Unusual Electrical Transport Characteristic of the SrSnO3/Nb-Doped SrTiO3 Heterostructure

Depeng Wang,Ruifeng Niu,Liqi Cui,Weitian Wang 한국재료학회 2023 한국재료학회지 Vol.33 No.6

An all-perovskite oxide heterostructure composed of SrSnO3/Nb-doped SrTiO3 was fabricated using the pulsed laser deposition method. In-plane and out-of-plane structural characterization of the fabricated films were analyzed by x-ray diffraction with θ-2θ scans and φ scans. X-ray photoelectron spectroscopy measurement was performed to check the film’s composition. The electrical transport characteristic of the heterostructure was determined by applying a pulsed dc bias across the interface. Unusual transport properties of the interface between the SrSnO3 and Nb-doped SrTiO3 were investigated at temperatures from 100 to 300 K. A diodelike rectifying behavior was observed in the temperature-dependent current-voltage (IV) measurements. The forward current showed the typical IV characteristics of p-n junctions or Schottky diodes, and were perfectly fitted using the thermionic emission model. Two regions with different transport mechanism were detected, and the boundary curve was expressed by ln I = -1.28V - 13. Under reverse bias, however, the temperature- dependent IV curves revealed an unusual increase in the reverse-bias current with decreasing temperature, indicating tunneling effects at the interface. The Poole-Frenkel emission was used to explain this electrical transport mechanism under the reverse voltages.

Low-temperature dielectric and impedance properties of SrSn0.2Ti0.8O3 ceramics

Depeng Wang,Ruifeng Niu,Liqi Cui,Weitian Wang 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.3

Tin-doped and undoped perovskite SrTiO3 ceramics were synthesized by solid-state reaction method using SrCO3, TiO2 andSnO2 powders as raw materials. When the samples sintered at 1400 ℃, the SrSn0.2Ti0.8O3 and SrTiO3 ceramics all crystallizedin cubic structures. The lattice parameters of SrSn0.2Ti0.8O3 are slightly larger than that of SrTiO3 due to the bigger size ofSn4+ ions. The frequency-dependent dielectric and impedance properties of SrSn0.2Ti0.8O3 ceramics were investigated in thetemperature range of 300-100 K. The obtained value of low-temperature dielectric permittivity is larger than 10000, and thatof dielectric loss is lower than 0.018 at f = 1 kHz. The impedance spectra were used to show the grains and grain boundarieseffects in SrSn0.2Ti0.8O3 ceramics. The calculated electrical conductivity demonstrates the semiconductor properties of theprepared samples. The results indicate that SrSn0.2Ti0.8O3 ceramics have potential applications in dielectric and electronicdevices.

Effect of A- and B-site doping on the low-temperature dielectric and impedance properties of BaTiO3-based ceramics

Niu Ruifeng,Wang Depeng,Cui Liqi,Wang Weitian 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.6

In this work, two series of BaTiO3-based ceramics, Ba1-xSrxTiO3 (x=0, 0.2, 0.4, 0.6, 0.8) and BaTi1-xTaxO3 (x=0.03, 0.06, 0.075, 0.09, 0.1), were synthesized by using standard solid-state reaction method. Frequency-dependent dielectric and impedance properties were investigated in low temperature range of 300–100 K. The changes in dielectric properties of Ba1-xSrxTiO3 are believed to originate from the phase transition due to the diferent A-site Sr2+ doping concentration. The local electron-pinned defect-dipole efect is responsible for the enhancement of dielectric constant observed in B-site Ta5+ doped BaTi1-xTaxO3 ceramics. The complex impedance analysis was used to discern the temperature and frequency dependence of grains and grain boundaries responses. The results suggest the application of A- and B-site doped BaTiO3 ceramics in the feld of dielectric devices at low temperatures.

Removal of Cr(VI) from aqueous solution by rice husk derived magnetic sorbents

Ruifeng Yang,Shangru Zhai,Yuan Fan,Zhimin Lei,Na Liu,Jialiang Lv,Bin Zhai,Lei Wang 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.4

−A novel magnetic porous sorbent obtained from agricultural waste rice husk was successfully synthesized through a simple carbon-thermal method. The sorbent was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, N2 sorption analysis, and X-ray photoelectron spectroscopy. The removal efficiency of the sorbent for Cr(VI) was also investigated. Chromium adsorption was fitted by the pseudo-second-order and Langmuir models. The maximum chromium adsorption capacity, Brunauer-Emmett-Teller surface area, and average Barrett-Joyner-Halenda pore size of the magnetic sorbent were 157.7mg·g−1, 134.1m2·g−1, and 4.99 nm, respectively. The saturated magnetization of the novel adsorbent was 77.8 emu·g−1, indicating that the material can facilitate separation and recovery from aqueous systems. The removal mechanisms of Cr(VI) were also discussed. The result illustrates that rice husk-derived magnetic carbonaceous materials are a potential adsorbent for Cr(VI) pollution treatment and provide a suitable method for the effective conversion of biomass waste, which may solve the problem of waste disposal and widen the applications of the materials.

Genetic homogeneity between populations of cotton bollworm from Xinjiang, China

Dongmei Wang,Xianming Yang,Haiqiang Li,Akedan Wuwaishi,Ruifeng Ding,Haobin Li,Hongsheng Pan,Jian Liu,Yao Xu,Yan-Hui Lu 한국응용곤충학회 2018 Journal of Asia-Pacific Entomology Vol.21 No.1

We studied the population structure of cotton bollworm (CBW), Helicoverpa armigera (Hübner) (Lepidoptera:Noctuidae), in Xinjiang, the largest cotton-growing region in China, using a fragment of cytochrome c oxidasesubunit I (COI) gene. Alignments of all 192 COI sequences revealed 28 haplotypes including 23 in southernXinjiang, 5 in eastern Xinjiang and 13 in northern Xinjiang. Negative and significant values of neutrality tests forthe Tajima's D and Fu's FS parameters, combined with the high values of haplotype diversity (Hd), low values ofnucleotide diversity (π) and a high number of low frequency haplotypes indicated a recent demographic expansionof Xinjiang CBW populations. Analysis of molecular variation (AMOVA) indicated low and non-significantgenetic structure, regardless of geographical scale or crop, with most of genetic variation occurringwithin local CBW populations. Pairwise FST analyses also indicated low genetic differentiation. This demographicevent and high gene flow could be responsible for the low genetic structure currently found. CBW populations inXinjiang need to be considered as one panmictic unit in its management, especially for the design of refuges todelay the development of resistance by this migratory pest to transgenic Bt (Bacillus thuringiensis) cotton.

Nonlinear optical properties of indium-doped single-phased TiO2 thin films

Niu Ruifeng,Cui Liqi,Wang Weitian 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.4

Single-phased rutile TiO2 and Ti0.9In0.1O2 thin flms were fabricated using a pulsed laser deposition method. The optical transmission spectra reveal good transparency of the flms in the visible spectral range of 330–900 nm. The absorption edge of the Ti0.9In0.1O2 flm is blue-shifted compared with that of undoped TiO2 flm. The third-order nonlinear optical properties of the flms were investigated using a z-scan method with a pulse laser operating at 532 nm with pulse duration of 55 ps. The results show that the Ti0.9In0.1O2 and TiO2 flms exhibit nonlinear saturable absorption and negative nonlinear refraction properties. The doping of In ions into TiO2 does not change the nonlinear optical absorption signifcantly. However, the nonlinear refractive index of Ti0.9In0.1O2 flm is about two times larger than that of undoped TiO2 flm. The local electronpinned defect-dipoles and widening bandgap in the Ti0.9In0.1O2 flm could be used to explain the observed results.

Kinetics of pentachlorophenol co-metabolism removal by micro-aeration sequencing batch reactor process

Jianhui Wang,Guolong Xie,Xin Qi,Ruifeng Ming,Bin Zhang,Hai Lu 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.6

Four carbon sources (including trehalose, glucose, acetic acid, and yeast extract) were used as the co-metabolicmatrix of pentachlorophenol (PCP). The effect of the carbon sources on the process of acclimatization and degradationof PCP was investigated. The acclimatization rate of carbon sources with different substrates, the activities ofmicrobial enzymes in the co-metabolism process, and the control of co-metabolism reaction conditions were evaluated. The kinetic model of co-metabolic degradation of PCP in micro aerated sequencing batch reactor (SBR) wasestablished based on the Monod equation. The model was applied to fit the operating conditions of the micro aeratedSBR process in this study. The experimental results showed that the type and concentration of metabolic matrix greatlyinfluenced the degradation rate of PCP, and its trehalose, glucose, and acetic acid enhanced the degradation of PCP. Inparticular, the strengthening effect of trehalose was pronounced. When trehalose was used as a co-metabolic carbonsource, the time required for PCP degradation to a predetermined degree was shortened to one-fifth of the original,PCP removal rate exceeded 95%. At the same time, yeast extract inhibited the biodegradation of PCP when it was usedas an additional matrix carbon source. After the co-metabolism carbon source was added to the system, the proliferationrate of the microorganism was increased, and the key enzymes of PCP degradation were induced in the system. When the co-metabolic carbon source concentration was high, it accelerated active enzymes’ induction and maintainedhigh activity; 2,3,5-triphenyltetrazolium chloride-electron transport system (TTC-ETS) activity reached about 7.6mgTF/(gTSS·H), and 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl Tetrazolium chloride-electron transport system(INT-ETS) activity reached 63.5mgINTF/(gTSS·H). When the concentration of co-metabolism carbon source wasextremely high, the co-degradation of toxic organic compounds was inhibited, leading to a decrease in the co-degradationrate. The kinetic model optimized the co-metabolism substrate. The degradation rate of PCP was increased by54.9% by micro-aeration-co-metabolism. The kinetic model was used to fit the microaerobic reaction process of microaeration SBR. The relevant result was in agreement with the experimental result by 97.6%.

Impedance Properties of Phase-Pure Titanium Dioxide Ceramics Sintered at Different Temperatures

Liqi Cui,Ruifeng Niu,Weitian Wang 한국재료학회 2022 한국재료학회지 Vol.32 No.4

In this study, phase-pure titanium dioxide TiO2 ceramics are sintered using standard high-temperature solid-state reaction technique at different temperatures (1,000, 1,100, 1,200, 1,300, 1,400 oC). The effect of sintering temperature on the densification and impedance properties of TiO2 ceramics is investigated. The bulk density and average grain size increase with the increase of sintering temperature. Impedance spectroscopy analysis (complex impedance Z * and complex modulus M *), performed in a broad frequency range from 100 Hz to 10 MHz, indicates that the TiO2 ceramics are dielectrically heterogeneous, consisting of grains and grain boundaries. The complex impedance Z *-plane indicates the resistance of grains of the TiO2 ceramics increases with increasing sintering temperature, while that of grain boundaries develops in the opposing direction. The complex modulus M *-plane shows a grain capacitance that seems to be independent of the sintering temperature, while that of the grain boundaries decreases with increasing sintering temperature. These results suggest that different sintering temperatures have effects on the microstructure, leading to changes in the impedance properties of TiO2 ceramics.

Regional Brain Activity During Rest and Gastric Water Load in Subtypes of Functional Dyspepsia: A Preliminary Brain Functional Magnetic Resonance Imaging Study

Yanwen Chen,Ruifeng Wang,Bo Hou,Feng Feng,Xiucai Fang,Liming Zhu,Xiaohong Sun,Zhifeng Wang,Meiyun Ke 대한소화기 기능성질환∙운동학회 2018 Journal of Neurogastroenterology and Motility (JNM Vol.24 No.2

Background/Aims Functional dyspepsia (FD) remains a great clinical challenge since the FD subtypes, defined by Rome III classification, still have heterogeneous pathogenesis. Previous studies have shown notable differences in visceral sensation processing in the CNS in FD compared to healthy subjects (HS). However, the role of CNS in the pathogenesis of each FD subtype has not been recognized. Methods Twenty-eight FD patients, including 10 epigastric pain syndrome (EPS), 9 postprandial distress syndrome (PDS), and 9 mixed-type, and 10 HS, were enrolled. All subjects underwent a proximal gastric perfusion water load test and the regional brain activities during resting state and water load test were investigated by functional magnetic resonance imaging. Results For regional brain activities during the resting state and water load test, each FD subtype was significantly different from HS (P < 0.05). Focusing on EPS and PDS, the regional brain activities of EPS were stronger than PDS in the left paracentral lobule, right inferior frontal gyrus pars opercularis, postcentral gyrus, precuneus, insula, parahippocampal gyrus, caudate nucleus, and bilateral cingulate cortices at the resting state (P < 0.05), and stronger than PDS in the left inferior temporal and fusiform gyri during the water load test (P < 0.05). Conclusions Compared to HS, FD subtypes had different regional brain activities at rest and during water load test, whereby the differences displayed distinct manifestations for each subtype. Compared to PDS, EPS presented more significant differences from HS at rest, suggesting that the abnormality of central visceral pain processing could be one of the main pathogenesis mechanisms for EPS.

Effects of sintering temperature on the dielectric and impedance properties of phase-pure titanium dioxide ceramics

Liqi Cui, Ruifeng Niu,Weitian Wang 한양대학교 세라믹연구소 2022 Journal of Ceramic Processing Research Vol.23 No.1

In this study, phase-pure titanium dioxide TiO2 ceramics were sintered at different temperatures (1,000, 1,100, 1,200, 1,300,1,400 oC). The effects of sintering temperature on the compaction, dielectric and impedance properties were investigated. Frequency and temperature dependencies of dielectric permittivity and dielectric loss were revealed by using dielectricmeasurements. When the TiO2 ceramics sintered at 1,400 oC, it exhibits the larger dielectric constant and the smaller dielectricloss as a result of increased density and decreased porosity. The analysis of complex impedance in the frequency range 100Hz-10 MHz indicated that the TiO2 ceramics were dielectrically combinations of bulk grains and grain boundaries. Theseresults suggest that the sintering temperatures have effects on the microstructure, leading to the variations in dielectric andimpedance properties of TiO2 ceramics.