Co-Precipitation Method for the Preparation of Nanocrystalline Ferroelectric SrBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> Ceramics

A simple co-precipitation technique had been successfully applied for the preparation of pure ultrafine single phase SrBi₂Nb₂O₉. Ammonium hydroxide and ammonium oxalate were used to precipitate Sr^{2 +}, Bi³⁺ and Nb⁵⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 850C and pure SrBi₂Nb₂O₉ (SBN) phase was formed as revealed by the X-ray diffraction (XRD) studies. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 100. The ferroelectric hysteresis loop parameters of these samples were also studied.     

Nano-sized Pr<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>Co<Subscript>1-x</Subscript>Fe<Subscript>x</Subscript>O<Subscript>3</Subscript> powders prepared by single-step combustion synthesis for solid oxide fuel cell cathodes

Different sets of perovskite-type oxides of general formula Pr_0.8Sr_0.2Co_1-xFe_xO_3-δ (x = 0.0, 0.2, 0.5, 0.8 and 1.0) were successfully prepared by low-cost single-step combustion synthesis at low temperatures based on the auto-ignition reaction of a nitrate solution in the presence of citric acid. Thermogravimetric and differential thermal analysis was carried out on nitrate-citrate precursors to determine the perovskite-phase formation process. The results revealed that the nitrate-citrate precursor exhibited self-propagating combustion behavior. Pr_0.8Sr_0.2Co_1-xFe_xO_3-δ powders showed an orthorhombic single-phase, with their unit cell volume increasing as a function of the Fe content (x). Scanning electron microscopy observations showed that the prepared powders were nanocrystalline. The Pr_0.8Sr_0.2Co_1-xFe_xO_3-δ powders were characterized as fuel cell electrodes on Ce_0.8Sm_0.2O_2-δ pellets in symmetrical cells, and the electrochemical properties of the electrode/electrolyte interfaces were investigated using electrochemical impedance spectroscopy (EIS) as a function of the temperature, Fe content (x) and oxygen partial pressure.     

Dielectric Degradation and Microstructures of Heterogeneous Interfaces in Cofired Multilayer Ceramic Capacitors

The compatibility of electrodes and dielectrics in cofired MLCCs with both Ni and Ag/Pd electrodes was characterized by transmission electron microscopy (TEM) using tripod polished samples. Tripod polishing procedures can reduce entire devices to a thickness of less than 1 m. After low angle ion milling for a short time, many regions across several dielectric and electrode layers are electron transparent, which makes it possible to characterize the cofired interfacial microstructures. When analyzed by convergent beam electron diffraction (CBED) and energy dispersive X-ray spectrometry (EDS), NiO lamellae and P-rich intermediate layers were found in highly accelerated life tested (HALT) MLCCs with Ni electrodes. CBED confirmed that the P-rich layers had a Ba₄Ti₁₃O₃₀ (B₄T₁₃) structures. Oxidized Ni layers containing Mn were also found in the HALT samples. It is believed that Mn ions were reduced by the Ni electrodes, as P-rich and Mn-rich segregated layers were observed in the virginal non-life tested MLCCs. Grains with stacking faults, containing dopants such as Mn, Si, and Mg, had the BaTi₄O₉ (BT₄) structure. No silver diffusion was found in either the BaTiO₃ based perovskite lattices or the flux phases in air-fired X7R type MLCCs.     

Electrochemical Reactions Between Perovskite-Type LaCoO<Subscript>3</Subscript> and Lithium

The perovskite-type composite metal oxide LaCoO₃ was firstly used as an electrode material in rechargeable lithium cells. X-ray diffraction (XRD), scanning electron microscopy (SEM) and extended X-ray absorption fine structure (EXAFS) were employed to analyze the structures of synthesized and discharged LaCoO₃ samples. Cyclic voltammetry and galvanostatic cell cycling were used to characterize the electrochemical performance of LaCoO₃/Li cells. A stable reversible capacity from 110 to 130 mAh/g during up to 50 cycles can be achieved. Based on the analyses of ex-situ XRD and EXAFS of the lithiated/delithiated LaCoO₃ electrode, a three-step electrochemical reaction mechanism was proposed.     

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.     

Surface and morphological investigation of the electrode/electrolyte properties in an all-solid-state battery using a Li<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript> solid electrolyte

All-solid-state lithium-ion batteries represent a promising battery technology thanks to the replacement of the volatile and flammable state-of-the-art liquid electrolyte by a solid electrolyte. Despite the recent progress in the synthesis of sulfide based solid electrolyte with high ionic conductivity, little is known about the interface reactivity of the solid electrolyte with electrode materials. In this study, we synthesized and characterized an amorphous solid electrolyte with the nominal composition (Li₂S)₃(P₂S₅). We assessed the feasibility of using this electrolyte at the laboratory scale, and we discuss the potential challenges that govern its electrochemical performance. Galvanostatic cycling and rate performance measurements were conducted using lithium titanium oxide (Li₄Ti₅O₁₂) as the negative electrode material. The electrochemical measurements were performed using two different counter electrodes, namely Li metal and an InLi_x alloy. The alloy counter electrode suppressed the formation of lithium dendrites, resulting in increased cycling stability and cell safety. Post mortem X-ray photoemission spectroscopy measurements reveal the reactivity of the solid electrolyte Li₃PS₄ with the Li₄Ti₅O₁₂, lithium metal, and InLi_x alloy.     

Crystallization,microstructures and properties of low temperature co-fired CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass-ceramic

CaO-Al₂O₃-SiO₂ glass-ceramic were prepared by melt quenching technique. The crystallization behavior and properties were studied by means of a non-isothermal, thermal analysis technique, X-ray diffraction and scanning electron microscopy. The influence of sintering temperature on phase formation, microstructure, bending strength, dielectric and thermal properties were determined. The activation energy of crystallization and the Avrami parameter were also discussed. The X-ray diffraction results show that SiO₂ phase could be found in all samples and CaSiO₃ and anorthite phases could only be observed in the samples sintered at above 875°C. The densification of glass-ceramic starts at 730°C after the liquid glass is formed and stops at 803°C. Complete densification was achieved at 875°C and the highest mechanical strength was obtained at 850°C, but density significantly decreased at higher temperatures. The coefficient of thermal expansion and the dielectric constant increase with the increasing sintering temperature. The value of the Avrami parameter (n) is ~1.6 and the apparent activation energy (E) is 298 kJ/mol.     

Structure Simulation on Twisted Boundaries in SrTiO<Subscript>3</Subscript> Bicrystals by Molecular Dynamics Calculation

Bicrystals of SrTiO₃ with twisted boundaries were prepared by a HIP method and were observed with a transmission electron microscope (TEM). The bicrystals exhibited different nonlinear current-voltage characteristics depending on twist angle. A Molecular dynamics calculation was applied in order to understand the detailed interface structure. The periodicity of the Σ5 twisted boundary was calculated to be 1.58 times longer than the lattice constant of SrTiO₃ along the (130) axis, and agreed with the periodicity observed by TEM, i.e., 1.57. Coincidence sites formed between Ti ions of the TiO₂ layer and O ions of the SrO layer at the interface and did not shift the positions predicted by a coincidence sites lattice model; such coincidence sites caused the structural periodicity along the interface.     

Raman and infrared spectroscopy of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> - BaTiO<Subscript>3</Subscript> ceramics

Lead-free Na_0.5Bi_0.5TiO₃ -BaTiO₃ ceramics have been prepared in the whole range of concentrations and studied at room-temperature by means of X-ray, Raman scattering and infrared techniques. X-ray measurements revealed rhombohedral, rhombohedral-tetragonal boundaries and tetragonal modifacations depending on the contents of BaTiO₃. The distinct changes of the Raman and infrared spectra with increasing of BaTiO₃ content, which were correlated with X-ray results, were observed. The broad phonon spectra indicated the disorder in the A site of Na_0.5Bi_0.5TiO₃ -BaTiO₃ system.     

The effect of deposition on electrochemical impedance properties of TiO<Subscript>2</Subscript>/FTO photoanodes

The integration of TiO₂ layers onto a substrate is challenging and limits the application potential of TiO₂. Even though, several studies have been reported to solve this problem by applying various deposition methods, there is still lack of information about how these methods affect the electrochemical and photo-electrochemical properties of resulting electrodes. The TiO₂ layers possessing different morphologies, deposited on the conductive FTO glass by means of various different deposition techniques (dip-coating, electrospinning and electrospraying), were used as photoanode (and working electrode) in the three-compartment electrochemical cell. The TiO₂ electrodes were calcinated at 450 °C and after that all samples revealed the crystallographic form of anatase. Using these three deposition techniques, three different morphologies were obtained. They consisted of a thin TiO₂ nanoparticle layer, TiO₂ nanoparticle/nanofiber layer and TiO₂ nanorod layer, respectively. The crystallinity and surface properties of the calcinated layers were determined by XRD, Raman spectroscopy, FTIR-ATR and SEM analyses. The electrochemical impedance (EIS) and photo-induced properties of photoanodes were studied by electrochemical measurements. The effects of surface morphology and crystal size of nanostructured layers on electrochemical impedance and photo-electrochemical properties were investigated. The electrodes prepared by dip-coating technique showed the best electrochemical impedance and photo-electrochemical results compared to other two types of electrodes. Dip-coating TiO₂ layer possesses the biggest crystal size and lowest charge transfer resistance which result the highest photocurrent density.     

Effects of MnO<Subscript>2</Subscript> addition on microstructure and electrical properties of (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>) <Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> ceramics

In this letter, MnO₂-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) lead-free piezoelectric ceramics were synthesized by solid state reaction, and the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction (XRD) reveals that all specimens take on single perovskite type structure, and the diffraction peaks shift to a large angle as the MnO₂ addition increases. Scanning electron microscopy shows that the grain sizes increases, and then decreases with increasing the MnO₂ content. The experiment results indicate that the electrical properties of ceramics are significantly influenced by the MnO₂ content, and the ceramics with homogeneous microstructure and excellent electrical properties are obtained with addition of 0.3 wt% MnO₂ and sintered at 1160°C. The piezoelectric constant (d₃₃), the electromechanical coupling factor (k _p ), the dissipation factor (tan δ) and the dielectric constant (ɛ _r ) reach 160 pC/N, 0.29, 0.026 and 879, respectively. These excellent properties indicate that the MnO₂-doped BNBT-6 ceramics can be used for actuators.     

Dielectric and Ferroelectric Characterization of Na(Ta,Nb)O<Subscript>3</Subscript> Solid Solution Ceramics

Ceramics in the Na(Ta_{1 − x}Nb_x)O₃ system were prepared by a solid state reaction approach, and their dielectric characteristics were evaluated together with the structures. The complete solid solution with orthorhombic structures was observed in the present system, and three supposed phase transitions at about 475, 580 and 650^∘C were observed by DTA. Only one dielectric anomaly was observed at high temperature for x = 0.2 and 0.4, and alternative dielectric anomaly (a diffused dielectric peak) was observed around 170 and 380^∘C for x = 0.6 and 0.8, respectively. The compositions of 0.6 and 0.8 are weakly ferroelectric and those of 0.2 and 0.4 are supposed to be antiferroelectric at room temperature.     

Structural,dielectric and magnetic properties of particulate composites of relaxor (BaTi<Subscript>0.85</Subscript>Sn<Subscript>0.15</Subscript>O<Subscript>3</Subscript>) and ferrite (NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>) synthesized by gel-combustion method

Particulate composites of (1-x) BaTi_0.85Sn_0.15O₃ – x NiFe₂O₄ (with x?=?5, 10,15 and 20 wt%) were synthesized using the solid-state reaction method by sintering at 1350 °C for 4 h. Formation of the diphase composites was confirmed by X-ray diffraction (XRD) and Fourier Transform Infra-red (FTIR) techniques. Temperature (RT-200 °C) and frequency (20 Hz- 1 MHz) dependent of AC conductivity, dielectric constant and dissipation have been studied. The dielectric constant exhibits strong frequency dispersion in the range 20 Hz-1 kHz which is attributed to Maxwell-Wagner interfacial polarization occurring at grain-grain-boundaries interface/interface of grains of BTS-NF. The M-H curve of all the composites exhibited a hysteresis loops typical charcateistic of a ferromagnetic material. The ferromagnetic ordering in the composites on account of NiFe₂O₄ as a constituent is explained using bound magnetic polarons (BMPs) model. The experimental magnetic data have been fitted to BMP model. Value of M_s is smaller, whereas of H_c and M_r are higher of the composites compared to value for NiFe₂O₄. The temperature at which divergence in the M vs. T plot in ZFC and FC starts is higher for the composites than for NiFe₂O₄.     

Phase formations during mechanochemical synthesis of PbTiO<Subscript>3</Subscript>

Lead titanate nanopowders were fabricated by mechanochemical synthesis from lead oxide and titanium dioxide. The milling process has been carefully investigated by X-ray diffraction and X-ray excited photoelectron spectroscopy. The first traces of perovskite phase were detected after 5 h synthesis. It was found that intermediated phases (Ti₁₀O₁₈ and Pb₃O₄) have been formed at the early stage of synthesis. The 50 h milling results in single perovskite phase with average crystallite size of 20 nm.     

Studies of structural,dielectric and impedance properties of Bi<Subscript>9</Subscript>Fe<Subscript>5</Subscript>Ti<Subscript>3</Subscript>O<Subscript>27</Subscript> ceramics

Bi₉Fe₅Ti₃O₂₇ is an eight-layered material belonging to the family of bismuth layered structured ferroelectromagnets. The polycrystalline sample of this compound was prepared by a standard solid-state reaction technique. The formation of the compound in an orthorhombic crystal structure was confirmed by an X-ray diffraction (XRD) technique (lattice parameters: a?=?5.5045[27] Å, b?=?5.6104[27] Å, c?=?76.3727[27] Å). Detailed studies of surface morphology of the compound using scanning electron microscopy (SEM) exhibit that the compound has domains of plate shaped grains. Studies of dielectric and electric properties in a wide temperature range (30–500 °C) at different frequencies (100 Hz–1 MHz) exhibit an anomaly at 291?±?2 °C, which is related to ferroelectric to paraelectric phase transition as suggested by hysteresis loop at room temperature. The values and nature of temperature variation of dc conductivity exhibit the NTCR behavior of the compound.     

Effect of Cr additions on the microstructural stability of Ni electrodes in ultra-thin BaTiO3 multilayer capacitors

Microstructural control in thin-layer multilayer ceramic capacitors (MLCC) is one of the present day challenges to maintain an increase in capacitive volumetric efficiency. This present paper opens a series of investigations aimed to engineer the stability of ultra-thin Ni electrodes in BaTiO₃-based multilayer capacitors using refractory metal additions to Ni. Here, pure Ni and Ni–1 wt.% Cr alloy powders are used to produce 0805-type BME MLCCs with 300 active layers and with dielectric and electrode layer thickness around 1 μm. To investigate the continuity of Ni electrodes, both MLCC chips with pure and doped electrodes were sintered at different temperatures for 5 h. It is found that the continuity of Ni electrodes is improved most likely due to the effect of Cr on the low-melting point (Ni,Ba,Ti) interfacial alloy layer formation. The interfacial alloy layer is not observed when Cr is segregated at Ni-BaTiO₃ interface in the Cr-doped samples, while it is found in all undoped samples. The interfacial alloy layer is believed to increase mass-transfer along the Ni-BaTiO₃ interfaces facilitating an acceleration of Ni electrodes discontinuities.     

Influence of substitution on dielectric diffuseness in Ba<Subscript>(1-x)</Subscript>Bi<Subscript>(2+2x/3)</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics prepared by chemical precursor decomposition method

Barium bismuth niobate, Ba_(1-x)Bi_(2+2x/3)Nb₂O₉ (BBN with x = 0.0, 0.1, 0.2, 0.3, 0.4) ceramic powders in the nanometer range were prepared by chemical precursor decomposition method (CPD). The single phase layered perovskite was prepared throughout the composition range studied. No intermediate phase was found during heat treatment at and above 600°C. The crystallite size and the particle size, obtained from XRD and TEM respectively, were in the range of 15–30 nm. The addition of Bi₂O₃ substantially improved the sinterability associated with high density (96%) which was otherwise difficult in the case of pure BaBi₂Nb₂O₉ (BBN x = 0.0). The sintering was done at 900°C for 4 h. The relative permittivity of BBN ceramics at both room temperature and in the vicinity of the temperature of maximum permittivity (T_m) has increased significantly with increase in bismuth content and loss is also decreased to a certain level of bismuth doping. T_m increased with increase in Bi₂O₃. The diffuseness (γ) in the phase transition was found to increase from 1.54 to 1.98 with the increase in Ba²⁺ substitution level from x = 0.0 to x = 0.3.     

Properties and crystallization kinetics of low temperature co-fired Li<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> electroceramics

The glass-ceramic in the Li₂O-Al₂O₃-SiO₂ system has been prepared by melt quenching route. The crystallization kinetics was studied by differential scanning calorimetry. The effects of sintering temperature on the phase transformation, sintering behavior, bulk density, microstructure, thermal expansion, bending strength and dielectric properties were also investigated by X-ray diffractometry and scanning electron microscopy. (Li, Mg, Zn)_1.7Al₂O₄Si₆O₁₂ is the first crystalline phase forming in the glass-ceramic and transforms to LiAlSi₃O₈ phase at 800 °C. The other two crystalline phases of ZrO₂ and CaMgSi₂O₆ precipitate at 700 and 750 °C, respectively. The densification of this LAS glass-ceramic starts at around 730 °C and stops at about 805 °C. The coefficient of thermal expansion increases with the increasing sintering temperature. The sample sintered at 800 °C for 30 min exhibited excellent properties. The nonisothermal activation energy of crystallization is 149 kJ/mol and the values of Avrami constant (n) are in the range of 3.2 to 3.9. The LAS glass-ceramic sintered at 800 °C for 30 min showed excellent properties. This makes that this material suitable for a number of LTCC applications.     

Dielectric properties of pure and Mn-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics over a wide temperature range

The effect of manganese doping on the dielectric properties of CaCu₃Ti_4-xMn_xO₁₂ (x?=?0, 0.02, 0.04) were investigated over a broad temperature range (93–723 K) in the frequency range from 100 Hz to 10 MHz. Two dielectric relaxations and two dielectric anomalies were observed. The low-temperature relaxation appearing in the temperature range below 200 K is the characteristic relaxation for CaCu₃Ti₄O₁₂. This relaxation was attributed to the polaron relaxation due to electron hopping between Ti³⁺ and Ti⁴⁺ states. Due to the negative factors of notable decreases in the Ti³⁺/Ti⁴⁺ and Cu³⁺/Cu²⁺ ratios and the concentration of oxygen vacancies as revealed by X-ray photoemission spectroscopy, Mn-doping was found to gradually destroy rather than move this relaxation to a higher temperature. The high-temperature relaxation occurring around room temperature was found to be a Maxwell-Wagner relaxation caused by grain boundaries. Our results confirm that the colossal dielectric behavior in the tested samples results from both polaron and Maxwell-Wagner relaxations, but is predominated by the latter relaxation. The low-temperature anomaly behaves as a phase-transition-like behavior. It was argued to be created by oxygen vacancies transition from static disorder to dynamic disorder. The high-temperature anomaly is an artificial effect caused by negative capacitance.     

Characteristics of PZT films with SRO/Pt stack electrodes for high density mbit feram devices

Abstract

Reliable PZT capacitors have been developed by using stable PZT sputtering technique and Pt/thinSRO(SrRuO₃) stack electrodes. Introduction of SRO electrodes with no leakage current degradation is a key to realize reliable and scalable PZT capacitors. Roles of top electrode (TE) SRO and bottom electrode (BE) SRO were investigated respectively from reliability and process damage points of view. The SRO works as hydrogen resistant electrodes, fatigue free interfaces and nucleation sites for perovskite formation. Relationship between SRO crystallinity and PZT electrical properties was elucidated. Templates made of thin SRO were found to function as barrier layers against diffusion of Pb and Ru from BE resulting in new possible cell structures.