In this chapter, various applications based on pyroelectricity of antiferroelectrics and relaxor ferroelectrics are presented from the material's point of view. While the pyroelectricity of the conventional antiferroelectric materials, such as PbZrO3, has been reported from the 1960s, the pyroelectricity of antiferroelectric HfxZr1-xO2 (x = 0.1-0.4) thin films was first reported in 2014. The antiferroelectric HfxZr1-xO2 (x = 0.1-0.4) thin films are believed to be highly promising for various applications, including electrostatic energy storage, electrocaloric cooling, pyroelectric energy harvesting, and infrared sensing. The theoretical background and basic operation principles of these energy-related applications will be briefly presented in the introduction. In this chapter, the material properties of only these new antiferroelectric thin films are dealt with because those of the conventional materials have been reported extensively elsewhere. In Sects. 17.2-17.5, the performance of HfxZr1-xO2 thin films in the aforementioned applications will be presented, and the performance of HfxZr1-xO2 films will also be compared with that of the conventional antiferroelectric and relaxor ferroelectric materials. In Sect. 17.6, the perspectives of antiferroelectric HfO2-based films in the aforementioned applications will be presented, with focus on the recently suggested future multifunctional monolithic device.
