Nonferroelectric relaxor dielectric properties of pyrochlore phases

The family of materials with a pyrochlore structure exhibits a wide variety of technologically important physical properties, including ionic conductivity, photocatalytic activity, radiation resistance, and many others. However, the number of reliably established bulk ferroelectrics with a pyrochlore structure is extremely small (with the exception of cadmium niobate and related compounds). Instead, a large number of pyrochlores (primarily bismuth-containing) based on their temperature dependence of dielectric permittivity have a relaxor-like anomaly, which is not connected with the macroscopic ferroelectric phase transition. This chapter discusses the crystal-chemical and structural features of bismuth-containing pyrochlores that can cause the manifestation of nonferroelectric relaxor dielectric properties. In addition, a comparative analysis is given of the dielectric relaxation parameters of various compounds with the pyrochlore structure, discussed within the model of atomic hopping between crystallographically equivalent positions.