3. Modification of Complex Materials Using a Pressure-Assisted Heat Treatment

This chapter reports a physical method to modify materials structures using a pressure-assisted heat treatment (denoted PAHT). This method has attracted much attention to obtain of novel complex materials, mainly due to the use of the low-temperature and elevated gas (e.g., air) pressure. PAHT is performed into a hermetically closed chamber from specifically designed for this purpose. PAHT has been studied as a technique of thin film deposition and as an alternative treatment to modify the crystalline structure of novel complex materials. In the field of film deposition, PAHT uses crystalline powder of metal oxides to produce the films. Films obtained by PAHT are homogeneous and dense, with similar morphology to that found in the starting oxide particles. The fundamental mechanism of this PAHT is mainly based on the mass transfer from oxide particles to the substrate surface, which enables a strong thin film adhesion/interaction to the substrate surface. One of the greatest advantages of this methodology is the possibility of applying films on several kinds of substrates that include glasses, polymers, silicon, and so on. Hence, the PAHT causes structural modifications as well as creation of various types of defects in crystalline thin films and oxide powders. For example, ordered clusters can be disordered by the pressure action, leading to the significant changes in the physical and chemical properties of thin films and oxide powders. Furthermore, as will be shown in this chapter, the effect of air pressure on crystalline structures has opened up novel opportunities to the rational development of novel complex materials with tunable physical and chemical properties for a wide variety of technological applications of interest.