A structure, conductivity and dielectric properties investigation of A3CoNb2O9 (A = Ca2+, Sr2+, Ba2+) triple perovskites

Abstract

The room temperature structures as well as the temperature-dependent conductivity and dielectric properties of the A 3CoNb 2O 9 (A=Ca 2+, Sr 2+ and Ba 2+) triple perovskites have been carefully investigated. A constrained modulation wave approach to Rietveld structure refinement is used to determine their room temperature crystal structures. Correlations between these crystal structures and their physical properties are found. All three compounds undergo insulator to semiconductor phase transitions as a function of increasing temperature. The hexagonal Ba 3CoNb 2O 9 compound acts as an insulator at room temperature, while the monoclinic Ca 3CoNb 2O 9 compound is already a semiconductor at room temperature. The measured dielectric frequency characteristics of the A=Ba compound are excellent. Measured temperature dependence of the electrical resistivity of the three A 3CoNb 2O 9, A=Ca, Sr and Ba, complex perovskite samples. Show more