Silver layers substituents

Many heterocyclic compounds have been made as colour couplers. The role of the heterocyclic residue can vary. It can actually be the colour former or an auxiliary substituent in the coupler to provide fine control over the desired features or it can be a leaving group in a two-equivalent coupler. One advantage of using two-equivalent couplers is that less silver is required which permits the coating of thinner layers which in turn gives sharper images. 

More recently, because of their high dielectric constants k > 20 000), lead-based relaxor ferroelectrics have been used as capacitor materials. These ceramics have the general chemical formula Pb(5i, 2)03) vvhere Bi is typically a low-valence cation and B2 is a high-valence cation. Compositions used in capacitor applications are frequently based on lead magnesium niobate, Pb(Mgi/3,Nb2/3)03, and lead zinc niobate, Pb(Zni/3,Nb2/3)03. Other substituents and modifiers are added so that dielectric layers of these materials can be densified at relatively low temperatures ( 900 °C). The low firing temperatures permit the use of relatively inexpensive cofired electrode materials, such as silver. Typically, tape casting is used in the preparation of the dielectric layers. 

---