethoxy silane (γ-MPS), and then reacted with 2,2,2-trifluoroethyl methacrylate (TFEMA). Subsequently, PTFE/glass fiber microwave composites were prepared by incorporating 5 wt% of the GF, γ-MPS modified GF (M-GF) or F-GF into PTFE. The effect of F-GF on the mechanical and dielectric properties, as well as moisture absorption and coefficient of thermal expansion of the composites were investigated. The results show that fluorine is successfully grafted onto the surface of GF through –CF3 group, and F-GF forms a dense and compact interfacial structure with PTFE. The mechanical properties of PTFE/F-GF, including tensile strength (38.53 MPa) and elongation (226.82%), are obviously higher than those of PTFE/M-GF (34.73 MPa and 179.50%, respectively) and PTFE/GF (34.82 MPa and 174.33%, respectively). In addition, the PTFE/F-GF composite shows improved density (2.174 g cm−3), dielectric constant (2.18), and decreased dielectric loss (0.0009), moisture absorption (0.008%) and temperature coefficient of dielectric constant (−18.6 ppm per °C). The conclusions demonstrate that the method of surface fluorination of glass fibers offers promising application in PTFE based microwave materials.

Photocatalytic activity of attapulgite–TiO 2 –Ag 3 PO 4 ternary nanocomposite for degradation of Rhodamine B under simulated solar irradiation

An excellent ternary composite photocatalyst consisting of silver orthophosphate (Ag3PO4), attapulgite (ATP), and TiO2 was synthesized, in which heterojunction was formed between dissimilar semiconductors to promote the separation of photo-generated charges. The ATP/TiO2/Ag3PO4 composite was characterized by SEM, XRD, and UV-vis diffuse reflectance spectroscopy. The co-deposition of Ag3PO4 and TiO2 nanoparticles onto the surface of ATP forms a lath-particle structure. Compared with composite photocatalysts consisting of two phases, ATP/TiO2/Ag3PO4 ternary composite exhibits greatly improved photocatalytic activity for degradation of rhodamine B under simulated solar irradiation. Such ternary composite not only improves the stability of Ag3PO4, but also lowers the cost by reducing application amount of Ag3PO4, which provides guidance for the design of Ag3PO4- and Ag-based composites for photocatalytic applications.

Structure and microwave dielectric properties of Zn 0.9 Mg 0.1 TiO 3 –Zn 0.15 Nb 0.3 Ti 0.55 O 2 ceramics with ZnO–B 2 O 3 –SiO 2 glass

Abstract(1u2009−u2009x)Zn0.9Mg0.1TiO3–xZn0.15Nb0.3Ti0.55O2 ((1u2009−u2009x)ZMT–xZNT) (xu2009=u20090.100, 0.125, 0.150, 0.175, 0.200) ceramics were prepared at 900xa0°C by conventional mixed-oxide method. The phase content, microstructure and microwave dielectric properties had been investigated in detail. Rietveld refinement shows the coexistence of Zn0.9Mg0.1TiO3, Zn0.15Nb0.3Ti0.55O2, Zn(BO2)2 and Zn2TiO4 phases. With ZnO–B2O3–SiO2 (ZBS) glass added, the ceramics can be sintered well at 900xa0°C with a smaller grain size of 0.12xa0µm and a higher relative density (>u200995%). The microwave dielectric properties are largely influenced by the phase composition according to mixture rule. A typical sample of 0.825ZMT–0.175ZNT ceramic with optimal dielectric properties (εru2009=u200926.14, Qu2009×u2009ƒu2009=u200927184xa0GHz, τƒu2009=u2009−u20093.46xa0ppm °C−1) was sintered at 900xa0°C for 4xa0h.

Effects of (Na1/2Nd1/2)TiO3 on the microstructure and microwave dielectric properties of PTFE/ceramic composites

A study on polytetrafluoroethylene (PTFE) composites with Na1/2Nd1/2TiO3 (NNT) ceramic and E glass shorten fiber (E-GF) was described. The E-GF content was fixed at 5 wt.%, and the NNT content varied from 12.1 vol.% to 42.8 vol.%. This paper systematically introduced the preparation process of composites and the effects of NNT filling content on the properties of composites. The surface modification of ceramic powders was observed by Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), which proved that NNT surfaces have been modified by Perfluorooctyltriethoxysilane (F8261) successfully. When the NNT filling content was 42.8 vol.%, substrate material with a low water absorption of 0.12%, high dielectric constant of 9.45, low dielectric loss of 0.0024, and τε of -222xa0ppm/°C were achieved, which is of great reference significance for the miniaturization and integration of microwave devices.