Influence of lithium doping on the structural and electrical characteristics of ZnO thin films

Thin films of undoped and lithium-doped Zinc oxide, (Zn_1 − xLi_x)O; x = 0, 0.05, 0.10 and 0.20 were prepared by sol-gel method using spin-coating technique on silicon substrates [(111)Pt/Ti/SiO₂/Si)]. The influence of lithium doping on the structural, electrical and microstructural characteristics have been investigated by means of X-ray diffraction, leakage current, piezoelectric measurements and scanning electron microscopy. The resistivity of the ZnO film is found to increase markedly with low levels (x ≤ 0.05) of lithium doping thereby enhancing their piezoelectric applications. The transverse piezoelectric coefficient, e₃₁^? has been determined for the thin films having the composition (Zn_0.95Li_0.05)O, to study their suitability for piezoelectric applications.     

Magnetic and electrical properties of lanthanum substituted yttrium iron garnets

Polycrystalline yttrium lanthanum iron garnets (Y₃La _x Fe_5-x O₁₂) with varying La substitution (0 ≤ x ≤ 0.5) have been prepared in the pellet form, and studied by X-ray diffraction, magnetization, a.c. susceptibility and electrical resistivity measurements. The lattice constants are determined and the applicability of Vegard’s law has been tested. The saturation magnetization (4 πM _S) decreases very slowly almost linearly with increasing x from x = 0.0–0.5 indicating minimal reduction in ferrimagnetism and least magnetic loss. Variation of saturation magnetic moment per formula unit at 300 K with x can be explained satisfactorily assuming the collinear spin-ordering model. The Curie temperature (T _c) reduces very slowly with increasing x, which is consistent with the observed decrease in 4 πM _S with x. The activation energy (E) decreases very slowly with increasing x for x > 0.1.     

钒硼酸钇铕荧光粉的真空紫外光谱特性研究

采用高温固相法合成了YBχV1-χO4-χ：Eu^3＋荧光粉,利用XRD变温发射光谱以及真空紫外激发的光谱对其进行研究。结果表明,在147nm的真空紫外光激发下,荧光粉的发射主峰位于619nm,与（Y,Gd）BO3：Eu^3＋相比,色纯度较好,发光亮度达86％,是彩色PDP用红色荧光粉的候选材料。     

Dielectric properties and electrical conduction in yttrium iron garnet (YIG)

The dielectric properties (dielectric constant and loss) of a single crystal of yttrium iron garnet (Y₃Fe₅O₁₂) were measured in the temperature range 77–725 K and in the frequency range 100 Hz-1 MHz. AC conductivity was derived from dielectric constant and loss. DC conductivity was measured in the temperature range 30–725 K. Thermoelectric power (TEP) was measured from 77–800 K. On the basis of the results, conduction in this garnet is interpreted as due to small polarons. The nature of conduction at different temperature ranges is discussed in the light of existing reports on defect formation.     

Investigation of the oxidation of sialons with infrared reflection spectroscopy

Hot-pressedβ-sialons (Si_6-z Al _z O _z N_8-z formed in the Si₃N₄-Al₂O₃-AIN and Si₃N₄-SiO₂-AIN systems have been investigated using infrared reflection spectroscopy (IRRS). Asz increases, the IRRS bands decrease in frequency. The decrease can be explained by the decrease in the force constants of the chemical bondings. IRRS has been applied to the study of the oxidation sialons at 1200 and 1300°C as a function of time. The technique has sensitively detected cristobalite, mullite and glass phases on the oxidized surface. This is considered to be effective for understanding the oxidation kinetics of sialons.     

Structure and electrical properties of sputtered lithium cobaltite thin films

Li_xCoO_y films with x<1 and y>2 have been prepared by radio-frequency (rf) sputtering from high temperature (HT) LiCoO₂ targets. Their structures have been examined with high resolution electron microscopy. Conductivities have been studied between 77 and 400 K. The electrochemical behaviour of film electrodes have been investigated with Li/LiClO₄-PC/Li_xCoO_y cells. The annealed films consist of nanocrystalline domains with amorphous boundaries. Electrical conductivities appear to arise from variable-range hopping (VRH) of holes. The films form good electrodes with operating potentials between 2.7 and 3.8 V. The observations have been discussed on the basis of a tentative and heuristic molecular orbital based energy band diagram.     

Domain characteristics and chemical bonds of lithium niobate

Domain characteristics such as domain shape, domain switching, and etching rate at Z-surfaces of lithium niobate (LN) single crystals are comprehensively studied from the chemical bonding viewpoint. The present work shows that the domain characteristics are closely correlated to anisotropic bonding behaviors of constituent ions, which may be regarded as a microscopic reflection of detailed conditions of the chemical bonding geometry and strength of Li⁺ and Nb⁵⁺ cations in the LN crystallographic frame.     

Temperature dependent electrical properties of co-precipitated magnesium doped lithium nanoferrites

Due to a number of unique properties, nanoferrites are considered among the most emerging materials for the manufacturing of microwave devices. In past few years, different elemental compositions of nanoferrites were fabricated for this purpose. In our work, magnesium-doped lithium ferrites (Li_2?xMg_xFe₂O_4.5?δ, where x = 0.0 to 1.0) were synthesized by using co-precipitation method in optimized conditions. Structural analysis was done by using X-ray diffraction (XRD); this data was further used to calculate the porosity, phase purity and crystallite size. The XRD results confirmed the formation of spinel structure for all the samples. The surface morphology of the prepared samples was examined by using scanning electron microscope that showed particle like morphology. Thermogravimetric analysis and differential scanning calorimetry were used to investigate the phase transition and melting point of the prepared samples respectively. The analysis showed the phase transitions at two temperature ranges and the melting point of the all the samples was above 900 °C except for composition x = 0.4. Dielectric loss, dielectric constant, AC electrical conductivity and DC electrical resistivity were studied as a function of temperature. Curie temperature was also estimated from the temperature dependent conductivity data and that were observed to be decreased with increase in Mg concentration. The result obtained from the electrical analysis of the prepared samples confirmed that they could be used in frequency dependent devices.     

Domain structure and electrical properties of Gd-and Tm-doped lithium niobate single crystals

We have grown lithium niobate single crystals doped with rare-earth elements (Gd and Tm) and have examined etch patterns on their surfaces by atomic force microscopy. The thermal stability of their regular domain structure has been assessed, and their anomalous electrical properties have been studied in the temperature range 300–380 K.     

Synthesis of europium-doped yttrium hydroxide and yttrium oxide nanosheets

A new approach has been developed for the preparation of Y(OH)₃:Eu and Y₂O₃:Eu nanosheets using the sol–gel method and hydrothermal reactions. XRD patterns showed that the product was purely hexagonal-phase Y(OH)₃. TEM images revealed that the nanosheets are square shaped (1 × 1 μm²) with a thickness of several tens of nanometers. In addition, it was found that cubic-phase Y₂O₃ nanosheets can be obtained by calcination of Y(OH)₃ at 900 °C for 1 h. More importantly, the thus-prepared Y(OH)₃:Eu and Y₂O₃:Eu nanosheet phosphors were found to exhibit a relatively high photoluminescence (PL) intensity.     

Insight of yttrium doping on the structural and dielectric characteristics of ZnO nanoparticles

We report on synthesizing rare-earth yttrium oxide-doped ZnO nanoparticles through high-energy planetary milling approach. The impact of varying dopant content in the 3.0, 5.0 to 7.0 wt% range on microstructural, optical and electrical properties of ZnO nanoparticles has been successfully explored. The XRD data showed the existence of a hexagonal wurtzite ZnO phase along with Y₂O₃ impurity peaks, and the SEM micrographs divulge the development of semi-spherical nanoparticles. The incorporation of Y₂O₃ dopant in ZnO lattice has been supported by EDS, XPS and Raman analysis. The frequency and composition dependence of dielectric parameters was investigated and interpreted according to the Maxwell Wagner model. The data revealed non-monotonic dependence of the dielectric constant (ε_r), dielectric loss (tan δ) and AC conductivity and impedance of ZnO with varying dopant content. The variation of the shape of the impedance semicircles and the equivalent circuits between pure and doped ZnO samples prove increased grain boundary resistance due to Y₂O₃ incorporation. The study reveals that Yttrium-doped ZnO nanostructures are possible potential candidates for application in electronic devices if the dopant’s content is controlled.

     

Magnetic and electrical properties of lithium borosilicate glasses containing nickel and iron oxides

Measurements of a.c. conductivity, dielectric constants, Mo¨ssbauer spectra and magnetic susceptibility were carried out on samples of composition: 20LiO₂, 31B₂O₅, 34SiO₂, 15 – x NiO, xFe₂O₃ where x = 2.5, 5, 7.5, 10 and 12.5 mol %. It was found that when x is changed from 2.5 to 10 mol % NiO, the conductivity decreases due to the increase of the bridging oxygen ions. When x is increased to greater than 10 mol % NiO, the conductivity increases because of the decrease of the ratio of Fe²⁺Fe³⁺ ions as confirmed from Mo¨ssbauer data. The conductivity has a distinct minimum at 10 mol % NiO. Distribution of relaxation processes was also studied, and two processes were adequate to describe the present experimental data.     

Memory-core characteristics of cobalt substituted lithium ferrite

The memory-core characteristics of compositions in the system Li0.47-1/2x-1/2yCoxZnyNi0.06Fe2.47-1/2x-1/2yO4have been studied. The cobalt and zinc contents have been varied from zero to 0.02 and from zero to 0.12, respectively. It is demonstrated that small amounts of cobalt decrease the temperature coefficient of the coercive force and, in the zinc-containing materials, produce improved square-loop properties. These materials demonstrate improved pulse response properties when compared with unsubstituted lithium ferrite.     

Effect of heat treatment on the electrical resistivity of lithium ferrite

Polycrystalline lithium ferrite samples were subjected to a variety of heat treatments. The most effective process in raising the sample resistivity was the oxidation process. The efficiencies of these heat treatment processes were compared. Effects of heat treatments on the thermoelectric, microwave line width, and dielectric properties of the samples were also reported.