ࡱ> @B?#`(+bjbj5G5G4,W-W-\,DdzzzzzzzFHHHHHH$h'l9_ zz_ _ lzz_ zzF_ FVJ@zX Pv0[ F0x7778z`  zzzllzzz_ _ _ _ $ RECRYSTALLIZATION OF HIGH-TEMPERATURE SAMARSKITE PHASE FROM METAMICT SAMARSKITE, BEINMYR, NORWAY 1N. Tomaai 1, V. Bermanec 1, M. Raji Linari 1Institute of Mineralogy and Petrography, University of Zagreb, Horvatovac bb, HR-10000 Zagreb, Croatia, e-mail:  HYPERLINK "mailto:ntomasic@geol.pmf.hr" ntomasic@geol.pmf.hr, 2 Pliva, HR-10000 Zagreb, Croatia INTRODUCTION Due to its very complex composition and natural occurrence in metamict state, samarskite crystal structure has not been resolved yet. Previous studies [1, 2] proposed two structural modifications for samarskite: a) low temperature samarskite, columbite-type structure (s.g. Pbcn), and b) high-temperature samarskite, wolframite-type structure (s.g. P2/c). In the metamict samarskite from Beinmyr, Norway, the relics of the proposed low temperature samarskite structure has been found [3]. The chemical composition of the sample also corresponds well to the assumed ABO4 stoichiometry [4, 5], yielding chemical formula Y0.27Ca0.24Fe0.21U0.14Ln0.1Nb0.76Ta0.26Ti0.06O4. Therefore, the sample was considered suitable for high-temperature annealing experiments in order to recrystallize the proposed high-temperature samarskite phase. EXPERIMENTAL Annealing experiments were performed in normal atmosphere at 400, 500, 650, 800 and 1000C for 24 hours in each case. The gradual recrystallization was monitored using X-ray powder diffraction (XRD). Additional annealing at temperatures around 1000C in Ar/H2 atmosphere were performed in order to obtain high-temperature samarskite phase as single phase [1]. XRD data were collected using Philips XPert Pro diffractometer with CuK( radiation at 45kV and 40 mA. Step size was 0.02 with a counting time of 20 s per step. The collected XRD data were evaluated by Rietveld refinement using PANalytical XPert Highscore Plus software. RESULTS AND DISCUSSION The X-ray diffraction patterns for the gradually recrystallized sample indicated pyrochlore as the first (re)crystallizing phase occurring at 400C. The samarskite high-temperature phase occurs at 800C coexisting with the pyrochlore phase. Both phases show increase in crystallinity if the annealing temperature is raised to 1000C, as inferred from peak width and intensity. Annealing experiments in slightly reducing atmosphere (Ar/H2) did not yield a single phase system containing only the high-temperature samarskite phase as suggested elsewhere [1,2,6]. The fact that the high-temperature annealing experiments, no matter they performed in reducing or oxidizing atmosphere, did not yield the samarskite as a single phase, seriously prevented structure refinement using proposed wolframite-type structure model with calculated unit cell parameters corresponding to P2/c symmetry. Since the cation distribution between the recrystallizing pyrochlore and high-temperature samarskite phase during annealing experiments is unknown, the unit cell parameters were refined using Le-Bail approach, which does not account for atomic positions. The refined unit cell parameters are: a=5.6264(7), b=9.918(2), c=5.2495(8), (=93.919(7) for samarskite, and a=10.2991(8) for the pyrochlore phase. The quality of Riteveld refinement is expressed in terms of weighted profile R value, Rwp, and goodness of fit, GoF, and equals 10.729 and 8.178 respectively. References: Sugitani Y., Suzuki Y., Nagashima K. // American Mineralogist, Vol (1984) ! 69, 377-379 Sugitani Y., Suzuki Y., Nagashima K. // American Mineralogist, Vol (1985) ! 70, 856-866 Tomaai24$ & ( *   / 0 1 E F H I i ʿʷʷʣm`XOXh@PH*mH sH h@PmH sH hAhm0JmH sH #jhAhmUmH sH jhmUmH sH hmmH sH hiihmH*mH sH hmh@Ph3|56hmh3|56h@P56H*hmhm56H* h@P56hmh3|56>*hmhm56>*H*h3|hmhMgK5 hB5 hu%5& ( j k l y z /ABYZ $a$gd$% $`a$gdsp$a$gdY^9$a$gdm$a$gd}ys(+i j l x y z   3 = a c          . 9 : B 俻سܪhFlhihuK hZXH*hZX h#xWH*h#xW hEH*hEhRhUhY^9 htg6htghtg6h4 htg6h:h$%hhtghmhwmhmmH sH hmmH sH 8 ;h)*+./wx AIXYZy%J]w~ÿ췳hh}&hEh&`h!mhB[hPQhuK hwhwhsphwhBh4_hK9h% ' jah% 'hFlhh hPH* h]DH*hPh]DhZXha5hhRhwmhm4z@GI  !Zel   ӿϻ߷ϳϳϳϳϳhUhlNNhah)lhz|h'>hah1+6h1+h$?whuKhBh] hl|H*hsphl|h}&h&`hhEE #&'(DGHIe  "2((((>)@)L)R)))))8*D*`*b*$+&+(+ȾȮȪȦȦȦȢț h3|hchBhrheh%hK%hK%H*hK%UhQ;hch$% hGJhhGJhGJ6H*hGJhGJ6hGJh)l jbhahahlNNhU9 "@))b*$+&+(+ $h^ha$gdc $ & Fa$gd$%$a$gd$% N., Gajovi A., Bermanec V., Raji Linari Maaa, Su D., Ntaflos T., Raade G. //19th General Meeting of International Mineralogical Association, Kobe 2006, 151 Komkov A.I. // Dokladii Akademie Nauk SSSR, Vol (1965) ! 160, 693-696 Warner J.K., Ewing R.C. // American Mineralogist, Vol (1993) ! 78, 419-424 Simmons W.B., Hanson S.L., Falster A.U. // The Canadian Mineralogist, Vol (2006) ! 44, 1119-1125 21h:pm/ =!n"n#n$n% DyK ntomasic@geol.pmf.hryK Pmailto:ntomasic@geol.pmf.hryX;H,]ą'c@@@ NormalCJ_HaJmH sH tH >A@> Zadani font odlomkaVi@V Obi na tablica4 l4a .k@. Bez popisa6U@6 m Hiperveza >*B*ph\,abcjklyz/ABYZ    i hZ[^0000000000000000000000000 0 0 0 0 0 000i (+  (+ (+0E\XFptGpNHpIptJp|SKp\PLpPMp#Np #OpQPp|RQpRRpRSp|_TplBUp]DGJMgKlNNPQR#xWB[4_&`{`Patg)lFlspr}ys$?wctw3|l|z|BuKamUY6iP]c e&Y!m.7E1+&lZXWm@PUO%:g@iiGEii4 \pp@pp(Unknownez Times New RomanArial Black CE5Symbol3& z Arial"qhBf@f2J J nn24UU2QHP)?C2aCrystal structure modelling of high-temperature samarskite phase: samarskite from Beinmyr, Norway Nenad Tomasicnenad   Oh+'0(4@P `l   dCrystal structure modelling of high-temperature samarskite phase: samarskite from Beinmyr, NorwayNenad TomasicNormalnenad50Microsoft Office Word@^(@lK/:@`/[J ՜.+,D՜.+,P hp  .PMF-MPZU bCrystal structure modelling of high-temperature samarskite phase: samarskite from Beinmyr, Norway Naslov 8@ _PID_HLINKSAp&\mailto:ntomasic@geol.pmf.hr  !"#$%&'()*+,-.012345689:;<=>ARoot Entry F@0[CData 1TableOWordDocument4,SummaryInformation(/DocumentSummaryInformation87CompObjs  F!Microsoft Office Wordov dokument MSWordDocWord.Document.89q