NEXAFS and XPS and Structural, Electrical and Thermal Properties of Zn and Ni Codoped Bismuth Antimonate Pyrochlore

The crystal structure and physicochemical properties of a new Ni/Zn codoped bismuth antimonite pyrochlore, synthesized by the solid-phase reaction method, were investigated. The most optimal outcomes of Rietveld refinement for Bi2.7Zn0.46Ni0.70Sb2O10+Δ were achieved for the model of a disordered pyrochlore structure (sp.gr.Fd-3m:2, a = 10.46442(5) Å). Zinc and nickel atoms demonstrate an inhomogeneous mixed distribution across bismuth and antimony positions. The microstructure of the ceramic is characterized by low porosity, and is formed by faceted grains of 0.25–2 μm in diameter. The thermal expansion coefficient (TEC) increases monotonically from 7.14 × 10−6 °C−1 (30 °C) to 9.80 × 10−6 °C−1 (990 °C). At temperatures above 1080 °C, an atypical thermal dissociation of the pyrochlore occurs, resulting in the formation of bismuth-free compounds and two cubic phases that are stable when the sample is cooled. The Bi2.7Zn0.46Ni0.70Sb2O10+Δ compound is characterized by a band gap width of 2.4 eV. At temperatures below 200 °C, the sample exhibits predominantly capacitive impedance characteristics. The capacitance remains constant and independent of temperature and frequency up to a maximum of 150 °C. The high-frequency relative dielectric permittivity is low and equal to 26(3). The conduction activation energy in the sample is found to be 1.30(5) eV. Two polarization processes are detected in the sample. The electrical behavior of the sample has been modeled successfully by equivalent circuits within the temperature range of 200–450 °C. According to NEXAFS and XPS data, metal cations exhibit a conventional charge state, with an antimony oxidation state of +(5−δ).