Pyrochlore-related phases in the lead oxide-tantalum oxide system

Stoichiometry, Defects, and Ordering in Lead Tantalum Oxides with Pyrochlore-Related Structures

“…4. This bright field image is (3)(4)(5)(6)(7)(8). chlore is not observed (8, 10, 11, 14-16), it can be supposed at least that the nonfaulted structure is a lead poor compound.…”

“…X-ray diffraction studies revealed that the powder consists actually It is well known that ordering of extended defects can generate a succession of crystallographically defined struc-of a mixing of two phases identified from JCPDS files tures, closely spaced in composition and closely related as the defect cubic pyrochlore phase Pb 1.5 Ta 2 O 6.5 (a ϭ in structure to each other and to the host structure (1, 1.056 nm) and the rhombohedral phase Pb 22 Ta 18 O 67 (in 2). For instance, such behavior has been experimentally hexagonal axes a ϭ 0.747 nm, c ϭ 4.813 nm) reported observed in the case of lead niobates with a pyrochlore by Scott (8). host structure.…”

“…A precise examination of the less developed faces of ray diffraction results, a rhombohedral phase similar to the crystals, e.g., the faces which are not perpendicular to one of those observed for lead niobates has been reported the ternary axis, show a lamellar structure (Fig. 1b); the but the existence of a solid solution has also been proposed obtained single crystals have a layered structure with a in the Pb 2.31 Ta 2 O 7.31 -Pb 2.44 Ta 2 O 7.44 composition range (8).…”

Low‐Temperature Synthesis of Lead Tantalate Pyrochlore Solid Solutions Pb1.5+x(Ta2−yPby)O7−δ (0.0 < x < 0.5; 0.0 < y < 0.6)

“…3 In Table I the observed and calculated diffraction patterns of the composition having a PbO/Ta 2 O 5 molar ratio of 3.5 with part of the Pb occupying the Ta sites are given. As shown in the table, the observed pattern matches reasonably well that of the calculated one, suggesting that the low-temperature cubic solid solution contains part of the Pb in the Ta sites leading to the formula Pb 1.5ϩx (Ta 2Ϫy Pb y )O 7Ϫ␦ (0.0 Ͻ x Ͻ 0.5; 0.0 Ͻ y Ͻ 0.6).…”

X-ray Structure Refinements and Strain Analysis of Substituted Cubic Lead Pyrochlores Pb2(M2−yPby)O7−δ(0.0<y<0.8; M=Nb or Ta)

“…The origin of the structure can be selected at the A, B, or the O site (1). Typically for lead niobates and tantalates, the assignment is that the A cations occupy the 16 (8,9). It is of interest to note that in all the above compositions the excess Pb is always found to be associated with the A-site.…”