A new Pd3Pb2Te2 phase and its stable assemblages - Experimental approach
|Location||International Geological Congress,oslo 2008|
|Author||Vymazalovل, Anna; Drلbek, Milan; Laufek, Frantiڑek|
|Holding Date||04 October 2008|
The following phases related to the Pd-Pb-Te system have been described as minerals: native elements Pd, Pb and Te; PdTe - kotulskite, PdTe2 - merenskyite, Pd3-xTe - keithconnite, Pd9Te4- telluropalladinite, Pb3Pb zvyagintsevite, Pd3Pb2 plumbopalladinite, and PbTe - altaite. Nevertheless, only phase relations within the corresponding binary systems are known, the Pd-Pb-Te system was experimentally studied only in palladium rich corner (El-Boragy and Schubert, 1971). Therefore phase equilibria in the Pd-Pb-Te system was studied in the composition range from 0 to 60 at. % of Pd at 400°C and the results are presented in this contribution. The Kullerud`s evacuated silica-tube method was used for the purpose of this study. The undermentioned binary phases were confirmed to be stable in the system at 400°C: PdTe2, PdTe, Pd3Te2, PdPb2, PdPb, Pd13Pb9, Pd5Pb3 and PbTe. The Pd(Pb,Te) phase, analogous to the mineral kotulskite, forms an extensive solid solution(ss) and dissolves up to 30 at. % of Pb. Experimental results revealed the existence of a new Pd3Pb2Te2 ternary phase. The Pd3Pb2Te2 phase is orthorhombic, space group Pmmn, with the cell parameters: a = 8.599 Å, b = 5.9381 Å, c = 6.3173 Å. The measured d-spacing (and relative intensities) of Pd3Pb2Te2 are: 6.315(34), 3.157(33), 3.050(100), 2.968(24), 2.788(24), 2.546(63), 2.442(34), 2.279(42), 2.164(71), 2.150(30), 1.891(42), 1.729(21), 1.525(31), 1.326(20). The observed range in chemical composition is between Pd = 31.77-32.42 wt.%, Pb = 41.40-42.16 wt.% and Te = 25.68-26.30 wt.%. In reflected light the Pd3Pb2Te2 phase is pale pink with brownish tinge, and pleochroic from brownish to light pink, anisotropy is distinct to strong. The synthetic Pd3Pb2Te2 phase has a natural analogue that comes from Talnakh deposit, Noril’sk-Talnakh Ni-Cu camp, Russia. A proposal for a new mineral was submitted to IMA in December 2007. The following stable assemblages were observed in the Pd-Pb-Te system (composition range from 0 to 60 at. % of Pd) at 400°C: Pb - PbTe - PdPb2; PdPb2 - PbTe - PdPb; PdPb - PbTe - Pd13Pb9; Pd13Pb9 - PbTe - Pd(Pb,Te)ss; Pd(Pb,Te)ss - Pd3Pb2Te2 - PbTe; PbTe - Te - PdTe2; PbTe - PdTe2 - Pd(Pb,Te)ss; PbTe - Pd3Pb2Te2 - PdTe; Pd13Pb9 - Pd(Pb,Te)ss - Pd5Pb3; PdTe - Pd3Pb2Te2 - Pd(Pb,Te)ss. Besides a new ternary phase and known minerals of the marginal systems the following binary phases can be expected to be found in nature: Pd13Pb9, Pd3Pb5, PdPb, PdPb2, and Pd3Te2.