Transparent Polycrystalline Ceramics: An Overview

Transparent ceramics, a new class of advanced functional materials, find diverse applications in strategic and civilian sectors owing to its unique combination of mechanical and transmission properties. Technological advancements in ceramic powder synthesis, shaping and sintering have made it possible to tailor the microstructural, mechanical and optical property relationships in case of advanced transparent ceramic materials. Transparent ceramic materials are classified broadly as visible, mid wave and long wave infrared regions. The transparent ceramic systems, which are explored currently, include transparent alumina (as polycrystalline submicron alumina and single crystal sapphire (Al2O3)), aluminium oxynitride (AlON), spinel (MgAl2O4) and zinc sulphide (ZnS) ceramics. This review summarizes the status of the development of these ceramics and a case study on transparent zinc sulphide samples developed by chemical vapour deposition (CVD) followed by hot isostatic pressing (HIP). Physicochemical, thermal, optical, microstructure, hardness, flexural strength (sigma(f)), plane-strain fracture toughness (kappa(1c)) properties have been determined and correlated.