Redefinition and crystal chemistry of samarskite-(Y), YFe 3+ Nb 2 O 8: cation-ordered niobate structurally related to layered double tungstates

Sergey N. Britvin, Igor V. Pekov, Maria G. Krzhizhanovskaya, Atali A. Agakhanov, Bernd Ternes, Willi Schüller, Nikita V. Chukanov

Результат исследований: Научные публикации в периодических изданияхстатьярецензирование

2 Цитирования (Scopus)

Аннотация

Samarskite-(Y), the mineral known for almost 180 years only in metamict (X-ray amorphous) state, was found as non-metamict crystals in sanidinites of the Laach Lake (Laacher See), Eifel volcanic region, Germany. The crystal structure has been solved for the first time and refined to R1 = 1.1% based on 838 observed [I > 2s(I)] independent reflections. Samarskite-(Y) is monoclinic, P2/ c, a 9.8020(8), b 5.6248(3), c 5.2073(4) A, beta 93.406(4)degrees, V 286.59(4) A3, Z = 2. The empirical formula (calculated on 8 O apfu) is Y 0.25 Ln 0.18 0.43 Th 0.37 U 4+ 0.13 Ca 0.03 0.96 Fe 3+ 0.73 Mn 2+ 0.18 0.91 Nb 1.85 Ti 0.06 Zr 0.06 Ta 0.03 W 0.02 2.02 O 8. Samarskite-(Y) from the type locality, the Blyumovskaya Pit, Ilmeny Mountains, South Urals, Russia, was studied for comparison; electron microprobe data showed the same species-defining constituents and stoichiometry: Y 0.34 Ln 0.20 0.54 U 4+ 0.42 Th 0.03 0.99 Fe 3+ 0.86 Mn 2+ 0.08 0.94 Nb 1.14 Ta 0.70 Ti 0.15 1.99 O 8. Samarskite-(Y) is the first example of cation-ordered niobate structurally related to layered double tungstates AMW2O8, the compounds used as luminophors and active media in solid-state lasers. The pseudo-layered framework of the mineral can be derived from that of wolframite via substitution of W for Nb, whereas each second -[FeO6] layer is replaced by -[YO8] one. The resulting sequence of layers can be expressed as -[AO8]-[BO6]-[MO6]-[BO6]-leading to the formula AMB2O8 in which A = Y, Ln, Th, -U4+, Ca; M = Fe3+, -Mn2+; and B = Nb, Ta, Ti. The end-member formula of samarskte-(Y) is -YFe3+ Nb2O8 (approved by the Commission on New Minerals, Nomenclature and Classification, International Mineralogical Association, memorandum 90-FH/ 18).

Язык оригиналаанглийский
Страницы (с-по)727-741
Число страниц15
ЖурналPhysics and Chemistry of Minerals
Том46
Номер выпуска7
DOI
СостояниеОпубликовано - июл 2019

Предметные области Scopus

  • Материаловедение (все)
  • Геохимия и петрология

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