Silicon oxycarbides can be considered as being carbon‐containing silicates consisting of glass networks in which oxygen and carbon share bonds with silicon. The carbon‐for‐oxygen substitution in ...silicate glass networks has been shown to induce significant changes in the network connectivity and consequently strong improvements in the properties of the silicate glass network. For instance, SiOC glasses exhibit Young's moduli, hardness values, glass transition, and crystallization temperatures which are superior to those of vitreous silica. Moreover, the silicon oxycarbide glass network exhibits unique structural features such as reduced mass fractal dimension and nano‐heterogeneity, which significantly affect and/or dictate its properties and behavior. In the present Review, a consideration of the current state of the art concerning the synthesis, processing, and various structural and functional properties of silicon‐oxycarbide‐based glasses and glass‐ceramics is done. Thus, the synthesis of silicon oxycarbides starting from macromolecular precursors such as polysiloxanes or alkoxysilanes‐based sol‐gel systems as well as current advances related to their processing will be critically reviewed. In addition, various structural and functional properties of silicon oxycarbides are presented. Specific emphasis will be put on the intimate correlation between the molecular architecture of the precursors and the structural features and properties of the resulting silicon oxycarbides.
In the present Review, a consideration of the current state of the art concerning the synthesis, processing as well as various structural and functional properties of silicon‐oxycarbide‐based materials is done.
The culture of Zen comes into two diverse paths in China and Japan. Compared to China, the Japanese Zen culture has characteristics of natural, plain, sensitive, vanity and silence. It is ...unrestrained with feeble and desolation. And these characteristics are presented in Japanese domestic ceramic in the unique beauty of its domestic ceramic.
Ferroelectric perovskites such as BaTiO3 and Pb(Zr,Ti)O3 are well-suited for a variety of applications including piezoelectric transducers and actuators, multilayer ceramic capacitors, thermistors ...with positive temperature coefficient, ultrasonic and electro-optical devices. Ferroelectricity arises from the long-range ordering of elemental dipoles which determines the appearance of a macroscopic polarization and a spontaneous lattice strain. The confinement of a ferroelectric system in a small volume produces a perturbation of the polar order because of the high fraction of surface atoms and ferroelectricity vanishes when the size of the material is reduced below a critical dimension. This critical size is of a few nanometres in the case of epitaxial thin films and of 10−20 nm for nanoparticles and nanoceramics. The change in properties with decreasing physical dimensions is usually referred to as size effect. Thin films and ceramics are particularly prone to show size effects. A progressive variation of dielectric, elastic and piezoelectric properties of ferroelectric ceramics is already observed when the grain size is reduced below ≈10 μm, i.e. at a length scale much larger than the critical size. In this case it is more appropriate to refer to scaling effects as they are not related to material confinement.
The aim of this contribution is to review the current understanding of size and scaling effects in perovskite ferroelectric ceramics and, in particular, in BaTiO3. After a short survey on the intrinsic limits of ferroelectricity and on the impact of particle/grain size on phase transitions, the role of interfaces such as ferroelectric/ferroelastic domain walls and grain boundaries in scaling of dielectric and piezoelectric properties will be discussed in detail. Multiple mechanisms combine to produce the observed scaling effects and the maximization of the dielectric constant and piezoelectric properties exhibited by BaTiO3 ceramics for an intermediate grain size of ≈1 μm. The broad dispersion of experimental data is determined by spurious effects related to synthesis, processing and variation of Ba/Ti ratio. Furthermore, we will consider these size effects, and other properties in relation to the downsizing the modern multilayer BaTiO3 based capacitors.
Normal sintering of Li‐doped and Li/Ta‐codoped potassium sodium niobate (KNbO3–NaNbO3, KNN)‐based ceramics was investigated to clarify the optimal sintering condition for densification, ...microstructure, and electrical properties. It was found that density increased greatly within a narrow temperature range but tended to decrease when the sintering temperature slightly exceeded the optimal one, accompanied by the appearance of abnormal grain growth, which was considered to be due to the intensified volatilization of alkali metal oxides. Piezoelectric and dielectric properties also showed a similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density, because both densification and composition affect the electrical properties. The highest d33 value of 206 pC/N was obtained for the Li‐ and Ta‐codoped KNN ceramics prepared at 1090°C.
Lead‐free piezoelectric ceramics have received attention because of increasing interest in environmental protection. Niobate ceramics such as NaNbO3 and KNbO3 have been studied as promising Pb‐free ...piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, highly dense Na0.5K0.5NbO3 ceramics were prepared using spark plasma sintering (SPS). Although the SPS temperature was as low as 920°C, the density of the Na0.5K0.5NbO3 solid solution ceramics was raised to 4.47 g/cm3 (>99% of the theoretical density). After post‐annealing in air, reasonably good ferroelectric and piezoelectric properties were obtained in the Na0.5K0.5NbO3 ceramics with submicron grains. The crystal phase of the Na0.5K0.5NbO3 has an orthorhombic structure. The Curie temperature is 395°C and the piezoelectric parameter (d33) of the Na0.5K0.5NbO3 ceramics reached 148 pC/N.
We present a novel processing route to synthesize homogeneous ceramic polymer composites with ultrahigh (a1478 vol.%) packing density by using the spouted bed granulation technology and subsequent ...warm pressing. In the granulation process, two ceramic particle size fractions (I--Al2O3) and a thermoplastic polymer (polyvinyl butyral) are assembled to granules. In the process, mu m-sized particles are coated with a layer of polymer which contains a second, nm-sized ceramic particles fraction. The mass fractions of each constituents can be adjusted independently. During the warm pressing, the nm-sized particle fraction along with polymer is pressed into the void volume of the mu m-sized particles, thus achieving a homogeneous, isotropic composite structure with a very high packing density of ceramic particles. The material, which can easily be produced in large quantities, combines a high modulus of elasticity (up to 69 GPa), tensile strength (a1450 MPa), and pronounced fracture strain (a140.1%) with an isotropic, biocompatible, metal-free composition. Possible failure mechanisms are discussed, including failure due to necking of the polymer, and failure due to limited polymeraparticle-interfacial strength.
(Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy ceramics (HEC) with a submicron grain size of 400 to 600 nm were fabricated by spark plasma sintering using a two‐step sintering process. Both X‐ray and ...neutron diffractions confirmed the formation of single‐phase with rock salt structure in the as‐fabricated (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C samples. The effect of submicron grain size on the thermal stability and mechanical properties of HEC was investigated. The grain growth kinetics in the fine‐grained HEC was small at 1300 and 1600°C, suggesting high thermal stability that was possibly related to the compositional complexity and sluggish diffusion in HEC. Compared to the coarse‐grain HEC with a grain size of 16.5 µm, the bending strength and fracture toughness of fine‐grained HEC were 25% and 20% higher respectively. The improvement of mechanical properties in fine‐grained HEC may be attributed to micromechanistic mechanisms such as crack deflection.
Bioactive and inert dental glass‐ceramics Montazerian, Maziar; Zanotto, Edgar Dutra
Journal of biomedical materials research. Part A,
February 2017, Volume:
105, Issue:
2
Journal Article
The study on novel physical properties of structural ceramics or ceramic composites could make them more conducive to be function‐ and structure‐integrated materials. Herein, titanium nitride‐alumina ...(TiN–Al2O3) duplex ceramics were prepared and the dielectric spectra of the ceramics were studied from 10 MHz to 1 GHz. Negative permittivity appeared when TiN content exceeded 40 wt% due to the induced plasmonic state of massive delocalized electrons in connected TiN grain networks. Meanwhile, alternating current conduction behaviors of the duplex ceramics were discussed with percolation theory. Furthermore, the analysis of reactance by equivalent circuit models indicated that negative permittivity ceramics exhibited inductive character. This work realized negative dielectric behaviors in TiN–Al2O3 duplex ceramics and would promote the study of electromagnetic functionalization in wave shielding or attenuation for structural ceramics.
Bioceramics: Past, present and for the future Best, S.M.; Porter, A.E.; Thian, E.S. ...
Journal of the European Ceramic Society,
2008, 2008-1-00, 20080101, Volume:
28, Issue:
7
Journal Article, Conference Proceeding
Peer reviewed
There have been a number of major advances made in the field of bioactive ceramics, glasses and glass ceramics during the past 30–40 years. From initial work on the development of materials that are ...tolerated in the physiological environment, emphasis has now shifted towards the use of ceramic materials that interact with bone tissue by forming a direct bond. It is now possible to choose, by compositional control, whether these materials are biologically stable once incorporated within the skeletal structure or whether they are resorbed over time. This paper reviews the ground-breaking work that was performed during the 1970s and 1980s in the field of bioceramics in the production and characterisation of bioactive and bioresorbable glasses, glass ceramics and calcium phosphates. The review then explores the influence of the original concepts and ideas on the more recent development of ceramic scaffolds, composites and coatings with enhanced bioactivity for bone tissue engineering.
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