Microelectrodes for local conductivity and degradation measurements on Al stabilized Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript> garnets

The attractiveness of Li₇La₃Zr₂O₁₂ (LLZO) cubic based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relations between composition and conductivity as well as degradation effects are still not completely understood. In this contribution we demonstrate the applicability of microelectrodes (Ø = 20–300 μm) for electrochemical impedance spectroscopy (EIS) studies on LLZO garnets. Microelectrodes allow to obtain local information on the ionic conductivity. A comparison between the overall performance of the sample (3.3 × 10^?4 S cm^?1) and local measurements revealed differences in conductivity with a maximum of the locally measured values of 6.3 × 10^?4 S cm^?1 and a minimum of 2.6 × 10^?4 S cm^?1. One reason behind these conductivity variations is most probably a compositional gradient in the sample. In addition, microelectrodes are very sensitive to conductivity changes near to the surface. This was used to investigate the effect of moisture in ambient air on the conductivity variations of LLZO. Substantial changes of the measured Li-ion transport resistance were found, particularly for smaller microelectrodes which probe sample volumes close to the surface.     

Investigation on FTIR spectra of barium calcium titanate ceramics

Barium titanate, which is applied in many fields, is a kind of very important ferroelectric material because it is lead free. Its physical properties are changed by replacement or addition of other ions. Here, barium calcium titanate ((Ba,Ca)TiO₃) ceramics are prepared. The concentration of calcium is up to 20 at.%. The Fourier transformation infrared spectroscopy (FTIR) measurement is carried out in order to reveal the vibration of crystal lattices. The influence of the replacement on the interaction between Ti and O can be observed by investigating the absorption peak of the Ti–O bond. The wavenumber of absorption peak of Ti–O bond becomes larger with increase of the content of Ca, even though the concentration of Ti is not changed. The wavenumber of absorption peak in (Ba_0.95Ca_0.05)TiO₃ is near 525 cm^?1 while that in (Ba_0.80Ca_0.20)TiO₃ is near 550 cm^–1. It is attributed to the decrease of the cell size. The length of Ti–O bond is shortened by replacement of Ca. Then the interaction between Ti and O is enhanced. The similar phenomenon is observed in (Ba,Mg)TiO₃ and alkali doped BaTiO₃ materials as well, supporting the mechanism. Furthermore, the aging effect in (Ba,Ca)TiO₃ and (Ba,Mg)TiO₃ systems is observed. The former exhibits a good stability when the latter shows unstable FTIR spectra. The influence of point defects on the aging effect is discussed. These results indicate that the FTIR measurement is helpful to study the relationship between the structure and physical properties of ferroelectric materials.     

Effects of cobalt addition on structural,thermal and electrical properties of praseodymium-yttrium co-doped barium cerates

Effects of cobalt addition on structural, thermal and electrical properties of praseodymium-yttrium co-doped barium cerates have been investigated. Relative densities >98 % have been achieved after sintering at 1400 °C or 1500 °C for only 1 h. All studied compounds are stable in ambient air up to the measured 900 °C and, in reducing atmosphere (both wet and dry 5 % H₂-Ar) up to the measured 800 °C. The Co-free sample (BaCe_0.7Y_0.2Pr_0.1O_3-δ) exhibits the highest conductivity of 1.21?×?10^?2 S cm^?1 at 700 °C in air while the corresponding cobalt containing sample (BaCe_0.7Y_0.175Pr_0.1Co_0.025O_3?δ) has a conductivity of 9.85?×?10^?3 S cm^?1 at 700 °C in air. Cobalt addition allows the ability to retain much larger amounts of water to be retained as suggested by the higher conductivities obtained in wet hydrogen compared to the values in dry reducing atmosphere. This latter phenomenon is of special interest as it suggests the possibility of higher ionic conductivities in water-containing atmosphere and would benefit to intermediate- and high-temperature solid oxide fuel cells and/or electrolysers. The thermal expansion coefficients for the Co-free and Co-containing samples were around 12.0?×?10^?6 K^?1 between 25 and 1000 °C.     

Ultra-thin lead titanate films prepared by tripole magnetron sputtering

Abstract

Ultra-thin lead titanate (PbTiO₃) films of 6 to 80 nm in thickness were deposited on single crystal MgO (100) substrate by employing tripole magnetron sputtering system, which was deviced to make the erosion area on the co-axial targets movable, and hence make a layer-by-layer process realized. Thin films of PbTiO₃ with highly-oriented perovskite single phase were obtained at substrate temperature of 550°C. In the films thicker than 20 nm, the X-ray diffraction showed clearly the separated (100) and (001) peaks, while in those thinner than 10 nm, two peaks seemed to be superimposed onto a single peak, suggesting a gradual transition into pseudocubic. Far-infrared spectroscopy indicated a thickness-dependent absorption at wavenumber of 85 cm^?1, which may be attributed to the phonon related to the Pb-TiO₆ vibration.     

Structural and electrochemical properties of LiNi0.7Co0.15Mn0.15O2 thin film prepared by high frequency hybrid direct current and radio frequency magnetron sputtering

A LiNi_0.7Co_0.15Mn_0.15O₂ thin film cathode has been successfully prepared by hybrid direct current - radio frequency magnetron sputtering onto glass substrate from the LiNi_0.7Co_0.15Mn_0.15O₂ target and post-annealed by the rapid thermal annealing process. Its structure and morphology were characterized by X-ray diffraction, and scanning electron microscopy while its chemical compositions were confirmed with the inductively coupled plasma atomic absorption spectrophotometer, Raman spectroscopy, Auger electron spectroscopy, and glow discharge spectrometer. Its electrochemical properties were measured by galvanostatic charge - discharge test and cyclic voltammetry. First discharge capacity of 73 μAh?cm^?2?μm^?1 was obtained from a half cell with the LiNi_0.7Co_0.15Mn_0.15O₂ thin film cathode and lithium metal anode in the potential range of 4.3?~?2.5 V at 30 μA and its coulombic efficiency was more than 99 %.     

Electroless nano zinc oxide–activate carbon composite supercapacitor electrode

An electroless deposition process was used to synthesize the nanostructured zinc oxide (ZnO)–activated carbon (AC) as supercapacitor. The composite oxide was studied by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction analysis (XRD). The electrochemical performance of the nanocomposite was analyzed through cyclic voltammetry (CV) and AC impedance spectroscopy (EIS) in 0.1 M Na₂SO₄ as electrolyte. A specific capacitance 187 F g^?1 at a scan rate of 5 mV s^?1 was obtained using cyclic voltammetry (CV) and a nearly rectangular shaped CV curve was observed for the composite oxide. The supercapacitor was quite stable during charge–discharge cycling and exhibited constant capacitance during the long-term cycling. It also yielded a specific capacitance 171 F g^?1 at 5 mA cm^?2 with a high energy density of 21.9 Wh kg^?1 and 4.2 kW kg^?1 of power density. Due to unique structure of prepared ZnO–AC nanocomposite, it is a promising candidate for supercapacitor.     

Preparation, microstructure and electrical properties of Li1.4Al0.4Ti1.6(PO4)3 nanoceramics

NASICON-type Li_1.4Al_0.4Ti_1.6(PO₄)₃ solid electrolytes were prepared by various processes, such as crystallization of glasses, spark plasma sintering (SPS) and conventional sintering process from nanosized precursor powders synthesized by a sol–gel route. The experimental results showed that grain size and relative density were the main factors determining the ionic conductivity of the bulk materials. The SPS technique produced ceramics with nearly 100% of the theoretical density. Maximum room temperature conductivities, 1.39?×?10^?3 S cm^?1 and 1.12?×?10^?3 S cm^?1 of grain boundary conductivity and total conductivity, respectively were obtained which were the highest values for Li⁺ inorganic oxide conductors as reported. Crystallization of ceramics from a glass was also certified as a favorable route to fabricate a bulk material with high conductivity.     

Effect of composite electrode thickness on the electrochemical performances of all-solid-state li-ion batteries

Several ceramic half-cells with differing electrode composite thicknesses but identical formulations were assembled using the spark plasma sintering (SPS) technique, in order to conduct comparable investigations of their kinetic limitations. The SPS technique was used to assemble the composite electrode and the electrolyte together within a few minutes. NASICON-type Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) ceramic was used as solid electrolyte, as it offers high ionic conductivity (3 × 10^?4 S.cm^?1 at 25 °C) with a Li⁺ transport number of 1. LiFePO₄ active material was used as a model material; it offers an average flat potential of 3.45 V vs Li⁺/Li and a reasonably high theoretical capacity of 170 mAh.g^?1. Surface capacity values (from 0.8 to 3.5 mAh.cm^?2), which are proportional to electrode thickness, remained quite close to the initial values after more than 20 cycles, even for a 325 μm thick electrode (3.5 mAh.cm^?2). The overpotential in the flat plateau region was proportional to the current density used, which means that it was dependent only on the cell’s ohmic drop. Performances were not limited by the ion transport into the solid electrolyte and composite electrode volume - as in classical Li-ion batteries - since the transport number of LAGP is one. Therefore, very thick electrode-enabling batteries with high-surface capacity can be considered.     

Improvement of a GDC-based composite cathode for intermediate-temperature solid oxide fuel cells

La_0.84Sr_0.16MnO_3?δ - Ce_0.8Gd_0.2O_2-δ (LSM-GDC) composite cathodes were fabricated by impregnating the LSM matrix with both LSM′ (La_0.84Sr_0.16MnO_3?δ) and GDC (or only GDC), and the ion-impregnated LSM-GDC composite cathodes showed excellent performance. At 750 °C, the value of the cathode polarization resistance (R _p ) was only 0.058 Ω cm² for an ion-impregnated LSM-GDC composite cathode which was impregnated with both LSM′ and GDC. For the performance of the single cell with the same cathode, the maximum power density was 1.1 W cm^?2 at 750 °C. The long-term test of the cell was carried out at 700 °C with a constant load of 0.3 A cm^?2 and the output voltage was stable on the whole. The results demonstrated that LSM-GDC fabricated by impregnating the LSM matrix with both LSM′ and GDC was a promising composite cathode material for the intermediate-temperature solid oxide fuel cells.     

Hydrothermal synthesis of LiFePO4 with small particle size and its electrochemical properties

Lithium iron phosphate (LiFePO₄) powders were prepared by hydrothermal reactions under a nitrogen atmosphere or an air atmosphere, and the microstructure and electrochemical properties of the LiFePO₄ powders were investigated. The LiFePO₄ powder prepared under the nitrogen atmosphere (LiFePO₄–N₂) had a small particle size in the range of 300–500 nm, whereas the powder prepared under the air atmosphere (LiFePO₄?air) had a large particle size in the range of 1–5 μm. Although the Fe²⁺/Fe³⁺ ratio was not significantly different in both LiFePO₄ powders, the Fe²⁺/Fe³⁺ ratio in the precursor suspension prepared under the nitrogen atmosphere was much higher than that prepared under the air atmosphere, thereby resulting in the small particle size of the LiFePO₄–N₂ powder. The discharge capacity of a LiFePO₄–N₂ electrode was 149 mAh g^?1 at a low current density of 10 mA g^?1, whereas that of a LiFePO₄?air electrode was 83 mAh g^?1. Impedance analyses indicated that the charge transfer resistances normalized to the surface area of LiFePO₄ particles for the LiFePO₄–N₂ and LiFePO₄?air electrodes were 4.6 and 4.8 Ω m², respectively. These values were not significantly different. This revealed that the factor dominating the electrochemical properties of LiFePO₄–N₂ and LiFePO₄?air powders was particle size and not crystalline lattice or Fe²⁺ concentration.     

Composition-dependent dielectric properties and energy storage performance of (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics

In this work, Pb_0.97La_0.02(Zr _x Sn_0.95?x Ti_0.05)O₃ (PLZST) (0.5?<?x?<?0.9) tetragonal antiferroelectric (AFE_T) and orthogonal antiferroelectric (AFE_O) ceramics were successfully fabricated by screen printing process. The ceramic materials were in thick-film form bonded with a small amount of glass. The electric field up to 400 kV/cm was presented for antiferroelectric ceramics. Besides, in order to reduce the energy loss of ceramics, the effects of Sn content and temperature on the dielectric properties and energy storage performance of AFE ceramics were investigated. With the increase of Sn content, the forward threshold electric field (E _AF) and backward threshold field (E _FA) decreased and the energy storage density increased obviously. The maximum energy storage density of 5.6 J/cm³ (30 °C) and 4.7 J/cm³ (120 °C) with corresponding energy efficiency of 67 % and 73 % were obtained in Pb_0.97La_0.02(Zr_0.5Sn_0.45Ti_0.05)O₃ ceramic, which makes this material a promising potential application in capacitors for pulsed power systems.     

Effects of transition metal (Ni, Mn, Cu) doping on ferroelectric properties of Bi0.9Nd0.1FeO3 thin films prepared by chemical solution deposition method

Transition metal (Ni, Mn, Cu) doped Bi_0.9Nd_0.1FeO₃ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to pure BiFeO₃ (BFO) thin film, improved ferroelectric and leakage current properties were observed in the transition metal doped thin films. The values of remnant polarization (2P _r ) and coercive electric field (2E _c ) of the transition metal doped thin films were 59 μC/cm² and 690 kV/cm at 700 kV/cm for the Ni-doped Bi_0.9Nd_0.1FeO₃ thin film, 57 μC/cm² and 523 kV/cm at 670 kV/cm for the Mn-doped thin film, and 85 μC/cm² and 729 kV/cm at 700 kV/cm for the Cu-doped thin film, respectively. The 2P _r values observed in the transition metal doped thin films were much larger than that of the BFO thin film, 21 μC/cm² at 660 kV/cm. Also the 2E _c values of in the transition metal doped thin films were lower than that of the BFO thin film, 749 kV/cm at 660 kV/cm. The reduced leakage current density was observed in the transition metal doped thin films, which is approximately two orders of magnitude lower than the BFO thin film, 2.6?×?10^?3 A/cm² at 100 kV/cm.     

Structural and improved electrical properties of rare earth (Sm, Tb and Ho) doped BiFe0.975Mn0.025O3 thin films

Pure BiFeO₃ (BFO) and rare earth (RE) ion co-doped (Bi_0.9RE_0.1)(Fe_0.975Mn_0.025)O₃ (RE?=?Sm, Tb and Ho, denoted by BSFM, BTFM and BHFM) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of distorted rhombohedral perovskite structure for the thin films were confirmed by using an X-ray diffraction and a Raman scattering analysis. Microstructural features for the thin films were examined by using a scanning electron microscopic analysis. Among the thin films, the lowest leakage current density of 1.22?×?10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2Pr) of 72.4 μC/cm² and low coercive field (2E _c ) of 689 kV/cm (at 980 kV/cm) were measured for the BTFM thin film.     

Structural, dielectric and electrical studies of MgAl2−2xY2xO4 (x = 0.00–0.05) cubic spinel nano aluminate

Investigations were carried out on a series of MgAl_2-2xY_2xO₄ (x?=?0.00–0.05) nanoparticles prepared in steps of 0.01 by chemical co-precipitation method to study the effect of yttrium substitution at aluminum site on the structural, dielectirc and electrical properties. The single phase cubic spinel structure of all the samples was confirmed by X-ray diffraction (XRD). The Fourier transform infrared spectroscopy (FTIR) study shows two strong absorption bands in the frequency range 400–800 cm^?1, on the tetrahedral and octahedral sites respectively. Elemental analysis by Energy dispersive X-ray fluorescence (EDXRF) shows that samples are stoichiometric. The scanning electron microscopy (SEM) study reveals surface morphology of nanoparticles. Transmission electron microscopy (TEM) study shows the individual nanoparticles size and validates the nanocrystalline nature of the samples. The variation of dielectric permittivity at room temperature as a function of frequency (1 KHz to 1 MHz) suggests the dielectric dispersion due to Maxwell-Wagner Interfacial Polarization. AC conductivity study reveals that the conduction is due to small polaron hopping. The electrical modulus analysis shows that nanocrystalline MgAl_2?2xY_2xO₄ system exhibits non Debye type relaxation. The dc resistivity was found to increase with increase in yttrium content.     

Flame spray synthesis and characterisation of stabilised ZrO2 and CeO2 electrolyte nanopowders for SOFC applications at intermediate temperatures

Zirconia (Y_0.16Zr_0.84O₂, Sc_0.2Zr_0.8O₂ and Sc_0.2Ce_0.01Zr_0.79O₂) and ceria (Gd_0.2Ce_0.8O₂) based electrolyte materials are synthesised at production rates up to 260 g h^?1 by a liquid-fed one-step flame spray synthesis from water-based solutions, or cost-effective rare earth nitrates with a high water content. It was found that this one-step synthesis, based on an acetylene-supported flame is able to produce phase pure and highly crystalline, nanoscale electrolyte materials. The as-synthesised powders show a cubic lattice structure independent of production rates. Specific surface areas of the powders were adjusted between 20 and 60 m² g^?2, where the latter is an upper limit for the further processing of the powders in terms of screen printing. The influence of process parameters on morphology, particle size, composition, crystallinity, lattice parameter, shrinkage behaviour and coefficient of thermal expansion of the as-synthesised powders were systematically investigated by transmission electron microscopy (TEM), nitrogen adsorption (BET), X-ray diffraction (XRD) and dilatometry. Electrochemical impedance spectroscopy (EIS) was applied at temperatures between 300 °C and 900 °C and confirmed the high quality and the competitive electrochemical behaviour of the produced powders.     

Self-assembly and hydrothermal technique syntheized Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-RGO nanocomposite: The enhancement effect of electrochemical simultaneous detection of honokiol and magnolol

The nanocomposite of Fe₂O₃-reduced graphene oxide (Fe₂O₃-RGO) was synthesized by a hydrothermal reduction using self-assembly of Fe(OH)₃ colloidal suspension and graphene oxide (GO) as precursors at 180°C. The resulting composites were characterized using XRD, SEM, FTIR, and TGA, and then were used to modify the glassy carbon electrode (GCE). After optimizing the parameters, the electrochemical behavior of honokiol and magnolol on different types of electrode was compared, which indicated that the Fe₂O₃-RGO composite-modified GCE enhanced electrochemical catalysis effect on the simultaneous determination of honokiol and magnolol. In pH 6.4 PBS solution, two well-shaped oxidation peaks at 0.51 and 0.64 V were observed at the Fe₂O₃-RGO composite-modified GCE and two well-shaped oxidation peaks were separated absolutely, which eliminated the disturbance between them. A sensitive and simple electrochemical method was proposed for the simultaneous determination of honokiol and magnolol. As to honokiol, the calibration curve is from 1.5 × 10^?8 ~ 3.3 × 10^?5 M, and the detection limit is 9.64 × 10^?9 M. For magnolol, the linear range is from 7.5 × 10^?8 ~ 2.6 × 10^?5 M, and the detection limit is 1.05 × 10^?8 M.     

Ionic conduction and crystal structure of aluminum doped NASICON-type LiGe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic crystallized at different times and temperatures

In this communication, NASICON-type glass-ceramic (lithium germanium phosphate, LiGe₂(PO₄)₃) was prepared as lithium super ionic conductor using aluminum as dopant for ionic conduction improvement. The solid solution was Li_1?+?xAl_xGe_2-x(PO₄)₃ (x?=?0.5) that Ge⁴⁺ ions were partially substituted by Al³⁺ ions in crystal structure. Initial glasses were converted to glass-ceramics at different times and temperatures for maximum ionic conduction achievement. The crystals were characterized by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), Differential Scanning Calorimetry (DSC) and Complex Impedance Spectroscopy (CIS) methods. The maximum lithium ion conductivity for glass-ceramic, 5.32?×?10^?3 S/cm at 26 °C was obtained for specimen crystallized at 850 °C for 8 h with minimum activation energy of 0.286 eV. Increasing the crystallization temperature results in secondary phase formation in grain boundary and increasing in crystallization time results in microcracks formation in specimen. Both phenomena decreased the ionic conductivity.     

Sol-gel PZT and Mn-doped PZT thin films for pyroelectric applications

Abstract

Thin films of ferroelectric lead zirconate titanate (PbZr_0.3Ti_0.7O₃ PZT30/70) and manganese doped lead zirconate titanate ((Pb(Zr_0.3Ti_0.7)_1?xMn_x)O_{3 ? x} = 0.01, PM01ZT30/70 and x = 0.03, PM03ZT30/70) have been prepared using sol-gei processing techniques. These materials can be used as the pyroelectric thin films in uncooled infrared (IR) detectors. Films deposited on Pt/Ti/SiO₂/Si substrates and annealed on a hot plate at 530°C for 5 min were seen to fully crystallize into the required perovskite phase and showed excellent ferroelectric behavior, demonstrated by reproducible hysteresis loops (P_r = 33 to 37 μC/cm², Ec(+) = 70 to 100 kV/cm, E_c(-) = -170 to -140 kV/cm). The pyroelectric coefficients (p) were measured using the Byer-Roundy method. At 20°C, p was 2.11×10^?4 Cm^?2K^?1 for PZT30/70, 3.00×10^?4 Cm^?2K^?1 for PM01ZT30/70 and 2.40×10^?4 Cm^?2K^?1 for PM03ZT30/70 thin films. The detectivity figures-of-merit (F_D) were 1.07×10^?5 Pa^?0.5 for PZT30/70, 3.07×10^?5 Pa^?0.5 for PM01ZT30/70 and 1.07×10^?5 Pa^?0.5 for PM03ZT30/70. These figures compare well with values reported previously.     

Piezoelectric properties of Li, Sb, and Ta co-doped (K,Na)NbO3 ceramics with fine grain size sintered by SPS method

(Na_0.52?K_0.44Li_0.04)(Nb_0.86Ta_0.06Sb_0.08)O₃ (LTS-KNN) nano-powders with the size of 11–34 nm were prepared by a sol–gel method. Using the nano-powders, LTS-KNN ceramics with fine grain size of 200–400 nm and high density were fabricated by spark plasma sintering. The satisfied piezoelectricity is obtained, such as d ^* ₃₃?~?481 pm/V, d ₃₃?~?296 pC/N, K _p?~?49.7 %, ε ₃₃ ^T /ε ₀?~?920, tanδ?~?0.025 at 1 kHz and relative density is 99.4 %, respectively. It is shown that nano-powders are suitable to prepare fine-grained potassium-sodium niobate ceramics with satisfied properties.     

High-blocking-voltage UMOSFETs with reformed electric field distribution

A high-performance vertical GaN metal–oxide–semiconductor field-effect transistor (MOSFET) with a U-shaped gate (UMOSFET) and high blocking voltage is proposed. The main concept behind this work is to reform the electric field distribution to achieve high blocking voltage. The proposed structure includes p-regions in the drift region, which we call reformed electric field (REF) regions. Simulations using the two-dimensional SILVACO simulator reveal the optimum doping concentration, and width and height of the REF regions to achieve the maximum depletion region at the breakdown voltage in the drift region. Also, the electric field distribution in the REF-UMOSFET is reformed by producing additional peaks, which decreases the common peaks under the gate trench. We discuss herein the impact of the height, width, and doping concentration of the REF regions on the ON-resistance (R_ON) and blocking voltage. The blocking voltage, specific ON-resistance, and figure of merit \( \left( {{\text{FOM}} = \frac{{V_{{{\text{BR}}}}^{2} }}{{R_{{{\text{ON}}}} }}} \right) \) are 1140 V, 0.587 mΩ cm² (V_GS = 15 V, V_DS = 1 V), and 2.214 GW/cm², respectively. The blocking voltage and FOM are increased by about 72 % and 171 % in comparison with a conventional UMOSFET (C-UMOSFET).