Ceramics, optical

The main categories of electrical/optical ceramics are as follows phosphors for TV, radar and oscilloscope screens voltage-dependent and thermally sensitive resistors dielectrics, including ferroelectrics piezoelectric materials, again including ferroelectrics pyroelectric ceramics electro-optic ceramics and magnetic ceramics. 

Care has to be taken in selecting materials for the die and punches. Metals are of little use above 1000 °C because they become ductile, and the die bulges under pressure so that the compact can only be extracted by destroying the die. However, zinc sulphide (an infrared-transparent material) has been hot pressed at 700 °C in stainless steel moulds. Special alloys, mostly based on molybdenum, can be used up to 1000 °C at pressures of about 80 MPa (5 ton in-2). Alumina, silicon carbide and silicon nitride can be used up to about 1400 °C at similar pressures and are widely applied in the production of transparent electro-optical ceramics based on lead lanthanum zirconate as discussed in Section 8.2.1. 

To appreciate properly how electro-optic ceramics function, it is first necessary to consider the nature of light and its interaction with dielectrics. 

Whether or not the dependence is expressed in terms of E or P is a matter of choice it seems customary in the literature relating to single crystals to use the r coefficient for the linear Pockels effect and g for the quadratic Kerr effect. In the case of electro-optic ceramics r and R are most commonly used. 

A complete description of the electro-optic effect for single crystals necessitates full account being taken of the tensorial character of the electro-optic coefficients. The complexity is reduced with increasing symmetry of the crystal structure when an increasing number of tensor components are zero and others are simply interrelated. The main interest here is confined to polycrystalline ceramics with a bias field applied, when the symmetry is high and equivalent to oomm (6 mm) and so the number of tensor components is a minimum. However, the approach to the description of their electro-optic properties is formally identical with that for the more complex lower-symmetry crystals where up to a maximum of 36 independent tensor components may be required to describe their electro-optic properties fully. The methods are illustrated below with reference to single-crystal BaTi03 and a polycrystalline electro-optic ceramic. 

Haertling, G.H. (1988) Electro-optic ceramics and devices. In Electronic Ceramics, L.M. Levinson (ed.), Marcel Dekker, New York, pp. 371-92. 

E. Zych, and C. Brecher, Temperature dependence of Ce-emission kinetics in YAG Ce optical ceramic. J. Alloys Compd. 300, 495-499 (2000). 

E. Zych, et al., Luminescence properties of ce-activated yag optical ceramic scintillator materials. J. Luminescence 75(3), 193-203 (1997). 

Some ceramics are transparent to light of specific frequencies. These optical ceramics are used as windows for infrared and ultraviolet sensors and in radar installations. However, optical ceramics are not as widely used as glass materials in applications in which visible light must be transmitted. An electro-optic ceramic such as lead lanthanum zirconate titanate is a material whose ability to transmit light is altered by an applied voltage. These electro-optic materials are used in color filters and protective goggles, as well as in memory-storage devices. 

We tried to obtain YAG optical ceramics doped with other d ions and to investigate properties of the samples. Ti ion can be a possible d dopant for YAG, and absorption and luminescence spectra of Ti were reported to resemble Ti3 spectra in sapphire It was found that Ti distribution in YAG depends strongly on crystal growth atmosphere, with appearance of precipitates in some cases. The situation can change in case of ceramics. So we decided at the beginning to investigate YAG Ti ceramics as well as YAG with less usual d dopant - Zr. ... 

Shoup, R. D., Gel-derived fused silica for large optics, Ceram. Bull., 70(9), 1505-1510 (1991). 

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