Abstract

A new series of pyrochlore phases in the ternary oxide Tl–Sb–O have been prepared at 650 °C in air and characterised by XRD, FT-IR, EDX, XPS, and density measurements. The unit cell parameters were continuously decreased from 10.3073(1) Å for Tl/Sb = 1/4 to 10.28204(8) Å for Tl/Sb = 1/2 as the content of Tl³⁺ cations was increased. The Rietveld analysis shows that Tl⁺, Tl³⁺, Sb³⁺, and Sb⁵⁺ cations were positioned in the 32e, 16d, 96g, and 16c sites, respectively. The Tl³⁺ cations progressively incorporated into the 16d sites in the space group Fd3m, substituting for Sb³⁺ cations in the 96g sites. The FT-IR absorption band at around 570 cm⁻¹, corresponding to the Sb³⁺–O′ stretching vibrational mode, confirmed the existence of Sb³⁺ cations in the asymmetric 96g sites. These Tl–Sb–O phases are formulated with the composition (Tl⁺_{2/3 − 2δ})[Sb³⁺_1 − yTl³⁺_y]_2/3Sb⁵⁺₂O_{6.33 − δ} (δ ∼ 0.05) and exhibit quite unique structural features with three types of A/A′ cations in the 16d, 32e, and 96g sites.