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Mg-doping towards enhancing the composition-phase-structural stability of Li-La-zirconate based cubic garnet upon exposure to air
摘要： Mg, as a new dopant, has been found to stabilize the desired cubic garnet structure (Ia3d) of Li-La-zirconate (LLZO) and lead to Li-ion conductivities similar to those obtained with the same level of Al-doping. More importantly, Mg-doping, as opposed to Al-doping, suppresses the deleterious reactions with the atmospheric moisture/CO2, leading to stability in the composition-phase-structure upon exposure to air. Accordingly, when exposed to air, even though Al-doped LLZO pellets get spontaneously fractured/disintegrated, accompanied by reduction in ionic conductivity by ~3 orders of magnitude, Mg-doped LLZO shows no sign of cracking and almost retains the ionic conductivity measured prior to exposure.
关键词： Ionic conductivity,Mg-doping,Composition-phase-structural stability,Lithium garnet,Solid electrolyte
更新于2025-09-04 15:30:14
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Three-dimensional anisotropic thermal conductivity tensor of single crystalline β-Ga <sub/>2</sub> O <sub/>3</sub>
摘要： β-Ga2O3 has attracted considerable interest in recent years for high power electronics, where the thermal properties of β-Ga2O3 play a critical role. The thermal conductivity of β-Ga2O3 is expected to be three-dimensionally (3D) anisotropic due to the monoclinic lattice structure. In this work, the 3D anisotropic thermal conductivity tensor of a (010)-oriented β-Ga2O3 single crystal was measured using a recently developed elliptical-beam time-domain thermoreflectance method. Thermal conductivity along any direction in the (010) plane as well as the one perpendicular to the (010) plane can be directly measured, from which the 3D directional distribution of the thermal conductivity can be derived. Our measured results suggest that at room temperature, the highest in-plane thermal conductivity is along a direction between [001] and [102], with a value of 13.3 ± 1.8 W m?1 K?1, and the lowest in-plane thermal conductivity is close to the [100] direction, with a value of 9.5 ± 1.8 W m?1 K?1. The through-plane thermal conductivity, which is along the [010] direction, has the highest value of 22.5 ± 2.5 W m?1 K?1 among all the directions. The temperature-dependent thermal conductivity of β-Ga2O3 was also measured and compared with a theoretical model calculation to understand the temperature dependence and the role of impurity scattering.
关键词： monoclinic lattice,β-Ga2O3,anisotropic,time-domain thermoreflectance,thermal conductivity
更新于2025-09-04 15:30:14
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Microwave cavity perturbation of nitrogen doped nano-crystalline diamond films
摘要： Non-contact and non-destructive electrical conductivity measurements of nitrogen doped nano-crystalline diamond films have been demonstrated using a microwave cavity perturbation system. The conductivity of the films was controlled by simply varying the CH4 gas concentration during microwave plasma assisted chemical vapour deposition, thereby promoting the formation of sp2 carbon at the grain boundaries. The presence of sp2 carbon is verified through Raman spectroscopy, x-ray photoelectron spectroscopy and electron energy loss spectroscopy, while scanning electron microscopy confirms an increasing surface area for sp2 to form. The microwave cavity perturbation results show that the measured cavity quality factor varies with CH4 concentration. The extraction of conductivity is achieved through a depolarisation model, which must be considered when the sample is smaller than the cavity and through both electric and magnetic field perturbations. The microwave measurements are comparable to contacting and damaging measurements when the film conductivity is greater than the substrate, thus demonstrating an invaluable method for determining conductivity without the need for depositing any electrodes on the film.
关键词： non-contact,microwave dielectric spectroscopy,nano-crystalline diamond,electrical conductivity
更新于2025-09-04 15:30:14
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Influence of Pb on structure, optical and electrical properties of Zn1-XPbXS semiconductor compounds at low temperatures
摘要： Zn1-XPbXS (x = 0–0.4 in steps of 0.1) ternary semiconductor samples have been prepared by co-precipitation method. The structural, optical and electrical studies have been carried out on all these samples to understand the influence of Lead on these properties. X-ray diffractograms showed that all Zn1-XPbXS samples have poly-crystalline nature with Hexagonal phase. The room temperature optical absorption studies revealed that energy gap decreases with increase of Pb in Zn1-XPbXS compounds. The temperature-dependent conductivity, measured in the range 300–4 K, led to understand that the conduction mechanisms at 60 K and 30 K are different. The activation energies evaluated at low (300–60 K) and very low temperature (60–30 K) regions are 38.03–32.58 meV and17.99–13.56 meV respectively. Activation energy and conductivity of Zn1-XPbXS samples increase with the increase of Pb. The samples exhibited low freezing temperature points indicating the possibility of their use in low temperature device applications.
关键词： Ternary semiconductor,Energy gap,Activation energy,Electrical conductivity
更新于2025-09-04 15:30:14
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Deep level acceptors of Zn-Mg divalent ions dopants in β-Ga2O3 for the difficulty to p-type conductivity
摘要： β-Ga2O3 exhibits huge potential applications in next-generation power electronics with its wide band gap, large breakdown field and high Baligas’s figure of merit. The achievement of p-type conductive β-Ga2O3 faces hugely challenge due to the self-compensating process, while that is critically important to further extend its utility and applications. Although the acceptor deep levels of divalent ions dopants can explain the difficulty of p-type Ga2O3 theoretically, while the experimental evidence is lacked. Herein, Zn and Zn-Mg co-doped β-Ga2O3 thin films were prepared to investigate the acceptor levels of ZnGa and MgGa. The XPS results indicate that both Zn and Mg exhibit divalent ions when they replaced trivalent Ga ion. The doping concentration and band gap can modulate by solely changing the numbers of Zn and Mg pieces during the deposition process. The levels of ZnGa and MgGa are located at 0.79 eV and 1.00 eV respectively speculated by photoluminescence, such deep acceptor transition levels proved that it is difficult to obtain highly conductive p-type Ga2O3 by doping with divalent ions of Zn and Mg.
关键词： acceptor levels,p-type conductivity,photoluminescence,Zn-Mg doping,β-Ga2O3
更新于2025-09-04 15:30:14
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Improvement of Electrical Conductivity and Chemical Durability in Fe <sub/>2</sub> O <sub/>3</sub> Doped V <sub/>2</sub> O <sub/>5</sub> –B <sub/>2</sub> O <sub/>3</sub> –P <sub/>2</sub> O <sub/>5</sub> Glasses
摘要： In this study, we veri?ed the relationship among the electrical conductivity, chemical durability, and structure of conductive vanadate glass in which Fe2+–Fe3+ and V4+–V5+ systems simultaneously coexist. We prepared samples of iron vanadium borophosphate glass with various compositions given by 78V2O5–15P2O5–7B2O3–xFe2O3 (1, 5, 7.5 and 10 mol%) and analyzed the electrical conductivity, chemical durability, FTIR spectra, thermal properties, density, and molar volume. The results indicated that the addition of Fe2O3 improved the electrical conductivity, chemical durability, and thermal properties. The following conclusions could be drawn: Fe2+–O–P bonds or Fe3+–O–P bonds were generated in the glass structure, and Fe3+ and Fe2+ ions were located at tetrahedral and octahedral sites. Furthermore, V O bonds were expected to be replaced with Fe–O–V and P–O–V bonds, which are stronger than double bonds, so that the complete glass structure was strong. The structural reinforcement of the glasses was additionally con?rmed based on thermal and chemical properties and electrical conductivity.
关键词： Water Resistance,Transition Metal Oxide,Vanadate Glass,Conductivity,Glass Structure
更新于2025-09-04 15:30:14
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Synthesis of novel form-stable composite phase change materials with modified graphene aerogel for solar energy conversion and storage
摘要： In this study, novel kinds of form-stable composite phase change materials (FS-CPCM) were prepared by the vacuum impregnation method. In the FS-CPCM, lauric acid (LA) was the PCM, and LA was grafted on the surface of graphene aerogel (GA) by an esteri?cation reaction and reduction process to prepare supporting material and increase the thermal conductivity of the FS-CPCMs. The microstructure, thermal storage properties, thermal conductivity and light-to-heat conversion of the FS-CPCMs were investigated. Scanning electron microscopy and Fourier transform infrared spectroscopy were used to demonstrate that the LA was encapsulated e?ectively in the porous structure of the LA-GA, and the LA/LA-GA FS-CPCMs were prepared successfully. X–ray di?ractometer results con?rmed that the crystallization of the LA/LA-GA FS-CPCM was better than that of LA/GA FS-CPCM. Thermal conductivity analyses indicated that the thermal conductivities of the LA/LA-GA-1 FS-CPCMs increased 352.1% and 32.6% compared with the conductivities of LA and LA/GA FS-CPCM, respectively. Di?erential scanning calorimetry results con?rmed that the LA/LA-GA-1 FS-CPCM possess good phase change behavior, low undercooling and excellent thermal cycling stability. The melting enthalpy and freezing enthalpy could reach 207.3 J/g and 205.8 J/g, respectively, and the LA/LA-GA FS-CPCM exhibited good thermal reliability and stability. Furthermore, the LA/LA-GA FS-CPCM had excellent photon absorption and the highest e?ciency in terms of light-to-heat conversion of 80.6%. Such good performances demonstrate the LA/LA-GA FS-CPCM's potential for use in solar energy storage systems.
关键词： Phase change materials,Thermal conductivity,Graphene aerogel,Solar energy conversion
更新于2025-09-04 15:30:14
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Electrolyte Factors Influencing Separated Pore Growth of Anodic TiO2 Nanotube Arrays
摘要： This work presents an investigation of electrolyte properties in relation to the growth of TiO2 nanotube array films, particularly concerning the measurement of conductivity in the diethylene glycol-hydrofluoric-water electrolyte system. The work aims to elucidate the behavior of ions in the anodized electrolytes with a better insight into the relation between molar conductivity and concentration of the additives. Differing solvation of the fluoride ion in various composition of water in the DEG-H2O mixture is attributed to the major factor determining the capability of proton transfer, controlling the ionic mobilities and the molar conductivities. Applying the feature of the two-factorial experiment has demonstrated a clear interaction of electrolyte parameters and titanium concentration dissolving into the electrolyte, which is believed to be a combination effect on pore widening and separating of nanotubes. A proposed schematic drawing has been demonstrated, summarizing how the nanotube arrays are constructed as a consequence of varying electrolyte type and composition.
关键词： electrochemical anodization,tube separation,TiO2 nanotube arrays,electrolyte conductivity
更新于2025-09-04 15:30:14
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Structural Aspects at Phase Transitions in Ferroelectric Copolymers of Vinylidenefluoride and Tetrafluoroethylene
摘要： low-voltage Permittivity and conductivity temperature dependences of a ferroelectric copolymer of vinylidenefluoride VDF with tetrafluoroethylene TFE in the ferroelectric to paraelectric phase transition range were investigated. The as received films obtained by crystallization from a solution had the metastable structure shown in particular in coexistence of ferroelectric and paraelectric phases below a Curie point. Temperature dependences of electrical characteristics in the first and second cycles of heating differ. Low glass transition (?40 oC) facilitate intensive micro-Brownian chains mobility in the amorphous phase at ambient temperatures and above. As per the x-ray and spectroscopic data, the first heating cycle will result in a recrystallization process for molecular structure improvement. Asymmetry of temperature dependence of a dielectric susceptibility in a vicinity of “order-disorder” phase change is found out. For the first time paid attention to the fact that for crystalline polymer ferroelectrics interpretation of the parameters of the temperature dependences of the dielectric susceptibility in the cycle of heating near the phase transition point should take into account the possibility of the premelt processes. First the method of IR spectroscopy shows that the melting of ordered structures, emerging secondary crystallization is accompanied by a change of the basic parameters (frequency position, the integral intensity and half-width) component of the doublet of valence vibrations of С-Н groups. Such structural changes lead to the emergence of “anomalies” on the temperature dependences of conductivity.
关键词： conductivity,IR-spectroscopy,phase transitions,Ferroelectric polymers,structure
更新于2025-09-04 15:30:14
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Electron and phonon transport properties of layered Bi <sub/>2</sub> O <sub/>2</sub> Se and Bi <sub/>2</sub> O <sub/>2</sub> Te from first-principles calculations
摘要： Recent experiments indicated that both layered Bi2O2Se and Bi2O2Te are promising thermoelectric materials with low thermal conductivities. However, theoretical study on the thermoelectric properties, especially the phonon transport properties, is rare. In order to understand the thermoelectric transport mechanism, we here investigate the electron and phonon transport properties by using the first-principles calculations combined with the Boltzmann transport theory. Our results indicate that both Bi2O2Se and Bi2O2Te are semiconductors with indirect energy gaps of 0.87 eV and 0.21 eV within spin–orbit coupling, respectively. Large Seebeck coefficient and power factor are found in the p-type than the n-type for both compounds. Low lattice thermal conductivities at room temperature are obtained, 1.14 W m?1 K?1 for Bi2O2Se and 0.58 W m?1 K?1 for Bi2O2Te, which are close to the experimental values. It is found that the low-frequency optical phonon branches with higher group velocity and longer lifetime also make a main contribution to the lattice thermal conductivity. Interestingly, the lattice thermal conductivity exhibits obvious anisotropy especially for Bi2O2Te. These results are helpful for the understanding and optimization of thermoelectric performance of layered Bi2O2Se and Bi2O2Te.
关键词： thermoelectric,Bi2O2Se,lattice thermal conductivity,Bi2O2Te,first-principles
更新于2025-09-04 15:30:14