Quasi-amorphous materials

Quasi-amorphous films are the only known inorganic, non-crystalline, polar materials. The conditions under which they are formed and the origin of their polarity set these materials apart from other classes of inorganic materials. The unique feature of the quasi-amorphous phase is that its polarity is the result of flexoelectric-induced orientational ordering of local bonding units without any detectable spatial periodicity. However, unlike classical flexoelectricity - the reversible coupling of polarity and strain gradients - the strain gradient imposed on quasiamorphous films leads to permanent polarization, i.e. the polarization is retained even after the strain gradient has been eliminated. This mechanism permits compounds that do not have polar crystalline polymorphs, such as SrTiO₃ and BaZrO₃, to form polar, non-crystalline solids. In this chapter, we describe the essential features of quasiamorphous materials including preparation, structure, and chemical composition.