Tribochemische und thermische Umwandlungen von LnTa3O9 (Ln = Pr,Nd) – röntgenographische und elektronenmikroskopische Untersuchungen |
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Authors: | G Steinmann U Schaffrath R Gruehn |
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Abstract: | Tribochemical and Thermal Transitions of LnTa3O9 (Ln = Pr, Nd) — X-ray and Electron Microscopic Investigations Upon grinding crystals of M1? LnTa3O9 (Ln = Pr, Nd) 3] undergo a tribochemical phase transition. This leads to a new modifikation M2? LnTa3O9 with a significant higher density. We tried to find out more about the structure with high resolution electron microscopic investigations. According to electron diffraction and powder patterns the lattice parameters are (CuKα1, λ = 1,54051 Å): M2? PrTa3O9: a = 6.2545(7) Å, b = 7.6736(7) Å, c = 6.5316(8) Å, β = 93.93(9)°; M2? NdTa3O9: a = 6.2552(5) Å, b = 7.6598(7) Å, c = 6.5103(4) Å, β = 94.096(7)°; (Z = 2). Using the intensities of powder patterns two structure models were calculated (space group P21/m, P2/m; R < 20%, heavy metal positions only). A through focus series of high resolution images was in better agreement with the first model (space group P21/m). Both models show a remarkable similarity to the structure of M? CeTa3O9 4]. A thermal phase transition leads to M? PrTa3O9 and M? NdTa3O9 which are both isostructural to M? CeTa3O9. |
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