Sintering and varistor behaviour of SnO2-Zn2SnO4 composite ceramics

Densified SnO₂-Zn₂SnO₄ composite ceramics were prepared by conventional ceramic processing and the sintering, electrical properties were investigated. The X-ray diffraction results and sintering curves showed that the pellets pressed by ZnO and SnO₂ mixed powders began to shrink after Zn₂SnO₄ was synthesized at about 950 °C. The results suggest that the densification of SnO₂-Zn₂SnO₄ composite ceramics cannot be attributed to the oxygen vacancies created by acceptor doping as traditional viewed. The measurement of J-E curves showed that the SnO₂-Zn₂SnO₄ composite ceramics have good nonlinear properties (α?~?3.9–4.5) without any other doping. Another interesting result is that the composite ceramics have low breakdown electrical field (E _B?~?10 V/mm) with high relative dielectric constant (1 kHz, ε _r?~?6?×?10³). Further studies demonstrate that the varistor behavior is also a grain boundary barrier effect and the barrier height is about 0.84 eV.     

Effect of discharge power density on the properties of Al and F co-doped ZnO thin films prepared at room temperature

ZnO transparent conducting thin films co-doped with aluminium and fluorine (AZO:F) were prepared on glass substrates by RF magnetron sputtering at room temperature. The effect of discharge power density on the microstructure, surface morphology, electrical and optical properties was investigated. From XRD analysis, it was revealed that the intensity of (002) favoured orientation of ZnO films increased with power density from 2.6 to 6.1?W/cm² and then turned to a randomly orientated structure as power density continuously increased to 7.8?W/cm². The film prepared at 6.1?W/cm² showed a better crystallization and microstructure with larger, pyramid-like grains that were approximately 180?nm long and 90?nm wide. As a result, the electrical resistivity of the AZO:F films had a minimum of 4.1?×?10^?4???cm. The improvement in the electrical resistivity of AZO:F films was due to the increase in carrier concentration from 8.8?×?10²⁰ to 1.38?×?10²¹?cm^?3 and the mobility from 5.8 to 11.8?cm² V^?1 s^?1. The increase in carrier concentration with power density was also found to affect the optical property of the films due to the Moss-Burstein shift.     

Structural and electrical properties of Sb-doped p-type ZnO thin films fabricated by RF magnetron sputtering

We investigated the Sb-doping effects on ZnO thin film using RF (radio frequency) magnetron sputtering and RTA (rapid thermal annealing). The structural and electrical properties of the thin films were measured by X-ray diffraction, SEM (scanning electron microscope), and Hall effect measurement. Thin films were deposited at a high temperature of 800°C in order to improve the crystal quality and were annealed for a short time of only 3 min. The structural properties of undoped and Sb-doped films were considerably improved by increasing oxygen content in the Ar-O₂ gas mixture. Sb-doping also significantly decreased the electron concentration, making the films p-type. However, the crystallinity and surface roughness of the films degraded and the mobility decreased while increasing Sb-doping content, likely as a result of the formation of smaller grain size. From this study, we observed the transition to the p-type behavior at 1.5 at.% of Sb. The thin film deposited with this doping level showed a hole concentration of 4.412?×?10¹⁷ cm^?3 and thus is considered applicable to p-type ZnO thin film.     

Ion transport studies on Al–Zn ferrite dispersed nano-composite polymer electrolyte

A ferrite dispersed PEO based nano-composite polymer electrolyte has been developed in the present work. Formation of nano-composites, change in the structural and microscopic properties of the system have been investigated by X-ray diffraction, optical microscopy and SEM imaging. Existence of spinodal decomposition structure indicates formation of nano sized composite polymer electrolyte. Increase in formation of crystalline domain has been evidenced in thermal studies upon dispersal of nano-sized filler particles in pristine electrolyte matrix. The ionic transport studies through impedance spectroscopy exhibit highest electrical conductivity for the composition [93PEO-7NH₄SCN]:2 wt% Al–Zn ferrite, viz. is 1.22?×?10^?4 S/cm at room temperature with ionic transference number in excess of 0.9. Arrhenius type thermally activated conduction process is reflected during temperature dependent conductivity studies on these electrolytes.     

The sintering behavior and microwave dielectric properties of Mg4(Nb,Sb)2O9 ceramics

The sintering behavior, microstructure and microwave dielectric properties of Mg₄(Nb_2?x Sb _x )O₉ (0?≤?x?≤?2) solid solutions were investigated systematically by X-ray diffraction(XRD), scanning electron microscopy(SEM) and a network analyzer. The solid solutions of Mg₄(Nb_2?x Sb _x )O₉ was formed with x value being no more than 1.6. The dielectric constant (?) of the sintered ceramics decreased from 13.06 to 6.28 with Sb content x from 0 to 1.6. With a substitution of Sb⁵⁺ for Nb⁵⁺ (0.04?≤?x?≤?0.08), the sintering temperature of Mg₄Nb₂O₉ ceramics was decreased from 1400 to 1300 °C without degradation of the Qf values. The optimum microwave dielectric properties of ??～?12.26, Qf?～?168,450 GHz, and τ _f?～??56.4 ppm/°C were obtained in the composition of Mg₄(Nb_1.6Sb_0.4)O₉ sintered at 1300 °C.     

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.     

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.     

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.     

Effects of substrate temperature on electrical and optical properties ITO films deposited by r.f. magnetron sputtering

Indium tin oxide (ITO) films have been prepared by r.f. magnetron sputtering using powder target. X-ray diffraction analysis indicates that the deposited films were polycrystalline and retained a cubic bixbite structure. The ITO films deposited at low substrate temperature (T _s) exhibit a (411) preferred orientation but the films deposited at high T _s prefer a (111) orientation. The substrate temperature was found to significantly affect the electrical properties. As the T _s was increased, the conductivity of ITO films was improved due to thermally induced crystallization. The lowest resistivity (8.7?×?10^?4 Ω-cm) was obtained from ITO films deposited at 450 °C. However, optical properties of the films were somewhat deteriorated. The infrared (IR) reflectance of the film increases with increasing the substrate temperature.     

Characteristics of silver powders synthesized from silver 2-ethylhexanoate and Di-n-octylamine

Uniform spherical submicron silver powders were synthesized from a long-chain alkyl carboxylate of silver 2-ethylhexanoate and an alkylamine of di-n-octylamine in this study. The decomposition of silver 2-ethylhexanoate was observed to accelerate significantly in the presence of di-n-octylamine. SEM results revealed that submicron silver powders with sizes ranging from 200 nm to 300 nm and a high tap density of 4.0 g/cm³ were successfully prepared at 150 °C for 3 h in air. TGA reveals that approximately 1.2 wt.% organic residues composed mainly of 2-ethylhexanoate with a slight amount of di-n-octylamine were attached to the silver particles, as confirmed by the FTIR and XPS results. To evaluate the feasibility for practical applications, silver paste prepared from the silver powders synthesized in this study (NAG 80 paste) was examined and characterized, and the results were compared with those of two commercially available powders (SF80 and GH67 pastes). The electrical resistivities of the NAG80 films fired at 300 and 500 °C respectively read 1.8?×?10^?5?Ω-cm and 1.1?×?10^?5?Ω-cm, both superior to those of the SF80 and GH67 films. The fine quality of the uniform submicron spherical silver powders was verified and its potential use in thick film conductors confirmed.     

Electrical conductivities of strontium-doped rare earth ultraphosphates and oxyphosphates

Electrical conductivity of lanthanum ultraphosphate and neodymium oxyphosphate both doped with strontium, La_1-x Sr _x P₅O_14-?? (x?=?0, 0.01, 0.03 and 0.05 in nominal formulae) and (Nd_1-x Sr _x )₃PO_7-?? (x?=?0 and 0.03), respectively, was investigated with a two-probe ac technique. The electrical conductivity was measured as functions of oxygen partial pressure and water vapor pressure in the temperature range of 523 to 673?K for the former and 973 to 1273?K for the latter. La_1-x Sr _x P₅O_14-?? have considerable protonic conductivity, which was evidenced by isotope effect of hydrogen and deuteron on the electrical conductivity, over the wide range of oxygen partial pressure such as oxygen and hydrogen containing atmospheres. La_1-x Sr _x P₅O_14-?? exhibit protonic conductivities of 4.7?×?10^?5?2.2?×?10^?3?S?cm^?1 in the temperature range of 523?C673?K, which is comparable to the other phosphate based protonic conductors. Although protonic defects are considered to be induced and a major positive defect in (Nd_0.97Sr_0.03)₃PO_7-?? , attributed to small protonic mobility, (Nd_0.97Sr_0.03)₃PO_7-?? is a mixed oxide ion and electron hole conductor at 1173?C1273?K, then, it turns to be electron hole conductor below temperatures of 1073?K. (Nd_0.97Sr_0.03)₃PO_7-?? in 1.0?×?10^?2?atm oxygen?C1.9?×?10^?2?atm water vapor had smaller conductivity than that in unhumidified 1.0?×?10^?2?atm oxygen. The conductivities were 9.7?×?10^?3?3.1?×?10^?1?S?cm^?1 and 2.8?×?10^?3?2.5?×?10^?1?S?cm^?1 in the above gases, respectively, in the temperature range of 973?C1273?K. (Nd_0.97Sr_0.03)₃PO_7-?? had larger activation energy such as 165?kJ?mol^?1 than proton conducting La_1-x Sr _x P₅O_14-?? (76?kJ?mol^?1) including other proton conducting phosphates (68?C86?kJ?mol^?1).     

Growth characteristics and film properties of gallium doped zinc oxide prepared by atomic layer deposition

We carried out comprehensive studies on structural, optical, and electrical properties of gallium-doped zinc oxide (Ga:ZnO) films deposited by atomic layer deposition (ALD). The gallium(III) isopropoxide (GTIP) was used as a Ga precursor, which showed pure Ga₂O₃ thin film with high growth rate. Using this precursor, conductive Ga doped ZnO thin film can be successfully deposited. The electrical, structural and optical properties were systematically investigated as functions of the Ga doping contents and deposition temperature. The best carrier concentration and transmittance (7.2?×?10²⁰ cm^?3 and 83.5 %) with low resistivity (≈3.5?×?10^?3?Ωcm) were observed at 5 at.% Ga doping concentration deposited at 250 °C. Also, low correlation of deposition temperature with the carrier concentration and film structure was observed. This can be explained by the almost same atomic radius of Ga and Zn atom.     

Evaluation of La<Subscript>2</Subscript>CoTi<Subscript>0.7</Subscript>Mg<Subscript>0.3</Subscript>O<Subscript>6</Subscript> as an electrode material for a symmetrical SOFC

La₂CoTi_0.7Mg_0.3O₆ (LCTM) material has been prepared at 1473 K for 24 h in air. X-ray powder diffraction study has revealed that it contains two orthorhombic perovskite phases (in a ratio ~1:4) with close unit cell parameters. Annealing of LCTM in reducing (Ar/H₂, 8%) atmosphere at 1173 K for 12 h has resulted in the preparation of a single-phase material containing the GdFeO₃-type perovskite phase with the unit cell parameters of a?=?5.5631(3) Å, b?=?5.5462(3) Å, c?=?7.8522(5) Å. LCTM material exhibits a reversible transformation of a mixture of two perovskite phases with close cation content in air and a single perovskite phase in a reducing atmosphere. Both as-prepared and reduced LCTM samples have been studied by thermogravimetric analysis and dilatometry in air and Ar/H₂ (8%). No chemical interaction between the as-prepared LCTM and standard electrolyte materials for SOFC like GDC and YSZ has been observed up to 1273 K. High-temperature electrical conductivity of the as-prepared LCTM at variable oxygen partial pressure (10^?4-0.21 atm) showed weak dependence over pO₂ with E_a?=?0.48?±?0.01 eV. AC impedance study of the symmetrical cells LCTM/GDC/LCTM has revealed ASR value at 1173 K of ~8.1?±?0.1 Ω?cm² in air and 0.24?±?0.05 Ω?cm² in a reducing atmosphere. These results allow to consider LCTM as a promising electrode material for a symmetrical SOFC.     

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.     

Electrical and optical properties of fluorine-doped tin oxide (SnOx:F) thin films deposited on PET by using ECR–MOCVD

The electrical, optical, structural and chemical bonding properties of fluorine-doped tin oxide (SnO_x:F) films deposited on a plastic substrate prepared by Electron Cyclotron Resonance–Metal Organic Chemical Vapor Deposition (ECR–MOCVD) were investigated with special attention to the process parameters such as the H₂/TMT mole ratio, deposition time and amount of fluorine-doping. The four point probe method, UV visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic emission spectroscopy (AES), X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the films. Based on our experimental results, the characteristics of the SnO_x:F thin films were significantly affected by the process parameters mentioned above. The amount of fluorine doping was found to be one of the major parameters affecting the surface resistivity, however its excess doping into SnO₂ lead to a sharp increase in the surface resistivity. The average transmittance decreased with increasing film thickness. The lowest electrical resistivity of 5.0?×?10^?3 Ω^.cm and highest optical transmittance of 90% in the visible wavelength range from 380 to700 nm were observed at an H₂/TMT mole ratio of 1.25, fluorine-doping amount of 1.3 wt.%, and deposition time of 30 min. From the XRD analysis, we found that the SnO_x:F films were oriented along the (2 1 1) plane with a tetragonal and polycrystalline structure having the lattice constants, a?=?0.4749 and c?=?0.3198 nm.     

Pyroelectric, dielectric, and piezoelectric properties of MnO2-doped (Na0.82 K0.18)0.5Bi0.5TiO3 lead-free ceramics

MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ lead-free piezoelectric ceramics were prepared by conventional solid-state reaction process and the effect of MnO₂ addition on the pyroelectric, piezoelectric and dielectric properties were studied. The experiment results showed that the pyroelectric, piezoelectric, and dielectric properties strongly depended on MnO₂ addition in the (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramics. Excellent electrical properties were obtained in (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ with 0.8?mol% MnO₂. The large dielectric loss of pure BNT ceramics was significantly reduced, the piezoelectric constant was improved, and it also showed excellent pyroelectric properties when compared with other lead free ceramics, with pyroelectric coefficient p?=?17?×?10^?4?C/m²K and figure of merit F _d ?=?6.56?×?10^?5?Pa^?0.5. With these outstanding pyroelectric properties, the 0.8?mol% MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramic can be a promising material for pyroelectric sensor applications in future.     

Effect of Zn2SnO4 on the sintering and electrical properties of SnO2 ceramics

SnO₂ ceramics with relative density about 98 % were obtained based on the addition of Zn₂SnO₄. The shrinkage of the ceramic samples increased sharply and got a saturated value about 13.3 % with doping more than 0.2 mol% Zn₂SnO₄. In the dielectric spectra, no relaxation peaks were observed and no deep trap states could be detected from 50–300 °C and 40–5 M?Hz. Thus, the oxygen vacancies may not be necessary for the densification of SnO₂ ceramics during sintering process. For all the samples, nonlinear electrical properties were observed and the breakdown electrical fields are in good agreement with the barrier height. With increasing Zn₂SnO₄ content, the activation energies E _a for O^? or O^2? adsorbed at grain boundary decreased and the doping of Zn₂SnO₄ may be an important reason for the improve of grain conductivity and formation of Schottky barrier.     

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.     

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.     

Synthesis and dielectric properties of Ba2TiSi2O8 glass-ceramics from the sol–gel process

The Ba₂TiSi₂O₈ glass-ceramics were prepared by sol–gel process using barium acetate, titanium butoxide, tetraethoxyorthosilicate and boric acid as raw materials. Because of the existence of glass and sintering additive, the Ba₂TiSi₂O₈ glass-ceramics can be sintered at 880 °C in air. The structure of sintered sample was characterized by means of XRD and SEM. XRD patterns showed that fresnoite Ba₂TiSi₂O₈ is the dominant crystalline phase in the sintered samples. SEM images indicated that the shape of Ba₂TiSi₂O₈ grains varied with the molar ratio of ([Ba(Ac)₂/Ti(OBuⁿ)₄/Si(OEt)₄]). With an increase of Si(OEt)₄ content, the length/diameter ratio of Ba₂TiSi₂O₈ grains decreases. The Ba₂TiSi₂O₈ glass-ceramics studied in this work have ?_r in the range of 6–12 (100 MHz) and demonstrate very low dielectric losses (tanδ <2?×?10^?3, 100 MHz). The experimental results suggested that the Ba₂TiSi₂O₈ glass-ceramics could be used as dielectric materials for low temperature co-fired ceramics (LTCC) process.