Papers by Author: Zhi Jian Peng

Abstract: Microwave dielectric ceramics with a nominal composition of 0.95MgTiO₃-0.05CaTiO₃- xPrAlO₃ (x=0-0.015) were prepared by conventional solid-state sintering. The phase composition, microstructure and dielectric properties were characterized by X-ray diffractometer, scanning electron microscope and vector network analyzer, respectively. A two-phase system with major MgTiO₃ phase and minor CaTiO₃ phase was detected. With increasing content of PrAlO₃, the grain size of the obtained ceramics decreased; the dielectric constant and quality factor increased first and then decreased. The temperature coefficient of resonant frequency decreased after PrAlO₃ was doped, but with more PrAlO₃ doped it will increase. The obtained 0.95MgTiO₃-0.05CaTiO₃ ceramic doped by PrAlO₃ with x=0.0075 presented the best performance with ε_r=19.04, Q·f=42400 GHz and τ_f=-19.40 ppm/°C.

Abstract: A series of oxygen-deficient tin oxide thin films were deposited by radio frequency magnetron sputtering a sintered tin oxide ceramic target under pure argon atmosphere at different sputtering powers (80-160 w) under the based pressure of no more than 2.0×10^-4 Pa, sputtering pressure of 2.0 Pa and deposition time of 20 min. It was revealed that all the as-deposited films were oxygen-deficient tin oxide films, and the main defect in films was oxygen vacancy (V_O), whose concentration gradually decreased with the increase of sputtering power. The films prepared at a power of no more than 120 w were amorphous, and as the sputtering power increased to 140 and 160 w, the deposited thin films exhibited polycrystalline characteristics with (110), (101) and (211) diffraction peaks of tin oxide. The grain size, deposition rate as well as thickness of the obtained films rose up with increasing sputtering power. In addition, as the sputtering power raised, the electrical resistivity of the films increased, due to the electron conducting mechanism controlled by V_O in the samples.

Abstract: Novel multipods-branched Cd-Se-S micro-/nanostructures (MNSs) were successfully prepared in a tube furnace by thermal evaporation under atmospheric pressure through using high-purity CdS and CdSe mixture powder with a molar ratio of 1:1 as evaporation source, high-purity Ar gas as carrier and protective gas, and mica wafer as substrate. Under the optimum condition, the evaporation temperature was 1100 °C, Ar gas flow rate was 200 sccm, and the distance between the evaporation source and substrate was 22 cm. The microstructure examination revealed that the length of the obtained branches was up to tens of microns and the diameter of the branches was of a few microns. The composition and crystal structure analyses indicated that, the chemical composition of the multipods-branched Cd-Se-S MNSs was CdSe_0.86S_0.14, which had a hexagonal structure and good crystallinity. The photoluminescence spectrum at room temperature displays an intrinsic emission peak around 620 nm. In addition, their growth might be controlled by a vapor-solid mechanism.

Abstract: In this work, the photoelectric properties of ZnO_1-x/graphene heterostructures were investigated. Such ZnO_1-x/graphene heterostructures were constructed from non-stoichiometric zinc oxide (ZnO_1-x) film and graphene by first depositing ZnO_1-x layer through radio frequency magnetron sputtering onto silicon wafers with SiO₂ layer and then transferring graphene via a wet method. It was revealed that such heterostructures could have improved photoelectric properties. Compared with ZnO_1-x films, the absorbance of the ZnO_1-x/graphene heterostructures in visible and near-infrared region was enhanced; and due to the high conductivity of graphene, the photocurrent was significantly enhanced both in dark and under irradiation of a 700 nm light. By calculating the absolute current gain, it was revealed that the fabricated ZnO_1-x/graphene heterostructures would have a higher current gain. Thus, such ZnO_1-x/graphene heterostructures would be promisingly applied in visible light to near-infrared detection devices.

Abstract: TiCN-based cermets were prepared by hot-press sintering through adding various amounts of AlN nanopowder (0-20 wt.%) into a 64 wt.% TiC_0.5N_0.5-10 wt.% WC-8.5 wt.% Mo-12.5 wt.% Ni-5 wt.% Co system. The microstructure and mechanical properties of the prepared cermets were investigated. For the prepared cermets, samples with 5 wt.% AlN nanopowder exhibited optimum mechanical properties of Vickers hardness 2191 HV₁₀, bending strength 601 MPa, and fracture toughness 6.03 MPa.m^1/2, respectively.

Abstract: In this work, we fabricated ZrB₂-SiC-ZrSi₂ composites containing different fractions (0.5-5 vol.%) of ZrSi₂ by spark plasma sintering at 1600 °C under a uniaxial pressure of 30 MPa. The addition effect of ZrSi₂ on the composition, microstructure and mechanical properties of the composites were investigated. The results indicated that the densification of ZrB₂-SiC-ZrSi₂ composites could be enhanced along with the increase of the added fraction of ZrSi₂, with its relative density reaching the maximum of about 85.6% when 3 vol.% of ZrSi₂ was added. The hardness of the composites would decrease after the addition of ZrSi₂ in the range of 960-1200 HV₅. The flexural strength initially increased and then decreased with the addition of ZrSi₂, reaching a maximum of about 330 MPa when 3 vol.% of ZrSi₂ was added.

Abstract: In order to investigate the influence of (Bi_0.5M_0.5)TiO₃ (M=Li, Na, K, Rb) addition on the Curie temperature (T_c) and positive temperature coefficient (PTC) effect of BaTiO₃-based ceramics, BaTiO₃-(Bi_0.5M_0.5)TiO₃ (M=Li, Na, K, Rb) solid solutions were prepared by a conventional solid sintering reaction using high-purity reagents. It was found that the T_c of the samples would vary with (Bi_0.5M_0.5)TiO₃ of different alkali ions, in which BT-BKT ceramics had the highest value (about 148 °C). Moreover, the incorporation of alkali ions would influence the PTC effect of the sample, which can be defined by the resistivity jump with the ratio of maximum to minimum resistivity (ρ_max/ρ_min). Under the present conditions, the ρ_max/ρ_min of BT-BRT and BT-BLT ceramics were almost equal and higher than those of BT-BNT and BT-BKT ceramics.

Abstract: ZnO_1-x thin films were deposited by RF magnetron sputtering on conducting silicon wafers at room temperature with ZnO_n (n≤1) target under an atmosphere of O₂/Ar ratio varying from 0 to 2.0. The correlation between composition, structure and electrical resistivity of the obtained films was investigated. X-ray diffraction analysis revealed that the prepared würtzite ZnO_1-x films had c-axis preferential growth orientation. When the O₂/Ar ratio was lower than 0.5, the main form of defects in the films was oxygen vacancy; when it was 0.5, the composition of the film approached to the stoichiometric ZnO and had the least number of defects; after that, the main type of defects in the films was interstitial zinc. Thus, with increasing O₂/Ar ratio, the electrical resistivity of the films increased first and then decreased.

Abstract: MoO₂ has been widely used in many fields such as catalyst, gas-senor, super capacitor and Li-ion battery electrode. In this paper, MoO₂ nanoplates were synthesized in high density and large scale on silicon substrates via simple thermal evaporation of MoO₃ and S powders at 950 °C in a tube furnace. The morphology, composition and structure of the nanoplates were characterized by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results indicate that the as-synthesized nanoplates are of well crystalline structure, and the thickness of these nanoplates is in the range of 100-300 nm. The growth mechanism of the nanoparticles was proposed as a vapor-solid process.

Abstract: WO₃ particles with different grain sizes were prepared by a thermal evaporation method. The composition, morphology, and optical properties of the samples were analyzed by powder X-ray diffraction, scanning electron microscopy, and UV–vis absorption and photoluminescence spectroscopy. Their photocatalytic properties were evaluated by decomposing methylene blue in aqueous phase. It was found that the smaller the grain size of the prepared WO₃ particles, the better the degradation effect on methylene blue.