Effects of Mg doping concentration on the band gap of ZnO/Mg x Zn1−x O multilayer thin films prepared using pulsed laser deposition method

Epitaxial ZnO/Mg _x Zn_1-x O multilayer thin films (x?=?0~0.15) were prepared on c-Al₂O₃ substrates by pulsed laser deposition and their crystallinity and optical properties were investigated using X-ray diffraction, TEM, and UV-Vis spectroscopy. ZnO/Mg _x Zn_1-x O multilayer thin films were grown by stacking alternate layers of ZnO and Mg _x Zn_1?x O with laser fluence of 3 J/cm², repetition rate of 5 Hz, substrate temperature of 600 °C, and oxygen partial pressure of 5?×?10^–4 Torr. The thickness of individual ZnO and Mg _x Zn_1?x O layers was maintained at 3 and 6 nm, respectively, and the total thickness of the films was kept in 300 nm. X-ray diffraction results showed that the multilayer thin films were grown epitaxially on c-Al₂O₃ substrates with an epitaxial orientation relationship of $\left. {\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{multilayer}}} } \right\|\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} } $ . Cross-sectional TEM micrographs showed alternating layers of bright and dark contrast, indicating the formation of ZnO/Mg _x Zn_1?x O multilayer thin films. The 2θ value of Mg _x Zn_1?x O (0002) peak increased from 34.30° at x?=?0 to 34.67° at x?=?0.15 with increasing Mg doping concentration in the multilayer thin films. The absorption edge in the UV-Vis spectra shifted to shorter wavelength from 360 at x?=?0 to 342 nm at x?=?0.15 and the band gap energy increased from 3.27 eV at x?=?0 to 3.54 eV at x?=?0.15.     

Ferroelectric properties of Ba1−x Sr x TiO3 thin films synthesized by using novel sol–gel technique through carbonates

Ba_1?x Sr _x TiO₃ (BST) thin films were prepared on the substrate of Pt/Ti/SiO₂/Si by using novel sol–gel process through carbonates. The surface morphology and domain contrast of the films were investigated by atomic force microscopy (AFM), and the domain structures of the BST film were observed when AFM were operated in piezoelectric force microscopic (PFM) analysis and in the friction mode (FFM). The ferroelectric properties of the films were also investigated. It is shown that BST films obtained by the new sol–gel process through carbonates exhibit good properties.     

The microstructures and dielectric properties of xSrZrO3–(1−x)SrTiO3 ceramics

In this paper, the microstructures and the dielectric properties of xSrZrO₃–(1?x)SrTiO₃ (x?=?0.01, 0.03, 0.05, and 0.07) ceramics were investigated. The composition can form a single-phase structure solid solution as x increases from 0.01 to 0.07, and the average grain size decreases from 15 to 2 μm with the x increasing. With the variation of SrZrO₃ content, dielectric constant, dielectric loss, and breakdown strength (BDS) of xSrZrO₃–(1?x)SrTiO₃ samples are changed. When x?=?0.05, the samples exhibit high BDS more than 14 kV/mm and low dielectric loss about 1?×?10^?3 with dielectric constant of 330. It can be a candidate material of energy storage for pulsed power application.     

Characterization of luminescent properties of Sr–Ca–Al–O multi-phases oxide phosphors

Multi-phases phosphors, which could exhibit red, green, and blue emission bands simultaneously, were synthesized by the solid-state reaction method with a flux. Starting materials of SrCO₃, CaCO₃, and Al₂O₃ were mixed and fired. H₃BO₃ and Eu₂O₃ were added as a flux and a dopant, respectively. Effects of the excitation energy and the mixing ratio of starting materials on the luminescent properties were investigated. Phase transformations and variations of luminescent properties were also observed as a function of H₃BO₃ flux amounts. Emission wavelength and intensity depended on the excitation energy as well as H₃BO₃ flux amounts. The mixture of 8SrCO₃–4CaCO₃–11Al₂O₃–0.8H₃BO₃–0.18Eu₂O₃ showed red, green, and blue emission by exciting at near UV, while 8SrCO₃–4CaCO₃–11Al₂O₃–1.2 and 1.6H₃BO₃–0.18Eu₂O₃ exhibited strong red emissions.     

Properties of CaTi1 − x Fe x O3 − δ Ceramic Membranes

CaCO₃, TiO₂ and Fe₂O₃ were mixed in the appropriate stoichiometric quantities and calcined at 1100C for 10 h. These powder mixtures were uniaxially pressed and sintered at temperatures ranging from 1350 to 1500_C for 2 h in order to obtain dense disk-shaped samples with nominal CaTi_{1 – x}Fe_xO_3– (x = 0.05, 0.15, 0.20, 0.40 and 0.60) compositions. Dilatometry and in situ high temperature powder X-ray diffraction analysis showed a good agreement on the thermal expansion behaviour of these materials between room temperature and 1000_C. The estimated linear thermal expansion coefficient is close to 13× 10^{– 6} K^{– 1} and is little affected by composition. No evidence for surface carbonation was detected in the infrared spectra collected on samples previously annealed in CO₂ atmospheres. The oxygen permeability measured at temperatures ranging from 750 to 1000_C goes through a sharp maximum for x = 0.20. This result is interpreted by structural differences related to change from disordered to ordered oxygen vacancies. The overall performance of CaTi_0.80Fe_0.20O_3– is compared to other mixed conducting materials.     

Features of Charging–Discharging of Supercapacitors

We present the results of experimental investigations of supercapacitors produced by Panasonic using several methods, namely, measurements of temporal dependences of charging–discharging currents, cyclic dc charging, and cyclic voltammetry. The values of the internal resistance, static and dynamic capacitance, as well as their dependences on the bias voltage of the capacitors, have been determined. Measurements have shown that the initial stage of relaxation of current is well approximated by the exponential time dependence, and then transition to a powerlike dependence occurs. This well-known effect is explained on the basis of the allowance for specific transport properties of a porous fractal-type medium. These processes are adequately described by the fractional-differential model of anomalous diffusion. A weak dependence of relaxation curves on the voltage at low values of the latter (<3 V) and the change in the power-law exponent at elevated voltages (>3 V) is explained by the appearance of new percolation paths blocked at low charging voltages due to the presence of high-potential barriers. The internal resistance and the static capacitance have been determined by measuring the voltage across the supercapacitor in the mode of dc charging. These parameters have been shown to depend on the voltage applied to the capacitor. The dependence of the dynamic capacitance on the voltage has been determined using cyclic voltammetry. It has been shown that the capacitance depends not only on the voltage, but also on the prehistory of charging and discharging of the capacitor. Comparison of the experimental results and the published data on the models and equivalent circuits with passive R, L, and C elements allows one to conclude that such models and equivalent circuits can be applied only when explaining a limited number of phenomena, in particular, behavior at small relaxation times.     

Dielectric Properties of Bi4−x La x Ti3O12 (0 ≤ x ≤ 2) Ceramics

The dielectric properties of the Bi_4–x La _x Ti₃O₁₂ (0 x 2) ceramics were characterized and discussed together with the P-E relation (polarization vs. electric field). With increasing x, the P-E relation changed from normal ferroelectric hysteresis loops to pure linear relation, which indicated that La³⁺ substitution for Bi³⁺ in Bi₄Ti₃O₁₂ induced a phase transition from ferroelectric to paraelectric state at ambient temperature. Low loss dielectric ceramics with temperature stable dielectric constant were obtained for x > 1.2 in Bi_4–x La _x Ti₃O₁₂ at 1 MHz. And the loss increased in all the compositions when the ceramics were measured at microwave frequencies.     

MPB Phase Transition and Microstructure of (1 – x)PMN–xPZT Activated by 0.05BZN Ceramics

The relaxor ferroelectric materials can be found in morphotropic phase boundary (MPB) existing between tetragonal and cubic phase. Since the MPB shifts to other phases by adding ceramics composition. [(1 – x)Pb(Mg_1/3 Nb_2/3)O₃–x Pb(Zr_0.52Ti_0.48)O₃] were doped by 0.05Ba(Zn_1/3 Nb_2/3)O₃ when x = 0.4, 0.3, and 0.2 ceramics, which prepared by using a two–step sintering process. The MPB transitions were studied by the use of XRD. The samples, at x = 0.4, were in MPB and then gradually shifted to cubic phase at x = 0.2. The microstructure of samples fracture found that the largest grain size of 4.51 μm for x = 0.2. This study using TEM technique which demonstrated a crystalline morphology with the largest crystal size about 1.293 μm at x = 0.3. These results also revealed that not only the ferroelectric phase shifted to relaxor behavior with decreasing PZT contents in PMN–PZT system but also activated by BZN, which led to the presence of the relaxor behavior.     

Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders

Studies on the Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders. The crystal structure and microstructure of Ba_0.60Sr_0.40TiO₃ ceramics doped with Mg has been investigated. The microwave complex permittivity of BST ceramics doped with Mg powders is investigated in 100 MHz–6 GHz ranges by coaxial-transmission technique and the calculation of the equivalent medium theory. Experimental results showed that the typical cubic phase structure and the diffraction peaks of secondary phase that MgO phase become stronger with increasing Mg²⁺ content in the XRD pattern of the Mg doped BST ceramic sintered at 1250°C. The real part of the microwave complex permittivity of BSTM30 ceramic powders is excellent described by results of calculation of Bruggeman theory in wide powder content.     

Synthesis and piezoelectric properties of (1 − x)(Na0.5K0.5)NbO3–x(Ba0.95Sr0.05)TiO3 ceramics

(1 ? x)(Na_0.5K_0.5)NbO₃–x(Ba_0.95Sr_0.05)TiO₃ [(1 ? x)NKN–xBST] ceramics were synthesized by the conventional solid-state sintering, and their microstructure and piezoelectric properties were investigated. The sintering temperature of the specimens was 1075 °C in air atmosphere and a morphotropic phase boundary (MPB) was observed in the specimens with 0.03 ≤ x ≤ 0.05. Compared with the piezoelectric properties of the NKN ceramics, the enhanced d ₃₃ value of 136 pC/N and ? ₃ ^T /? _o value of 671 were obtained for the (1 ? x)NKN–xBST specimens with x = 0.03.     

Structure and dielectric properties of Bi5−x La x Nb3O15 ceramics

Bi_5?x La _x Nb₃O₁₅ (x?=?0–?1.25) ceramics prepared by conventional solid-state reaction were studied using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and dielectric spectroscopy techniques. The XRD analysis indicated single phase solid solution of Bi_5?x La _x Nb₃O₁₅ is formed for x?≤?1.25. EPMA showed good densification and homogeneous microstructures for the ceramics. With increasing x, the dielectric constant decreases monotonously and can vary from 258 to 158 at 300 kHz. The frequency dependence of dielectric constants indicated these ceramics are promising candidates for high frequency applications.     

Study of polycrystalline Ba1−x Ca x MoO4 films prepared by electrochemical technique

The polycrystalline Ba_1?x Ca _x MoO₄ films were prepared directly on molybdenum substrates by electrochemical technique. The growing characteristics of the films were studied by scanning electron microscopy (SEM), x-ray diffraction (XRD), and energy dispersive x-ray analysis (EDRX) techniques, respectively. The SEM images show that the morphology of the Ba_1?x Ca _x MoO₄ film is affected significantly by the composition of the films when the process parameters are preset. The XRD and EDRX analyses reveal that the compositions of the films are strongly controlled by the capability of bond between cation and anion, besides the cation concentration, temperature, and current density, in such situation.     

Raman Scattering Study of the Pb(Hf x Ti1−x )O3 Ceramics

Raman spectroscopy was used to study the long wavelength vibrations of tetragonal perovskite (space group P4mm) Pb(Hf_xTi_1–x)O₃ (PHT) (0.10 x 0.50) samples at room temperature and at 20 K. For x 0.40, Raman spectra collected from the PHT samples were very similar to the previous spectra collected from the PZT samples with the same value of x, except the mode at around 190 cm^–1, whose frequency was decreasing with increasing x in PHT ceramics. Correspondingly, the latter feature was taken as a sign of the mass effect (Hf versus Zr) while the similarity of the remaining parts of the Raman spectra was assumed to be due to the almost identical ionic radii difference between Ti⁴⁺ and Zr⁴⁺ and between Ti⁴⁺ and Hf⁴⁺ ionic radii. The behaviour of the mode at around 280 cm^–1 revealed that a phase transition occurred once x was changing from 0.40 to 0.50.     

Structure and microwave dielectric properties of Sm(2−x)/3Li x TiO3

The structural evolution, and microwave dielectric properties of ceramics (x = 0.0 ≤ x ≤ 0.5) were investigated in this work. X-ray diffraction (XRD) results show that samples with x > 0.3 exhibit a single perovskite phase. Impurity phases of Sm₂Ti₂O₇ and TiO₂ appear and their amount increases with the decrease of x when x ≤ 0.3. TEM observation indicates that the A-site is ordered in x = 0.5, but not in x = 0.3). The dielectric constant decreases with the increase of x for 0.1 ≤ x ≤ 0.4 and then increases with further increase in x up to x = 0.5. The Q×f value decreases with the decrease of x due to the increased occurrence of Sm₂T₂O₇ secondary phase, defects and twinning boundaries. The temperature coefficient of resonant frequency is negative and its absolute value decreases greatly with the decrease of x value.     

Effect of additive SrWO4 on microwave dielectric properties of SrTiO3–Sr(Mg1/3Nb2/3)O3 ceramics

The crystal structure and the properties of a new microwave dielectric ceramics x SrTiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ have been investigated. With x?=?0.025, The new microwave dielectric ceramic achieves the dielectric properties of a dielectric constant ? _r ～27.8, a Q?×?f value ～26,800, and a τ _f value ～7.4 ppm/°C. When the SrWO₄ is added, the sintering temperature of x SrTiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ ceramics will fall to 1350 °C, and its Q?×?f value can be improved further and the τ _f value becomes smaller. When the SrWO₄ is added by 0.07 mol, the specimen acquires the following microwave properties: a dielectric constant ? _r ～30.3, a Q?×?f value ～29,500, and a τ _f value of approximately ?0.4 ppm/°C.     

Electrochemical evaluation of La1 − x Ca x CoO3 cathode material for zinc air batteries application

We synthesized nano-sized La_1???x Ca _x CoO₃ (x?=?0.1–0.4) cathode catalysts for zinc air secondary batteries by the citrate method, and measured electrochemical characteristics of the cathodes according to the cathode catalyst’s calcium content. We heat treated the prepared precursor at a calcination temperature of 700°C, and examined it by XRD analysis and electrochemical evaluation. We examined the prepared La_1???x Ca _x CoO₃ catalyst powder’s oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and cycle-stability performance. When we consider ORR, OER and cycle-stability performance simultaneously, La_0.9Ca_0.1MnO₃ catalyst showed the best performance because of its lowest voltage deference between charge and discharge, and its lowest degradation according to cycle.     

Low-temperature sintering and dielectric properties of the Bi(Nb1−x Ta x )O4 system

Low-temperature sintering and dielectric properties of the Bi(Nb_1?x Ta _x )O₄ (x?=?0.1, 0.3, and 0.5) system was investigated as a function of the zinc borosilicate (ZBS) glass content with a view to applying this system to LTCC technology. The addition of 7 wt% ZBS glass ensured a successful sintering below 900°C. The complete solid solution of Bi(Nb, Ta)O₄ with an orthorhombic structure was formed and the high temperature form of Bi(Nb, Ta)O₄ with a triclinic structure was not observed. The second phase of Bi₂SiO₅ was observed for all compositions. The non-relative liquid phase sintering (NLPS) occurred and the one-stage sintering was conducted. The Q?×?f values were improved by the addition of Ta. Bi(Nb_0.7Ta_0.3)O₄ with 7 wt% ZBS glass sintered at 900°C demonstrated 35.8 in the dielectric constant (? _r), 2,200 GHz in the quality factor (Q?×?f ₀), and ?48 ppm/°C in the temperature coefficient of resonant frequency (τ _f).     

Ferroelectric Characteristics of Bi 4−x La x Ti 3 O 12 Thin Films Crystallized at Low Temperetures

Recently, Bi 4 m x La x Ti 3 O 12 (BLT) has received much attention because it enables low crystallization temperature with a large remanent polarization. BLT films were prepared using a metal organic decomposition technique followed by a rapid thermal annealing (RTA) and a furnace annealing. The annealing of BLT was performed in the temperature range from 550 to 700C. In particular, BLT film annealed at 600C using the RTA tool and the furnace shows good ferroelectric characteristics. The BLT film annealed at 600C exhibits a large value of remanent polarization (22 w C/cm 2 at 250kV/cm), and a low leakage current density (7 2 10 m 7 A/cm 2 at 250kV/cm), a good endurance characteristics for up to 3.2 2 10 11 cycles at 250kV/cm at 85C. From an accelerated imprint test, the lifetime of hysteresis integrity is estimated to be over 10 years at 85C. In conclusion, BLT is the one of the promising material to achieve the high density FeRAMs.     

Chemical Solution Deposition of Epitaxial La1−x (Ca, Sr) x MnO3 Thin Films

We report on the epitaxial growth of magnetoresistive La_0.7Ca_0.3MnO₃ and La_0.7Sr_0.3MnO₃ thin films by chemical solution deposition. Thin films were prepared by spin-coating of single-crystal LaAlO₃ (100) substrates with precursor solutions of different concentrations and crystallized at 850°C. The structure of the thin film was found to be influenced by the concentration of the spin-coating solution. The thin film structure and epitaxy was clearly improved by reducing the concentration of the precursor solution. All thin films displayed excellent electrical properties such as a low resistivity and very high metal-insulator transition temperatures T _MI .     

The effects of the LaNiO3 interlayer in the preferential orientation and the dielectrical properties of Ba x Sr1− x TiO3 thin films

Ba _x Sr_1?x TiO₃ (BST) thin films were grown on different substrates with or without LaNiO₃ (LNO) layer by a modified sol–gel process. The BST thin films obtained have full perovskite phase with dense and crack-free surface. BST thin films on different substrates with LNO layer show (100) preferential orientation, the texture coefficient (TC) value is calculated to be about 42.7%, whereas those without LNO layer show a fairly reduced preferential orientation, the TC value is just about 24.8%. It is considered that the preferential orientation is induced by the interface stress between LNO and BST. Electrical property measurements showed that BST thin film with a LNO interlayer has lower capacitance and larger dielectric loss, which is due to smaller grains of the thin film.