In-plane Dielectric Properties of Epitaxial Orthorhombic HoMnO3 Films Grown on LaAlO3 Substrates

Weitian Wang,Ping Gao,Wei Zhang,Yuming Sun 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.9

Orthorhombic HoMnO₃ thin films were grown epitaxially on LaAlO₃ (001) substrates by using apulsed laser deposition technique. The films showed perfectly orthorhombic crystallization and werewell-aligned with the substrates. The in-plane dielectric constant and the dielectric loss of HoMnO₃films were measured as functions of temperature (80 ~ 300 K) and frequency (120 ~ 100 kHz) byusing interdigital surface electrodes. Two thermally-activated dielectric relaxations were found, andthe respective peaks shifted to higher temperatures as the measuring frequency was increased. Thein-plane dielectric properties of epitaxial orthorhombic HoMnO₃ films were considered to have auniversal dielectric response behavior, and the dipoar effects and the hopping conductivity inducedby the charge carriers were used to explain the results. The dielectric properties at low temperatures,which showed the multiferroicity, of the orthorhombic HoMnO₃ films are discussed.

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.

Optical properties of InN rods on sapphire grown by metal–organic chemical vapor deposition

Sun, Yuanping,Cho, Yong-Hoon,Dai, Zhenhong,Wang, Weitian,Wang, Hui,Wang, Lili,Zhang, Shuming,Yang, Hui Elsevier 2010 Physica E, Low-dimensional systems & nanostructure Vol.43 No.1

<P><B>Abstract</B></P><P>The InN rods were grown by metal–organic chemical vapor deposition with a density of 1.4×10<SUP>9</SUP>cm<SUP>−2</SUP>. Optical properties of InN rods have been systematically investigated by means of temperature dependent photoluminescence (PL) and power dependent PL. Four peaks appear in the PL spectra and the origination was analyzed. The lowest energy peak P1 (0.665eV) is attributed to transitions of conduction band electrons to the photo-holes captured by deep acceptor; P2 (0.717eV) is the direct band-to-band transition peak of InN; main peak P3 (0.759eV) results from the recombination of degenerate electrons with photo-holes near the top of the valence band (Burstein–Moss effects); the high energy shoulder P4 (0.787eV) was by the co-effect of quantum confinement and the Burstein–Moss effects due to the small size distribution of InN wetting layers.</P>

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.

Linear and Nonlinear Optical Properties of Vanadium Pentoxide Films Prepared by Pulsed-Laser Deposition

Cui, Liqi,Wang, Ruiteng,Wang, Weitian Materials Research Society of Korea 2021 한국재료학회지 Vol.31 No.7

Well-crystallized vanadium pentoxide V₂O₅ thin films are fabricated on MgO single crystal substrates by using pulsed-laser deposition technique. The linear optical transmission spectra are measured and found to be in a wavelength range from 300 to 800 nm; the data are used to determine the linear refractive index of the V₂O₅ films. The value of linear refractive index decreases with increasing wavelength, and the relationship can be well explained by Wemple's theory. The third-order nonlinear optical properties of the films are determined by a single beam z-scan method at a wavelength of 532 nm. The results show that the prepared V₂O₅ films exhibit a fast third-order nonlinear optical response with nonlinear absorption coefficient and nonlinear refractive index of 2.13 × 10^-10 m/W and 2.07 × 10^-15 cm²/kW, respectively. The real and imaginary parts of the nonlinear susceptibility are determined to be 3.03 × 10^-11 esu and 1.12 × 10^-11 esu, respectively. The enhancement of the nonlinear optical properties is discussed.

Optical Absorption Properties of Dielectric Composite Films Doped with Metal Nanoparticles

Huiwen Lu,Weitian Wang 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.12

Composite thin films formed by using nanometer-sized metal particles embedded in dielectric matrices were fabricated by using a pulsed laser deposition technique to co-deposit the metal and the ceramic targets. The optical absorption properties were measured at wavelength from 350 to 800 nm, and the absorption peak due to the surface plasmon resonance of the metal particles was found. The effects of different metal particles (Au, Ag, Fe, Co) and different embedding matrices (SrTiO3, Al2O3, and TiO2) on the optical absorption properties of dielectric composite films are discussed. Strong absorption peaks can be found in composite films doped with noble-metal particles while the composites doped with most transition-metal particles show ordinary absorption patterns. The dielectric properties of the metal particles and the refractive indices of the embedding matrices were responsible for the observed results.

Optical properties of transition-metal oxide thin films deposited using a pulsed laser

Cui Liqi,Wang Ruiteng,Wang Weitian 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.2

Transition-metal oxide thin films of V2O5, ZrO2, and CeO2 were fabricated on MgO single-crystal substrates using a pulsedlaser deposition technique. The linear optical transmission spectra were measured at room temperature, and the data showing a fringe pattern in the transparent spectral region were used to determine the linear refractive indices of the films. The values of the linear refractive indices decrease with increasing wavelength, and the relationship could be well explained using Wemple’s theory. The third-order nonlinear optical properties of the films were determined using a single-beam z-scan method at a wavelength of 532 nm. The results showed that the prepared V2O5 film exhibited a fast third-order nonlinear optical response, with the nonlinear absorption coefficient and the nonlinear refractive index being 3.97 × 10–10 m/W and 4.55 × 10–17 m2/ W, respectively, which are larger than those for the ZrO2 and the CeO2 films. The metal–oxygen bond lengths based on the bond-orbital theory could be used to explain these results.

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.

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.