Pyrochlores. IX. Partially Oxidized Sn2Nb2O7 and Sn2Ta2O7: A Mössbauer Study of Sn(II,IV) Compounds

Knop, Osvald; Meads, R.E.; Parker, William G.

doi:10.1139/v73-154

Cited by 34 publications

(23 citation statements)

References 4 publications

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“…For instance, the Mössbauer intensity depends on the recoil-free fraction of Sn nuclei, and the fraction is temperature dependent. Stewart et al reported [18] the Mössbauer spectra at 4.2-290 K of Sn-Ta-O pyrochlore, which was iso-structure with the present Sn-Nb-O pyrochlore, and showed the smaller recoil-free fraction of Sn II than that of Sn IV at high temperature. Because the present spectrum was recorded at room temperature, the recoil-free fraction of Sn II was smaller than that of Sn IV as expected the results for Sn-Ta-O pyrochlore.…”

Section: Resultsmentioning

confidence: 65%

Characterization of novel cation-ordered compounds with fluorite and α-PbO2 related structures prepared by oxidation of Sn–Nb–O pyrochlore

Omata

Kita

Otsuka‐Yao‐Matsuo

et al. 2005

Journal of Physics and Chemistry of Solids

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Section: Resultsmentioning

confidence: 65%

Characterization of novel cation-ordered compounds with fluorite and α-PbO2 related structures prepared by oxidation of Sn–Nb–O pyrochlore

Omata

Kita

Otsuka‐Yao‐Matsuo

et al. 2005

Journal of Physics and Chemistry of Solids

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“…Since density measurements on the final, homogeneous prepamtions (samples ii) indicated incompletely occupied unit cells, the necessity of determining whether mixed valency states were present became apparent. Results of a Mossbauer 12'Sb investigation will be communicated in another paper of this series (33).…”

Section: Structure Refinementsmentioning

confidence: 97%

Pyrochlores. VIII. Studies of some 2–5 Pyrochlores and Related Compounds and Minerals

Brisse¹,

Stewart²,

Seidl³

et al. 1972

Can. J. Chem.

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The cubic pyrochlores Cd,Nb,O,, Cd2Ta,0,. S n 2 N b 2 0 j . S n z T a 2 0 7 . Cd,Sb20,, Ca2Sb,0,, M n 2 S b 2 0 i , PbzSb,O,. and related compounds were prepared and investigated by a number of methods. On heating above 700'. Ca,SbzO,(pyrochlorc) transformed to Ca,Sb,O,(weberitej, while Pb,Sb201(pyrochlore) changed to a rhombohedrally distorted P b 2 S b 2 0 j pyrochlore. Refinement of the crystal structures of Cd,Nb,O, and C d z T a 2 0 , from powderdiffractometer intensities yielded 0.434(2) and 0.434(3) respectively as the best estimates of .\. (O,). Specimens of natural bindheimite and stibiconite were also examined. Stibiconite from San Luis Potosi (Mexico) was shown. on the evidence of its Mossbauer "'Sb spectrum, to contain Sb(V) and Sb(II1) in the approximate ratio of 0.2.BaCd,CI,.5HI0 and BaCd2CI,.2H20 both give powder diffraction patterns of the pyrochlore type. The chlorine could be partially replaced by Br to give mixed crystals BaCd,CI,-,Brl,5H,0 almost up to z = 2.The crystal chemistry of 2-5 oxide pyrochlores and the relationship of the weberite to the pyrochlore phases are discussed. On discute d e la cristallochiniie des pyrochlores oxygknes de type 2-5 ainsi que de la relation entrc les phases pyrochlore et wdberite. Canadian Journal of Chemistry. 50, 3648 (1972) As a sequel to our previous investigations of oxide pyrochlores of compositions A;+B;+O, ( 3 -4 pyrochlores) and Ai+B:+O, ( 1 -5 pyrochlores) (IPS), some corresponding 2-5 pyrochlores have been studied. Minerals of this type (pyrochlore. niicrolite etc.) have been known for a long time. and the discovery of ferroelectricity in Cd2Nb20, (9) initiated a search for similar compounds with unusual dielectric properties. This search has proved disappointing in that it has uncovered but a minuscule number of new ferroelectrics of this structure type. It showed, however, that for some combinations of divalent and pentavalent cations the composition of the pyrochlore (P) phase is not limited to the ideal A,B,O, stoichiometry, while for other combinations oiz!v hypostoichiometric P phases can be prepared by conventional methods. The 2-5 pyrochlores are then best described by the general formula A , + = B 2 0 6 +,. The range of z is determined by the particular combination of A and B. and may include unity. The stability of the P structure can be correlated, for 3-4 pyrochlores, with the ionic size and radius ratio of the cations (10). A similar correlation is less satisfactorv for the 2--5 pyrochlores ( 1 1). Pentavalent cations of suitable size and chemistry are relatively few, and the absence, among divalent elements. of an extensive sequence of closely related ions, such as that formed by the trivalent lanthanons, makes each of the 2-5 P phases more unique. The Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.208.6.16 on 05/10/18For personal use only.

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“…However, the errors associated with the peak areas are sufficiently large that any small differences in the recoil-free fractions would not significantly alter the Sb"':Sbv ratio. It is of interest to note that in a recent investigation of non-stoichiometric pyrochlores resembling Sb60,, and containing simultaneously Sn2+ and Sn4+, the recoil-free fractions of these two valency species have been shown to differ by less than 10% (35).…”

Section: X-ray Diffractionmentioning

confidence: 99%

Pyrochlores. VII. The Oxides of Antimony: an X-Ray and Mössbauer Study

Stewart¹,

Knop²,

Ayasse³

et al. 1972

Can. J. Chem.

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Antimonic acid cannot be dehydrated by heating in air to give products of constant and reproducible weight without simultaneous reduction of some of the SbV to Sb"'. Neither anhydrous Sb20, nor the hydroxy oxide Sb3060H postulated by Dihlstrom and Westgren can be obtained by this method. Two well-defined products of the dehydration/decomposition are Sb204.,,,,, = Sb6013, which forms between 650 and 850", and p-Sb204. The latter, and not Sb203, results on heating Sb6013 to 935". Sb6OI3 has a cubic structure of the defect pyrochlore type, a, = 10.303(1) A, x(02) = 0.4304(14). Combined evidence from X-ray diffractometry, density determination, and Mossbauer spectroscopy leads to Sb3+SbS+,060,~, as the most probable structural formula.The Mossbauer parameters of P-Sb204 are closely similar to those reported for a-Sb204, but the isomer shifts (relative to InSb at 77 OK) for Sbv in antimonic acid and Sb6013 are significantly larger than those in a-and p-Sb,04.L'acide antimonique ne peut &tre deshydrate par chauffage a I'air pour donner des produits de poids con-

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Pyrochlores. IX. Partially Oxidized Sn₂Nb₂O₇ and Sn₂Ta₂O₇: A Mössbauer Study of Sn(II,IV) Compounds

Cited by 34 publications

References 4 publications

Characterization of novel cation-ordered compounds with fluorite and α-PbO2 related structures prepared by oxidation of Sn–Nb–O pyrochlore

Characterization of novel cation-ordered compounds with fluorite and α-PbO2 related structures prepared by oxidation of Sn–Nb–O pyrochlore

Pyrochlores. VIII. Studies of some 2–5 Pyrochlores and Related Compounds and Minerals

Pyrochlores. VII. The Oxides of Antimony: an X-Ray and Mössbauer Study

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