Re-examination of “Pb3TeO6”: Determination of its correct composition as Pb5TeO8

During systematic phase formation studies of lead oxotellurates(VI) under ambient pressure and at temperatures above 700 °C, we failed to reproduce the preparation of the previously reported ferroelectric compound with composition “Pb3TeO6”. Inconsistencies with respect to given crystallographic data and physical properties of this compound were clarified on basis of structure determination from single crystal X-ray data, revealing the true composition as Pb5TeO8 [P21/n, Z=4, a=7.4426(2), b=12.0107(3), c=10.6567(2) Å, β=91.040°, 7929 F2 data, 128 parameters, R[F2>2σ(F2)]=0.0318]. In the course of these investigations the crystal structure of the compound Pb6CdTeO10 [C2221, Z=4, a=9.1206(2), b=11.5674(3), c=11.3113(3) Å, 2924 F2 data, 85 parameters, R[F2>2σ(F2)]=0.0234] has been determined and the structural model of synthetic Pb2TeO5, previously described in the non-centrosymmetric space group Cc, has been revised [C2/c, Z=4, a=13.0853(6), b=5.7071(3), c=7.5225(3) Å, β=123.772(2)°, 1927 F2 data, 40 parameters, R[F2>2σ(F2)]=0.0335] and is compared with that of the mineral ottoite of the same composition.

The unprecedented [O4Pb10] unit in Pb5TeO8. Figure optionsDownload as PowerPoint slideHighlights
► Revision of the composition of previously reported “Pb3TeO6” as Pb5TeO8.
► Crystal structure determination of Pb2TeO5, Pb5TeO8, and Pb6CdTeO10.
► Correct relation between composition, crystal structure and physical properties of the compounds is reported.
► Revision of the space group of synthetic Pb2TeO5.