Preparation and crystal data of the New Pyrochlores Pb2[M1.5Te0.5]O6.5 (M = Ti, Zr, Sn, Hf)

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Abstract
From mixtures of PbO, MO2 (M = Ti, Zr, Hf), SnO, and TeO2, four new oxides Pb2[M1.5Te0.5]O6.5 have been obtained as yellow powders giving X‐ray diffraction patterns characteristic of cubic pyrochlores, S.G. Fd3m (No. 227), Z = 8, and a/Å values from 10.3529(1) (M = Ti) to 10.7406(1) (M = Zr). The best R factors, from 0.0465 (M = Ti) to 0.0242 (M = Hf), were obtained for Pb in 16(c) positions, M and Te (3:1) randomly distributed in 16(d), oxygen atoms in 48(f) and in a half of the 8(a) sites, and x values for the oxygen positional parameter (origin at center, 3m) from 0.436 (M = Ti) to 0.421 (M = Zr). For the compounds of Ti and Zr the angles of the coordination polyhedra around the metals are reported. For seven‐coordinated PbII the stereochemical influence of the nonbonded electron pair is shown. Apparent interatomic distances agree with those calculated.

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