Ceramics, transparent

Ceramic processing typically consists of three main steps (i) synthesis or preparation of precursor powders, (ii) consolidation or packing of the powders into green bodies, and (iii) sintering [44]. Every step has a significant effect on the microstructure and optical performance of the final transparent ceramics. There are a number of parameters relevant to the quality of the powders, facility, and way of consolidation and techniques of sintering, which can be used to optimize the fabrication process as a whole. 

Precursor powders of ceramics can be prepared using solids, such as oxides, hydroxides, and carbonates, as starting materials [45-50]. In this case, it is called the solid-state reaction process. The precursor powders can also be synthesized by wet-chemical methods, such as chemical precipitation or co-precipitation [51-59], sol-gel [60, 61], gel combustion [62-65] and hydrothermal synthesis [66-69]. The 

It should be noted that the scattering is proportional to (r/X)4 and so, for example, if rjX is reduced from 10-1 to 10-2, the scattering decreases by a factor 

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The elements of flash goggles are a polarizer, a PLZT plate and a second polarizer arranged as shown in Fig. 8.15. The PLZT composition, 9.2/65/35, can be prepared by hot-pressing to a very pale yellow transparent ceramic with a grain size of about... 

Another interesting system is Pb/La/Zr/Ti/O with about 10 at% La. By a sintering process, a transparent ceramic is obtained. By applying voltage across such a ceramic, the plane of polarization is altered within microseconds. This feature is used in information display systems. 

Sintering studies on the Al203-rich side of stoichiometric spinel were carried out by Bailey and Russell [6]. Transparent ceramics were not the objective of this study, but several findings were noteworthy. Compositions from 71.67 wt % A1203 (stoichiometric spinel) to 93 wt % A1203 were... 

Although most ceramics are thermal and electrical insulators, some, such as cubic boron nitride, are good conductors of heat, and others, such as rhenium oxide, conduct electricity as well as metals. Indium tin oxide is a transparent ceramic that conducts electricity and is used to make liquid crystal calculator displays. Some ceramics are semiconductors, with conductivities that become enhanced as the temperature increases. For example, silicon carbide, SiC, is used as a semiconductor material in high temperature applications. 

S3/2— I15/2) of erbium ion have a laige emission section and are easy to achieve upconversion, so erbium ion is a good active ion as upconversion phosphors materials. The energy level transition( l]3/2— I15/2) can emit out 1.5 pm eye-safe laser radiation and the ion is also a well active ion for the eye-safe laser material. Gd203 powder with a cubic structure is a good host material for its excellent photics and thermal properties. It not only can be used as upconversion phosphors material but also can be used to prepare transparent ceramics as a host material. 

Microwave-transparent ceramics (MTC) has been used widely as output windows of traveling wave tube (TWT) in the field of microwave communication. Commonly, excellent mechanical property and thermal shock resistance are also required for MTC to release the heat caused by dielectric loss in time and prevent the thermal breakdown, besides low dielectric loss and high thermal conductivity. Recently, with the increment of output power and broadening of wave band, a higher mechanical property is desired in response to the miniaturization design of output windows. 

Figure 7 shows the transmittance of 3% La, 2% Yb co-doped yttria transparent ceramics. The highest transmittance reaches 75% at about 850 nm for 2mm thick sample. There are absorption peaks at about 950nm, which are the characteristic absorption peaks for Yb ion. 

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