Symmetry and cation displacements in hollandites

structure refinements of hollandite, cryptomelane and priderite.

J. E. Post, R. B. Von Dreele, P R Buseck

Research output: Contribution to journalArticle

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Abstract

Crystal structure determinations are reported for a) a hollandite, (Ba0.75Pb0.16Na0.10K0.04)(Mn,Fe,Al)8(O,OH)16, from Stuor Njuoskes, Sweden, with a 10.026(3), b 2.8782(7), c 9.729(3) A, beta 91.03(2)o, space group I2/m; b) a cryptomelane, (K0.94Na0.25Sr0.13Ba0.10)(Mn,Fe,-Al)8(O,OH)16, from Chindwara, India, with a 9.956(3), b 2.8705(9), c 9.706(4) A, beta 90.95(3) o, space group I2/m; c) a priderite, (K0.90Ba0.35)(Ti,Fe,Mg)8O16, from the West Kimberley area, Western Australia, with a 10.139(2), c 2.9664(9) A, space group I4/m. The symmetry of hollandite compounds depends on the ratio of the average ionic radius of the octahedral cations to that of the tunnel cations. Structures in which this ratio is >0.48 distort, reducing the tunnel volume, and thereby lowering the symmetry from tetragonal to monoclinic. The position occupied by a tunnel cation is determined primarily by the cation size. Relatively small cations, such as Ba2+ in priderite and Pb2+ in hollandite, displace from the special position, 2(a), to more stable sites that are at the sum of the ionic radii from the nearest O atoms. This study also indicates that the reduced form of Mn in hollandite and cryptomelane is Mn3+; the bond lengths suggest that the Mn3+ ion is more easily accommodated in the structures than the larger Mn2+.-J.E.C.

Original languageEnglish (US)
Pages (from-to)1056-1065
Number of pages10
JournalActa Crystallographica
VolumeB38
Issue numberPart 4
StatePublished - 1982

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Symmetry and cation displacements in hollandites : structure refinements of hollandite, cryptomelane and priderite. / Post, J. E.; Von Dreele, R. B.; Buseck, P R.

In: Acta Crystallographica, Vol. B38, No. Part 4, 1982, p. 1056-1065.

Research output: Contribution to journalArticle

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title = "Symmetry and cation displacements in hollandites: structure refinements of hollandite, cryptomelane and priderite.",
abstract = "Crystal structure determinations are reported for a) a hollandite, (Ba0.75Pb0.16Na0.10K0.04)(Mn,Fe,Al)8(O,OH)16, from Stuor Njuoskes, Sweden, with a 10.026(3), b 2.8782(7), c 9.729(3) A, beta 91.03(2)o, space group I2/m; b) a cryptomelane, (K0.94Na0.25Sr0.13Ba0.10)(Mn,Fe,-Al)8(O,OH)16, from Chindwara, India, with a 9.956(3), b 2.8705(9), c 9.706(4) A, beta 90.95(3) o, space group I2/m; c) a priderite, (K0.90Ba0.35)(Ti,Fe,Mg)8O16, from the West Kimberley area, Western Australia, with a 10.139(2), c 2.9664(9) A, space group I4/m. The symmetry of hollandite compounds depends on the ratio of the average ionic radius of the octahedral cations to that of the tunnel cations. Structures in which this ratio is >0.48 distort, reducing the tunnel volume, and thereby lowering the symmetry from tetragonal to monoclinic. The position occupied by a tunnel cation is determined primarily by the cation size. Relatively small cations, such as Ba2+ in priderite and Pb2+ in hollandite, displace from the special position, 2(a), to more stable sites that are at the sum of the ionic radii from the nearest O atoms. This study also indicates that the reduced form of Mn in hollandite and cryptomelane is Mn3+; the bond lengths suggest that the Mn3+ ion is more easily accommodated in the structures than the larger Mn2+.-J.E.C.",
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N2 - Crystal structure determinations are reported for a) a hollandite, (Ba0.75Pb0.16Na0.10K0.04)(Mn,Fe,Al)8(O,OH)16, from Stuor Njuoskes, Sweden, with a 10.026(3), b 2.8782(7), c 9.729(3) A, beta 91.03(2)o, space group I2/m; b) a cryptomelane, (K0.94Na0.25Sr0.13Ba0.10)(Mn,Fe,-Al)8(O,OH)16, from Chindwara, India, with a 9.956(3), b 2.8705(9), c 9.706(4) A, beta 90.95(3) o, space group I2/m; c) a priderite, (K0.90Ba0.35)(Ti,Fe,Mg)8O16, from the West Kimberley area, Western Australia, with a 10.139(2), c 2.9664(9) A, space group I4/m. The symmetry of hollandite compounds depends on the ratio of the average ionic radius of the octahedral cations to that of the tunnel cations. Structures in which this ratio is >0.48 distort, reducing the tunnel volume, and thereby lowering the symmetry from tetragonal to monoclinic. The position occupied by a tunnel cation is determined primarily by the cation size. Relatively small cations, such as Ba2+ in priderite and Pb2+ in hollandite, displace from the special position, 2(a), to more stable sites that are at the sum of the ionic radii from the nearest O atoms. This study also indicates that the reduced form of Mn in hollandite and cryptomelane is Mn3+; the bond lengths suggest that the Mn3+ ion is more easily accommodated in the structures than the larger Mn2+.-J.E.C.

AB - Crystal structure determinations are reported for a) a hollandite, (Ba0.75Pb0.16Na0.10K0.04)(Mn,Fe,Al)8(O,OH)16, from Stuor Njuoskes, Sweden, with a 10.026(3), b 2.8782(7), c 9.729(3) A, beta 91.03(2)o, space group I2/m; b) a cryptomelane, (K0.94Na0.25Sr0.13Ba0.10)(Mn,Fe,-Al)8(O,OH)16, from Chindwara, India, with a 9.956(3), b 2.8705(9), c 9.706(4) A, beta 90.95(3) o, space group I2/m; c) a priderite, (K0.90Ba0.35)(Ti,Fe,Mg)8O16, from the West Kimberley area, Western Australia, with a 10.139(2), c 2.9664(9) A, space group I4/m. The symmetry of hollandite compounds depends on the ratio of the average ionic radius of the octahedral cations to that of the tunnel cations. Structures in which this ratio is >0.48 distort, reducing the tunnel volume, and thereby lowering the symmetry from tetragonal to monoclinic. The position occupied by a tunnel cation is determined primarily by the cation size. Relatively small cations, such as Ba2+ in priderite and Pb2+ in hollandite, displace from the special position, 2(a), to more stable sites that are at the sum of the ionic radii from the nearest O atoms. This study also indicates that the reduced form of Mn in hollandite and cryptomelane is Mn3+; the bond lengths suggest that the Mn3+ ion is more easily accommodated in the structures than the larger Mn2+.-J.E.C.

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