Effect Of Li Doping Research Articles

Effects of Li doping on microstructural and electrical properties of ZnO–MgO–Al2O3 linear resistance ceramics

Effects of Li doping on microstructural and electrical properties of ZnO–MgO–Al₂O₃ linear resistance ceramics

Fabrication of Fast-response Ultraviolet Light Sensors with LZO Thin Films using Sol-gel Spin-coating Method

The Li-doped ZnO (LZO) thin films with various Li concentrations (0, 1, 3, 5, 7, and 9 at.%) were deposited on quartz substrates by sol-gel spin-coating method. The effects of Li doping on the structural and optical properties of the thin films were investigated. Undoped ZnO thin film and LZO thin films had three different diffraction peaks at 31.5 °, 34.2 °, and 36.0 °corresponding to the ZnO (100), (002), and (101) planes, respectively. The c-axis orientation of the LZO thin films increased with increasing Li doping concentration, owing to the high diffusivity of the Li dopant. A broad red emission was observed by photoluminescence of the undoped ZnO thin film, whereas LZO thin films had broad green emissions. The transmittance and optical band gap blue-shifted with increasing Li doping concentration. In terms of photoresponse, all LZO thin films had greater rise and decay rates than the undoped ZnO thin film and the photosensitivity increased with increasing Li doping concentration.

Effects of Li doping on the structural and electrical properties of solution-processed ZnO films for high-performance thin-film transistors

We report the structural and electrical properties of Li-doped ZnO (LZO) films, which are spin-coated via a simple solution process using Zn and Li precursor solutions. The Li doping improves the crystallinity of the ZnO films, and the LZO films exhibit a relatively dense and smooth surface morphology compared to that of the undoped ZnO films. Back-gated LZO thin-film transistors (TFTs) are fabricated onto a heavily p-doped Si substrate with a SiO2 gate dielectric, and operated in enhancement mode. In the case of the LZO TFT with a Li doping concentration of 0.50 mol%, the highest field-effect mobility of 5.18 cm2 V−1 s−1 is obtained; the on/off current ratio and subthreshold swing are 107 and 1.2 V dec−1, respectively. These results demonstrate that Li doping can effectively modulate the structural and electrical properties of ZnO-based films, facilitating the fabrication of LZO TFTs with enhanced performance.

Optical and biological properties of plasma-treated Neurospora crassa spores as studied by absorption, circular dichroism, and Raman spectroscopy

Zn1−xLixO films were spin-coated on platinum substrates by using sol-gel method. The XRD pattern demonstrated that the Li doped ZnO films exhibits the hexagonal wurtzite structure. And, the 18.5 ◦ peak was found at dopant content from 0.15 to 0.2, which could be attributed to the (003) plane of Li2PtO3. The effect of Li doping and emission in relation to defects is investigated using CL. Zn1−xLixO films show two characteristic emission peaks centered at near 383 nm and near 530 nm, respectively. The peak position of the UV emission is not changed when the Li content is increased from 0.0 to 0.2. The green emission peak increase abruptly at 0.1 Li content, however, decreases gradually with increasing Li content. The dielectric constant increases with increasing Li content up to 0.15, and decreases when lithium is added at 0.2. The ferroelectric polarization was measured using a polarization-electric field hysteresis loop. At x = 0.15, the measured values of spontaneous polarization and coercive field were 0.25 μC/cm2 and 1.6 kV/cm at room temperature, respectively.

Effects of Li doping and point defect on the magnetism of ZnO

The magnetism sources and magnetic mechanism of Li doping and point defect, which coexist in the presence of hexagonal wurtzite ZnO, are controversial. To solve these problems, the effects of Li doping and point defect on the magnetism of ZnO were studied using geometry optimization and energy calculation based on the first-principle generalized gradient approximation + U (GGA + U) method of density functional theory. Results showed that the coexistence of Li doping and Zn vacancy can achieve ferromagnetic long-range order, and the Curie temperature of the doping system can achieve room temperature. In addition, results showed that magnetic moments are significantly different when the structures of the systems are also different with the same doping amount and doping method, which are advantageous for the enhancement of the magnetic properties of dilute magnetic semiconductors. The magnetism source of Zn14LiO16 is the hybrid coupling electron exchange effect between O-2p and Zn-3d orbits. With the coexistence of Li replacing Zn and Zn vacancy, the closest relative distance between doping and vacancy leads to the lowest formation energy and highest stability. In the condition of the highest stability of the ground state, all the doping systems of Li replacing Zn and O vacancy, doping system of interstitial Li and Zn vacancy, and doping system with the coexistence of Li replacing Zn, interstitial Li, and Zn vacancy are non-magnetic, which are considered worthless in the design and preparation of diluted magnetic semiconductors (DMSs).

Effect of Li doping on the electric and pyroelectric properties of ZnO thin films

Un-doped ZnO (UDZO) and Li-doped ZnO (LZO) polycrystalline thin films were grown on platinized silicon by pulsed laser deposition (PLD). The electrical properties were investigated on as-grown and annealed UDZO and LZO films with capacitor configuration, using top and bottom platinum electrodes. In the case of the as-grown films it was found that the introduction of Li increases the resistivity of ZnO and induces butterfly shape in the C-V characteristic, suggesting ferroelectric-like behavior in LZO films. The properties of LZO samples does not significantly changes after thermal annealing while the properties of UDZO samples show significant changes upon annealing, manifested in a butterfly shape of the C-V characteristic and resistive-like switching. However, the butterfly shape disappears if long delay time is used in the C-V measurement, the characteristic remaining non-linear. Pyroelectric signal could be measured only on annealed films. Comparing the UDZO results with those obtained in the case of Li:ZnO, it was found that the pyroelectric properties are considerably enhanced by Li doping, leading to pyroelectric signal with about one order of magnitude larger at low modulation frequencies than for un-doped samples. Although the results of this study hint towards a ferroelectric-like behavior of Li doped ZnO, the presence of real ferroelectricity in this material remains controversial.

Effect of Li-doping on low temperature solution-processed indium–zinc oxide thin film transistors

Lithium (Li)-doped indium zinc oxide (IZO) thin film transistors (TFTs) were fabricated on solution-processed zirconium oxide gate dielectrics using a low temperature all solution process. Li-doping in IZO thin films led to higher crystallinity, even at process temperature lower than 300°C, and to the formation of favorable oxidation states of metal ions. The results were confirmed by electrical property analysis of the Li-doped IZO TFTs. For Li content varied from 0 to 16.6 at.%, the highest field-effect mobility, on/off current ratio, subthreshold slope and stress bias stability were obtained for Li-doping concentration of 9.0mol%.

Effects of Li doping on structural, electronic, optical and magnetic properties of Fe 0.04 Zn 0.96 O nanocrystalline samples

Abstract Sol-gel synthesized nanocrystalline samples of Li x Fe 0.04 Zn 0.96−x O (x = 0.0, 0.02, 0.04 and 0.06) have been investigated through X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), UV–visible absorption spectroscopy and magnetic measurements. First three samples, i.e., x = 0.0, 0.02 and 0.04, have been found to possess an impurity phase of ZnFe 2 O 4 . As determined from the Rietveld analysis, the presence of ZnFe 2 O 4 phase has decreased on Li doping and for x = 0.06, it is negligibly small. XANES analysis shows that the majority of Fe ions is in Fe 3+ state. From the UV–visible spectroscopy, the energy band gap (E g ) of pure ZnO has been estimated to be 3.064 eV, whereas on Fe doping E g has increased. No significant change in E g due to Li doping has been observed. Magnetization measurements have revealed that the samples containing ZnFe 2 O 4 (x = 0.0, 0.02 and 0.04) phase exhibit strong ferromagnetic spin-glass behaviour at low temperature and a weak ferromagnetic ordering at the room temperature. However, the sample with x = 0.06 does not show any significant ferromagnetic ordering in the temperature range of 2–300 K. The observed magnetic ordering and spin-glass behaviour in first three samples have been attributed to the impurity phase of ZnFe 2 O 4 .

Effect of Li doping on the superconducting properties of single domain GdBCO bulks fabricated by the top-seeded infiltration and growth process

Single domain GdBCO bulk superconductors have been fabricated by the top-seeded infiltration and growth process (Gd+011 TSIG) with solid phase compositions of (1-x)(Gd2O3+1.2BaCuO2)+xLi2CO3, (x=0, 0.04, 0.08, 0.10, 0.12, 0.16wt%). The effect of Li2CO3 doping on the growth morphology, microstructure, levitation force, trapped field and critical temperature (Tc) of single domain GdBCO bulks have also been investigated based on these samples. The results show that the single-domain GdBCO bulks can be fabricated when x is in the range of 0–0.16wt%. The size and distribution of Gd211 particles are not influenced by the Li2CO3 doping in the samples. The Tc of the samples decrease from 92.5K (x=0wt%) to 89.5K (x=0.16wt%) when x increases. The decreasing trend of Tc was caused by the substitution of Li+ on Cu2+ site in the GdBCO crystal. Both of the levitation forces and trapped fields of the samples increase first and then decrease with the increase of x; both of the largest levitation force of 38.5N（77K，0.5T） and the largest trapped field of 0.31T（77K，0.5T） are obtained in the sample when x=0.10wt%. These results show that appropriate Li doping is an effective way to enhance the flux pinning force and the other physical properties of GdBCO bulk superconductors fabricated by the Gd+011 TSIG method.

Effect of Li doping on sintering characteristics and microstructural behavior of yttria-stabilized zirconia

The sintering behavior of Li-doped yttria-stabilized zirconia (YSZ) was investigated. Li doping in YSZ reduced the densification temperature and enhanced grain growth, as a result of the formation of a lithium-zirconate-related eutectic liquid during sintering. For 5at% Li doping, the sample developed a duplex microstructure consisting of small grains with second phase particles in the inner region and large grains with pores in the surface region. The second phase of Li2ZrO3 near the surface of the sample decomposed into Li2O and ZrO2, followed by the evaporation of Li2O during sintering, leaving behind large pores in the microstructure.

One-step synthesis of Li-doped NiO as high-performance anode material for lithium ion batteries

The poor electronic conductivity and huge volume expansion of NiO are the vital barriers when used as anode for lithium ion batteries. In order to solve above issues, Li-doped NiO are prepared by a facile one-step ultrasonic spray pyrolysis method. The effects of Li doping on the morphology, structure and chemical composition of the Li-doped NiO powders are extensively studied. When used as lithium ion batteries anode, it is demonstrated that the doping of Li has significant positive effect on improving the electrochemical performance. After 100 cycles at 400mAg−1, The Li-doped NiO samples deliver a discharge capacity of 907mAhg−1, much more than that of un-doped sample (736mAhg−1). The improved electrochemical performances can be ascribed to the improved p-type conductivity and lower impedance, which are confirmed by Rietveld refinement, X-ray photoelectron spectroscopy and electron impedance spectroscopy.

Photovoltaic properties of LixCo3−xO4/TiO2 heterojunction solar cells with high open-circuit voltage

All-oxide solar cells are presently attracting extensive research interest due to their excellent stability, low-cost and non-toxicity. However, the band gap of metal oxides is lack of effective optimization and results in poor photovoltaic performance, thus hindering their practical applications. In this work, Co3O4 was investigated for application as a photo-absorber in all-oxide solar cells, and its band gap was optimized by introducing Li dopant into the spinel structure. LixCo3−xO4 nanoparticles, prepared via the hydrothermal method, were homogenously coated onto TiO2 mesoporous films, which were then used to fabricate planar heterojunction TiO2/LixCo3−xO4 solar cells (SCs). The effects of Li-doping on the heterojunction solar cell performance were further investigated. The findings revealed that the incorporation of Li ions into Co3O4 led to a significant enhancement in short-circuit current density (Jsc). Remarkably, a high open-circuit voltage (Voc) of 0.70V was also achieved. Besides, reasons for the enhanced cell performance are the narrower band gap, reduced photogenerated carrier recombination and the more favorable energy band structure as compared with SCs assembled from pure Co3O4.

The effect of Li doping on the nonlinear optical properties of [2.2]paracyclophane.

The similar molecules [2.2]paracyclophane (22PCP) and 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane (8F22PCP) have both generated considerable synthetic interest since they were first prepared. In this work, the nonlinear optical properties of 22PCP, 8F22PCP, and the related Li-doped systems 22PCP-Li and 8F22PCP-Li (which have a Li atom above 22PCP and 8F22PCP, respectively) were investigated. An analysis of natural bond orbital charges showed that there is greater charge transfer from the Li atom to the benzene rings in 8F22PCP-Li than in 22PCP-Li. The variation in the calculated nucleus independent chemical shift (NICS) value as a function of the distance from the lower benzene ring towards the upper benzene ring was found to be W-shaped for both 22PCP and 22PCP-Li. Moreover, whereas all of the NICS values of 22PCP and 22PCP-Li were markedly negative, all of the NICS values of 8F22PCP and 8F22PCP-Li were either positive or only moderately negative. Calculations of the electro-optical properties of these systems showed that the first hyperpolarizability of 22PCP-Li was noticeably larger than that of 8F22PCP-Li. According to the two-level model, the larger first hyperpolarizability of 22PCP-Li is due to its smaller transition energy.

First-principles calculation of the effects of Li-doping on the structure and piezoelectricity of (K0.5Na0.5)NbO3 lead-free ceramics.

The crystal structures of the lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 and (K0.5Na0.5)0.94Li0.06NbO3 prepared by a solid-state method were investigated using first-principles calculations. The calculated values of piezoelectricity were in good agreement with the experimental data. We found that the primary contribution to piezoelectricity in this material comes from the hybridization of the O 2p and Nb 4d orbitals, which causes a change in the Nb-O bond length and the distortion of the Nb-O octahedral structure. Analysis of the band structure and the total density of states revealed that Li-doped (K0.5Na0.5)NbO3 enhances hybridization of the O 2p and Nb 4d orbitals. This hybridization enhancement further reduces the Nb-O1 bond length and enhances the distortion of the Nb-O octahedron along the [001] direction, which may be the main reason for the improvement of the piezoelectric properties. In addition, the piezoelectric coefficients are calculated here, which show the same trend as the experimental results.

Effect of Li-doping on polar-nanoregions in K(Ta1−xNbx)O3 single crystals

The anomalous changes of the elastic properties in the vicinity of the Curie temperature, TC = 304 K, of a 5%Li-doped KTa1−xNbxO3 (KTN) single crystal were investigated by micro-Brillouin scattering. By the Li-doping, the temperature region of the elastic anomaly was extended in comparison with a non-doped KTN crystal. This fact indicates that the Li-doping enhances the growth of polar nanoregions (PNRs), while the remarkable elastic anomaly just above TC is suppressed. The growth of PNRs was also evident from the change in the behavior of the central peak (CP) in comparison with the non-doped KTN. The broadening of the elastic anomaly can be the evidence of the enhanced diffusive nature of the ferroelectric phase transition, which is induced by Li ions.

Lithium-doped PEO—a prospective solid electrolyte with high ionic conductivity, developed using n-Butyllithium in hexane as dopant

The present work is an effort to study the effects of Li doping on the structural and transport properties of the solid polymer electrolyte, poly-ethelene oxide (PEO) (molecular weight, 200,000). Li-doped PEO was synthesized by treating PEO with n-Butyllithium in hexane for different doping concentrations. It is seen that the crystallinity of the doped PEO decreases on increasing the Li doping concentration and XRD and FTIR studies support this observation. FESEM images give better details of surface morphology of doped PEO samples. The TGA curves of PEO and Li-doped PEO samples reveal the weight loss region, and it is observed that the weight loss process of the solid polymer electrolyte is gradual rather than abrupt, contrary to the case of liquid electrolytes. The purity and the electrochemical stability of the samples were established by cyclic voltammetry studies. Impedance measurements were carried out to estimate the ionic conductivity of Li-doped PEO samples. The present value of ionic conductivity observed at room temperature in Li-doped PEO is about five orders higher than that of pure PEO and is quite close to that of liquid electrolytes. It is inferred that, ionic conductivity of the sample is increasing on increasing the Li doping concentration due to enhanced charge carrier density and flexibility of the doped sample structure. The ionic mobility and ionic transport are significantly improved by the less crystallinity and higher flexibility of the Li-doped PEO samples which in turn are responsible for the enhanced ionic conductivity observed.

Modulating the charge transfer of D-S-A molecules: structures and NLO properties.

Very recently, the investigation of an Li atom doped effect on the "through-space" electronic interaction (S) of a donor-S-acceptor (D-S-A, 1) shows that the Li-doping effect can modulate the first hyperpolarizability of 1 ( Dyes Pigm. 2014 , 106 , 7 - 13 ). Can we further enhance the first hyperpolarizability (βtot) of 1 by modulating the charge transfer of D-S-A molecules? The present work indicates that the βtot value can be successfully modulated by replacing the sp(2)-hybridized CH═CH moiety connected with substituted para-cyclophane (PCP). On the other hand, the NO2 contributes more than NH2 to the βtot value. The results of time-dependent density functional theory (TD-DFT) provide a good explanation for the variation in the βtot value. Interestingly, the βtot value of 3 (4.09 × 10(3) au) is larger than 1.52 × 10(3) au of 4, while the difference between the dipole moments (Δμ) of the ground state and the crucial excited state of 3 (2.93 D) is smaller than that of 4 (7.79 D). Further, the charge-transfer excitation length (D(CT)) of 3 (1.41 Å) is smaller than that of 4 (2.89 Å). Therefore, D(CT) is the major factor in determining the Δμ value.

Li doping effect on the photoluminescence behaviors of KSrPO4:Dy3+ phosphors for WLED light

A novel warm-white phosphor KSrPO4 co-doped with Dy3+ and Li+ ions was prepared by solid state reaction. A strategy of Li+ doping was used with the aim of enhancing the luminescence of 475nm and 570nm emission bands under NUV excitation. Compared to lithium-free KSrPO4:Dy3+, the intensities of the 570nm emission peaks were increased by 4.32 times and 2.84 times excited by 351nm and 388nm with 6mol% Li+ ions co-doping, respectively. The mechanism of the enhancement was discussed, that is due to the improvement of the phosphors’ crystallinity and charge compensation when the Li+ ions were introduced. Furthermore, the thermal stability of KSrPO4:0.01Dy3+, 0.06Li+ was measured and discussed, demonstrating it can be applied for high-powered LED. And the chromaticity coordinates of KSrPO4:0.01Dy3+, xLi+ can be tuned efficiently from the cold-white region to warm-white region with Li+ ions increasing, presenting its potential applied value as a new warm-white LED phosphor.

Effects of Li doping on the negative bias stress stability of solution-processed ZnO thin film transistors

To investigate the effect of Li dopant on the electrical characteristics under negative bias stress (NBS), we analysed ZnO and Li doped ZnO TFTs. The Li dopant enhanced the field effect mobility and sustained the variation in Von of the ZnO TFTs.

Effect of Li-doping on Photoluminescence of Screen-printed Zinc Oxide Films

ABSTRACTUndoped and Li-doped ZnO films were fabricated by screen printing approach on sapphire substrate. The effect of Li doping and annealing temperature on the luminescent, optical, electrical and structural properties of the films has been investigated by the photoluminescence (PL), Raman scattering, conductivity, Atomic Force microscopy and X-ray diffraction (XRD) methods. The XRD study revealed that the films have polycrystalline wurtzite structure with grain sizes ranging from 26 to 38 nm. In the undoped ZnO films, the increase of annealing temperature from 800 to 1000 °C resulted in the increase of the grain sizes, film conductivity and the intensity of the ultraviolet PL. The introduction of Li of low concentration of 0.003 wt % at 800 °C or 900 °C allows producing the low-resistive films with enhanced ultraviolet PL and reduced density of crystalline defects. Highly doped films (with 0.3 wt % of Li) were found to be semi-insulating with deteriorated PL properties irrespectively of the annealing temperature. It is shown that introduction of Li in the ZnO films affects their PL spectra mainly via the evolution of the film crystallinity and the density of intrinsic defects.