Electroceramic oxides

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

In lead zirconate, PbZr03, the larger lead ions are displaced alternately from the cube comer sites to produce an antiferroelectric. This can readily be converted to a ferroelectric by the substitution of Ti4+ ions for some of the Zr4+ ions, the maximum value of permittivity occurring at about the 50 50 mixture of PbZrC 3 and PbTiC 3. The resulting PZT ceramics are used in a number of capacitance and electro-optic applications. The major problem in the preparation of these solid solutions is the volatility of PbO. This is overcome by 

The fact that the site occupation in magnetite is opposite to that of spinel arises from the interaction of the d electrons on the cations with the surrounding anions. The energy for the exchange 

Results of quantum-mechanical calculations (Dunitz and Orgel, 1957) have given values for the OSPEs of a number of transitional metal ions and the degree of inversion of mixed spinels 

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Jones AC (2002) Molecular design of improved precimsors for the MOCVD of electroceramic oxides. Journal of Materials Chemistry 12(9), 2576-2590 Jones AC, Chalker PR (2003) Some recent developments in the chemical vapour deposition of electroceramic oxides. Journal of Physics D-Applied Physics 36(6), R80-R95 Kammler HK, Madler L, et al (2001) Flame synthesis of nanoparticles. Chemical Engineering Technology 24(6), 583-596... 

Jones CA. Molecular design of improved precursors for MOCVD of electroceramic oxides. J Mater Chem 2002 12 2576-90. 

Shi] Shin, H.S., Kwon, S.-J., A Suggestion on the Standard X-ray Powder Diffraction Pattern of Barium Ferrite , Powder Diffr., 7(4), 212-214 (1992) (Crys. Stracture, Experimental, 9) [1993Alc] Alcock, C.B., Thermodynamic and Transport Properties of Electroceramic Oxide Systems , J. Alloys Compd., 197,217-227 (1993) (Experimental, Phys. Prop., Review, Thermodyn., 28)... 

About 100,000 t of titanium dioxide aimuaHy are used as formulation components in the production of glass (qv), ceramics, electroceramics, catalysts, and in the production of mixed-metal oxide pigments. 

Precipitation of a hydrated titanium oxide by mixing aqueous solutions of titanium chloride with alkaU forms the precipitation seeds, which are used to initiate precipitation in the Mecklenburg (50) variant of the sulfate process for the production of pigmentary titanium dioxide. Hydrolysis of aqueous solutions of titanium chloride is also used for the preparation of high purity (>99.999%) titanium dioxide for electroceramic appHcations (see Ceramics). In addition, hydrated titanium dioxide is used as a pure starting material for the manufacture of other titanium compounds. 

Hertz JL and Tuller HL. Electrochemical characterization of thin films for a microsolid oxide fuel cell. J. Electroceram. 2004 13 663-668. 

N. Barsan and U. Weimar. Conduction model of metal oxide gas sensors , Journal of Electroceramics 7 (2001), 143-167. 

The publication of this book follows a Workshop on Polar Oxides - Properties, Characterizing and Imaging which was held in Capri, Italy, in June 2003. The chapters published here are up-dated and revised manuscripts of the contributions presented during the workshop. The workshop was organized in the framework of polecer - European Thematic Network on Polar Electroceramics which is part of the Growth European Community Program . 

Although dislocations have a significant effect on some of the important properties of electroceramics, especially those depending on matter transport, our understanding of them is, at best, qualitative. In contrast, there is a sound basis for understanding the effects of point defects and the relevant literature is extensive. It is for these reasons that the following discussion is confined to point defects and, because of the context, to those occurring in oxides. 

The PEM cell is the cleanest fuel cell since the fuel is hydrogen, the oxidant oxygen and the product water. Although it clearly falls outside the scope of a text focused on electroceramics there are good reasons for prefacing the present discussion with a brief outline of those elements of the science and technology basic to it and common to the ceramics-based fuel cells. Also, for an intelligent... 

The science of gas-sensors based on changes in electronic conductivity of a semiconducting ceramic is a complex matter depending upon a combination of surface chemistry and electron transport in mainly transition metal oxides. As is usual in exploiting electroceramics, the applications technology runs ahead of... 

Bae, J.M. and Steele, B.C.H., Properties of pyrochlore ruthenate cathodes for intermediate temperature solid oxide fuel cells. Journal of Electroceramics, 1999, 3, 37-46. 

Mixed-metal oxides constitute a significant proportion of electroceramics (e.g., ferroelectrics or superconductors). In addition, electrooptical ceramics such as Pb(LaZrTi)03(PLZT), PbNb2/3Mg1/303(PNM), and Bi4Ti3Ol2 received considerable attention. It may be pointed out that the low-temperature SG route appears to be more suitable for lead containing materials in view of the comparatively more volatile characteristic of lead oxide, which tends to disturb the desired stoichiometry of the multimetal oxide material involving lead, prepared by the MOCVD procedure. 

The valve metal oxide systems Zr02 and Hf02 and most of the typical electroceramic perovskite compounds such as BaTi03 and (Ba,Sr)Ti03 (BST) show an... 

L.E. and Granqvist, C.G. (2004) Gas sensing with perovskite-like oxides having ABOj and BOj structures. J. Electroceram., 13 (1-3), 721-6. 

Ceramics represent a vast outlet for bismuth compounds, particularly bismuth oxide. Small levels of inclusions have a remarkable impact on the performances of the materials used for electronics. Typical examples of electroceramics are those derived from sintered Bi203-3Sn02, Zn0 Bi203 or 2Bi203-3Ti02. Many of these ceramics can work as sensors for monitoring... 

Abstract Aluminates form in binary systems with alkali, alkaline earth or rare-earth oxides and share the high melting point and resistance to chemical attack of the pure A1203 end-member. This means that these ceramics have a variety of applications as cements, castable ceramics, bioceramics, and electroceramics. Calcium aluminate cements are used for example in specialist applications as diverse as lining sewers and as dental restoratives. 

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