Electronic Ceramics Research Articles

Structural, thermal expansion and heat capacity study of lead-free [(1 − x)(Na0.5Bi0.5)–xBa]Zr1−y Ti y O3 ceramics

Lead-free ceramics of Na0.5Bi0.5TiO3–Ba(Ti,Zr)O3 (NBT–BTZ) were prepared by solid phase hot pressing sintering process. The obtained samples show perovskite structure. Structural, the heat capacity, thermal expansion and pyroelectric measurements were made in wide temperature range. The broad anomalies of heat capacity and thermal expansion were observed, which approximately correspond to structural, pyroelectric and dielectric properties. It was concluded that these anomalies can be connected with temperature features of polar regions and with formation of long-range ferroelectric state. The obtained results are discussed in the framework of foreign ions/lattice imperfections, which create local electric and elastic fields. The NBT–BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.

Investigation of the additive induced doping effects in gelcast soft lead zirconate titanate ceramics

Due to the high sensitivity of the electrical properties of electronic ceramics to various factors, knowledge about the possible influence of the processing procedure on their electrical performance is critical for applying a new technique to the fabrication of the materials. In this study, various electrical parameters, complex impedance spectra, ferroelectric hysteresis loops, and microstructures of soft lead zirconate titanate (PZT) ceramics formed by the gelcasting technique from suspensions with various dispersants were investigated in comparison with those of the conventional dry pressed ones. We found that the sodium ion, which is the main cation in many commercial surfactants, exhibited obvious hard doping effects; thus causing deteriorated performance of the gelcast PZT ceramics. While a certain impurity ion introduced by a dispersant was also found to induce soft doping characteristics and improve the electrical performance of the materials. The results suggest that the doping effects of the metal ions or impurities introduced by the dispersants, or other additives, should be generally considered for applying a wet processing technique to forming multicomponent electronic ceramics.

Transmission electron microscopy of electronic ceramics

Transmission electron microscopy of electronic ceramics

International Seminar on Science and Technology of Glass Materials (ISSTGM-2009)

The progress of the human race is linked with the development of new materials and also the values they acquired in the course of time. Though the art of glass forming has been known from Egyptian civilization, the understanding and use of these glasses for technological applications only became possible once the structural aspects were revealed by the inspiring theories proposed by William H Zachariasen. Glass and glass ceramics have become the essential materials for modern technology. The applications of these materials are wide and cover areas such as optical communication, laser host, innovative architecture, bio-medical, automobile and space technology. As we master the technology, we must also learn to use it judiciously and for the overall development of all in this global village.The International Seminar on Science and Technology of Glass Materials (ISSTGM-2009) is organized to bring together scientists, academia and industry in order to discuss various aspects of the technology and to inspire young scholars to take up fruitful research. Various topics such as glass formation and glass-ceramics, glass structure, applications of glass and glass ceramics in nuclear waste management, radiation dosimetry, electronics and information technology, biotechnological applications, bulk metallic glasses, glasses containing nano-particles, hybrid glasses, novel glasses and applications in photonics, Non-linear optics and energy generation were discussed.In this volume, 59 research articles covering 18 invited talks, 10 oral presentations and 31 poster presentations are included. We hope these will serve as a valuable resource to all the scientists and scholars working with glass materials.Acharya Nagarjuna University, established in 1976, is named after the great Buddhist preceptor and philosopher, Acharya Nagarjuna, who founded a university on the banks of river Krishna some centuries ago. The University is situated between Vijayawada and Guntur, the famous commercial and academic centers of Andhra Pradesh, India. The Departments of Physics of Acharya Nagarjuna University and the Nuzvid Campus have existed since the inception of the University. For the past decade and a half, these Departments have been actively involved in research on glass materials. More than 200 research articles have been published by staff members of these departments exclusively on glass materials. A number of Major Research Projects are being carried out by the staff members of these Departments. The organizing committee is indebted to all the scientists and scholars for their active participation in the seminar and their contribution to this proceedings. The committee expresses its gratitude to the authorities of Acharya Nagarjuna University (The Vice-Chancellor, The Rector and The Registrar), Department of Atomic Energy, Board of Research in Nuclear Sciences, Department of Science and Technology, Council of Scientific and Industrial Research, Defence Research and Development Organization and AP State Council of Science and Technology for their financial support. The committee thanks the IOP: Conference Series publisher for publishing this proceedings which added value to the seminar. Professor N Veeraiah Convener and Editor-in-Chief Professor D Krishna Rao Co-Convener

Electrical Transport in Lead-Free [(1−x)(Na0.5Bi0.5)-xBa]Zr1 - yTiyO3 Ceramics (x = 0, 0.06, and y = 0, 0.96)

Lead-free ceramics based on (Na 0.5 Bi 0.5 TiO 3 , NBT)-(Ba(Ti,Zr)O 3 , BTZ) were prepared by solid phase hot pressing sintering process and their ac (σ ac ) and dc (σ dc ) conductivity have been studied (303–753 K). Low frequency (100 Hz–100 kHz) ac conductivity obeys power law σ ac ∼ ω s characteristic for disordered materials. The frequency exponent s is a decreasing function of temperature and tends to zero at high temperatures. Dc conductivity has thermally activated character and possesses four linear parts with four different activation energies and some discontinous changes. However, σ ac (T) possesses two linear parts with two different activation energies and more discontinuous changes than dc conductivity. The results was interpreted by correlated hopping model. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.

Preparation and electrical properties of xCaRuO 3/(1 − x)CaTiO 3 perovskite composites

CaRuO 3–CaTiO 3 ceramic composites were prepared by sintering for short times for potential applications in the areas of electronic ceramics. Scanning electron microscopy and energy dispersive X-ray analysis showed two separate phases, CaRuO 3 and CaTiO 3 in the composite. Conductivity data, measured by the four-probe method, showed that the composites have high electrical conductivity when x ≥ 0.19 in xCaRuO 3–(1 − x)CaTiO 3 composites. Furthermore, the nanoparticle of calcium ruthenate prepared by reverse micelle synthesis was used to be conductive agent for the composite. The result shows that the use of nano-sized calcium ruthenate enabled higher electrical conductivity to be maintained down to x = 0.09.

Study on nanosized zircon powder based dual sensitive sensor

Study on the nanosized ceramic material of ZrO 2 which has usually been used as electronic ceramics, function ceramics, structure ceramics and so on. The material of ZrO 2 was made by low-temperature super alkaline condition. The powder was detected by XRD, and the result showed that the material was pure ZrO 2. According to the Scherer formula computation, the ZrO 2 average grain diameter was about 21 nm. The material was sensitive both to the ammonia and to the humidity. Full performance test was carried to the sensor made by the sensitive material. To 20 × 10 −6 NH 3, the sensitive is 3, and to 1000 × 10 −6 NH 3, the sensitive is 12.5. The sensor has good selectivity, and has almost no sensitive to else gases, so it is a good gas sensor with excellent selectivity. To 1000 × 10 −6 NH 3, the response time is 2 s, and recovering time is also only 27 s. The sensitive range of humidity is 25–98%RH under 25 °C. Both response and recovered time of humidity are less than 30s. The sensor realized the dual sensitive.

Development of Pd-coated ceramic electrodes in hybrid sulphur cycle

The Hybrid Sulphur (HyS) cycle has attracted much attention as a mass production process for hydrogen. It consists of an electrolysis step and a thermal decomposition one. In order to achieve high efficiency for hydrogen production and operational cost reduction, some developments in electrode materials with high corrosion resistance, high electrical conductivity and low anodic potential is a key issue for the electrolysis in H2SO4 solution.Our research group pointed out that some electronic conductive ceramics, which are titanium (Ti)-based pyrochlores (chemical formula: A3+2Ti4+2O7) and perovskites (chemical formula: A2+Ti4+O3), might be some of the candidates for anode base materials. We developed the sintering process of electronic conductive ceramics which had high corrosion resistance and high electrical conductivity. In this paper, our research activities for the development of a new type of anode material are introduced, i.e., the material development of electronic conductive ceramics, corrosion resistance evaluation and electrical conductivity evaluation of Ti-based ceramics in a 50 weight(wt.)% H2SO4 solution at the operating temperature are summarised. Additionally, the application of a palladium (Pd)-coating technique on the titanate was evaluated using the electroless deposition technique, in order to provide some catalytic properties to the materials.

レーザー援用エアロゾルデポジション法による基材の熱ダメージを抑えた電子セラミックス厚膜の熱処理プロセス

Laser annealing has been conventionally used for surface treatment, sintering of structural materials and crystallization of amorphous materials. This article describes the possibility to apply laser annealing for electronic ceramics. Pb(Zr, Ti)O3 (PZT) films with a thickness of over 10 μm directly deposited onto stainless-steel substrates (PZT/SUS) by aerosol deposition (AD) technique have been annealed by infrared laser irradiation in order to improve their ferroelectric and/or piezoelectric properties. The metallic luster of the stainless-steel substrate has been retained after laser heating. The remanent polarization (Pr) and coercive field (Ec) values of the films annealed by laser irradiation was Pr > 40 μC/cm2 and Ec < 40 kV/cm, respectively, being superior to those of the PZT/SUS annealed by electric furnace. The area of grain growth for the irradiated PZT films coincides with the fascicle spot size. In contrast, in the case of bulk PZT, infrared laser irradiation with the same spot size is causing grain growth on a larger area (20 times the spot diameter). The combination of laser annealing and AD technique is attractive not only for production of electronic ceramics devices but also to confirm to heat treatment of electronic ceramics to the desired areas.

Oxygen permeation and microstructure of intergrowth perovskite Sr-La-Fe-Co based mixed-conductive ceramics

The partial oxidation reforming method is advantageous to develop highly effective and low-cost products of H2 gas used for fuel cells. For the partial oxidation, however, large amount of pure O2 gas are desirable for acceleration of the H2 production. Electronic and oxygen ionic conductive (mixed-conductive) oxide ceramics can be used to obtain pure O2 gas, because the mixed conductivity contributes to permeate pure O2 gas from air at the elevated temperatures. However, high permeation temperature of above 900°C is a problem. Higher temperature for the permeation incurs deterioration of both the ceramics and the steel to support the ceramics. We intend to find out a new mixed-conductive oxide with high oxygen permeation at lower temperatures than 900°C. In this study, we focus the Sr-La-Fe-Co oxides characterized by the intergrowth structures. We have investigated an appropriate condition to prepare Sr3-xLaxFeCoO7-δ ceramics with intergrowth perovskite structure. Then we have investigated microstructures as well as oxygen permeation properties of a dense Sr2.45La0.55FeCoO7-δ ceramics. The oxygen permeation flux of the Sr2.45La0.55FeCoO7-δ ceramics was as high as that of cubic perovskite Sr0.8La0.2 Fe0.8Ga0.2O3-δceramics.

Synthesis and characterization of the NiAl 2O 4, CoAl 2O 4 and ZnAl 2O 4 spinels by the polymeric precursors method

The spinels constitute an important group of materials with great technological appeal, being able to be applied as pigments, refractory, catalysts and electronic ceramics. In this paper, we reported the preparation of nanocrystalline NiAl 2O 4, CoAl 2O 4 and ZnAl 2O 4 phases by Pechini method. This method employs the dissolution of cations precursors in a citric acid aqueous solution. Due to the high chemical homogeneity, cation segregation during thermal decomposition is minimal. The resulting powders were characterized by XRD, N 2 adsorption/desorption curves (BET curves) and SEM. The X-ray diffraction patterns show that the synthesis is efficient to produce single-phased NiAl 2O 4, CoAl 2O 4 and ZnAl 2O 4 powders and the crystallite sizes were 12, 34 and 20 nm, respectively. The micrographs show the formation of soft agglomerates with irregular morphology constituted by the superposition of the quite fine particles.

DIELECTRIC PROPERTIES OF LEAD-FREE [(1-x)(Na0.5Bi0.5)-xBa]Zr1−y Ti y O3 CERAMICS (x = 0.01, 0.06, 0.085, 0.09, 0.1 AND y = 0.96, 0.97)

ABSTRACT Lead-free ceramics based on (Na0.5Bi0.5TiO3, NBT)-(Ba(Ti, Zr)O3, BTZ) were prepared by solid phase synthesis and hot pressing sintering process and their dielectric properties have been studied. The obtained results were compared with these for pure NBT. The obtained samples show pure perovskite structure. Low frequency (100 Hz-100 kHz) investigations reveal the diffuse phase transitions and relaxorlike behaviour. The obtained results are discussed in terms of inhomogeneity of ions distribution, their ferro- and antiferroactivity and internal stresses. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.

Micro- and Nano-patterning of Solution-Derived Functional Electronic Ceramics

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Microstructure and properties of ceramics and composites joined by plastic deformation

A review is presented of the design of suitable materials systems for joining by high-temperature plastic deformation, details of the joining techniques, microstructures and properties of the resulting composite bodies, and prospects and limitation for this type of joining technology. Joining parameters and resulting forms are discussed for Al 2O 3/mullite particulate composites, Y 2O 3-stabilized ZrO 2 particulate/Al 2O 3 particulate and whisker-reinforced composites, hydroxyapatite bioceramics, La 0.85Sr 0.15MnO 3 electronic ceramics, MgF 2 optical ceramics, and Ni 3Al intermetallics. Results are contrasted with those obtained by other methods of joining brittle, high-temperature materials, with special focus on durability and mechanical properties.

Formation of controlled alumina films using Supercritical Fluids Chemical Deposition for electronic and telecommunication devices

ABSTRACTAlumina is one of the most widely used oxide ceramic material. It exists in many metastable forms, among which is the thermodynamically stable α phase, obtained upon severe thermal treatment. Sintering of alumina is generally performed in several stages: first, phase transitions towards the stable α phase followed by its densification. The first step is strongly dependent on the crystallinity of initial powders. By controlling this parameter, it is possible to optimize the sintering properties, in particular by decreasing the phase transition temperature. This effect has been studied for alumina elaborated in sub- and supercritical fluid media. This work highlights the possibilities to obtain, according to the nature of the fluid, different kinds of transition alumina: boehmite AlO(OH) or amorphous Al2O3. The sintering processes of these powders all lead to α-alumina, however, different microstructures and densities can be obtained. A significant shift towards lower λ/α phase transition temperature is also observed when amorphous alumina is considered, compared to boehmite. The transfer of this know-how to the design of core-shell nanoparticles and film deposition onto copper heat sinks is investigated to develop nanostructured ceramics for telecommunications and electronics.

Effects of Ag-Pd Powder on Ferroelectric and Mechanical Properties of PLZT Ceramics

The Ag-Pd/PLZT composites were prepared by the conventional electronic ceramics method. The electrical and mechanical properties of the composites were investigated. As the amount of doped Ag-Pd particles increased, the fatigue and mechanical properties of the composites were improved, and the dielectric and ferroelectric properties after electric fatigue dropped less. The results indicate that the fatigue process leaves less damage on the composites due to the Ag-Pd particles incorporation. It is proposed that the improvement of fatigue property may be attributed mainly to the improvement of mechanical property.

Low sintering BaNd 2Ti 4O 12 microwave ceramics prepared by CuO thin layer coated powder

Recently, BaO–Nd 2O 3–TiO 2 systems are widely studied for microwave applications because of their high dielectric constant and high quality factor. However, pure BaNd 2Ti 4O 12 ceramics without additives have to be sintered above 1300 °C to achieve densification. Copper oxide has been known as a good sintering aid for electronic ceramics and less reactive toward silver. We have introduced the CuO into BaNd 2Ti 4O 12 by modifying the surface of BaNd 2Ti 4O 12 by CuO thin layer on the calcined powder instead of mixing CuO directly with BaNd 2Ti 4O 12 powder. The process reduces the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties such as quality factor. The CuO precursor solution of Cu(CH 3COO) 2, Cu(NO 3) 2 and CuSO 4, were used to prepare CuO thin layer. They were investigated individually to determine their effects on the densification, crystalline structure, microstructure and microwave dielectric properties of BaNd 2Ti 4O 12. The CuSO 4 coated BaNd 2Ti 4O 12 sintered at 1150 °C has exhibited better dielectric properties than those of CuO doped BaNd 2Ti 4O 12 ( k, 62.5 versus 61.2; Q × f, 11,500 GHz versus 10,500 GHz). The thin layer dopant coating process has been found to be a very effective way to lower ceramic sintering temperature without scarifying its dielectric properties.

Theoretical Aspects of PTC Thermistors

The discovery of ferroelectric barium titanate (BaTiO₃) in 1942 began the present era of dielectrics-based electronic ceramics. Ferroelectric barium titanate has a high dielectric constant and after the recognition of BaTiO₃ as a new ferroelectric compound, various attractive electrical properties have been extensively studied and reported. Since then, pioneering work on valence-compensated semiconduction led to the discovery of the positive temperature coefficient (PTC) of the resistance effect found in doped BaTiO₃. Significant progress has since followed with respect to understanding the PTC phenomena, advancing materials capabilities, and developing devices for sensor and switching applications. In this paper, the theoretical aspects of the various PTC models are discussed and the future trends of practical applications for PTC devices are briefly mentioned.

Low-temperature-sintering and characterization of glass-ceramic composites

To meet the demands of high power and high-speed propagation of the signal for very large scale integration, a series of glass/ceramic composites were prepared using electronic ceramics process from borosilicate glass with Sr-celsian, which contains 30, 40, 50, 60, 70 wt% ceramic. The phase and microstructural evolution of the composites were characterized by XRD and SEM. The properties of the composites were also measured. Results show that the thermal expansion coefficient, dielectric constant and hardness of the composites increase with an increase content of Sr-celsian. However, the dielectric loss decreases with increasing Sr-celsian content. For the composites with ≧ 60 wt% Sr-celsian fired at 850–900°C, formation of α-quartz and cristobalite in the composites during the sintering process has bad effect on thermal expansion, but has little effect on the values of dielectric properties of the composites. The obtained composites exhibit low dielectric constant (5.2–5.8), low dielectric loss (⩽ 0.25%), low thermal expansion coefficient (4.4–6.2 × 10−6°C−1) and low-temperature sintering behavior (⩽900 °C), which suit for electronic packaging field.

Electronic ceramics based on polycrystalline SnO2, TiO2 and (Sn xTi1-x)O2 solid solution

In the present text we discuss on electronic properties arising from polycrystalline semiconductor ceramics of SnO2, TiO2 and (Sn xTi1-x)O2 solid solution rutile-type structure. This is intended to be a short overview of the most recent papers in this area. One of the most important content discussed in this text is based on sinterability of these polycrystalline ceramics, which depends on the target application used to project porous or highly dense microstructure. The majority of discussion is focused in two main applications: varistor and sensor. In both applications there are similarities involved in the control of the sensor and varistor properties, which can mainly ascribed to the grain boundary structure and composition. The similarities found are consistently explained by the fact that all of these n-type semicondutor ceramics have the tendency to establish a grain boundary region with a "p-type semiconductor nature" (due to metal transition atoms segregated at the grain boundary region and then favors negative charged species to adsorb and enrich this region). This configuration enables electrons to become localized on the surfaces, giving rise to a negative surface and, as a result, electron depletion layers are formed, acting as potential barriers which control the properties of the mentioned devices.