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Influence of growth conditions on structural parameters of scheelite PbTO4 (T=Mo, W) crystals
Lead molybdates and tungstates with general chemical formula PbTO4 (PTO), where T is Mo (PMO) or W (PWO), were grown by the Czochralski method in an oxygen (PTO-A) or inert (PTO-N2) atmosphere from a stoichiometric mixture of corresponding oxides or mixture containing an excess of PbO (PMO-N2(Pb))....
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Published in: | Materials & design 2016-05, Vol.97, p.56-63 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Lead molybdates and tungstates with general chemical formula PbTO4 (PTO), where T is Mo (PMO) or W (PWO), were grown by the Czochralski method in an oxygen (PTO-A) or inert (PTO-N2) atmosphere from a stoichiometric mixture of corresponding oxides or mixture containing an excess of PbO (PMO-N2(Pb)). The crystals were investigated by X-ray and neutron single crystal and X-ray powder (Rietveld method) diffraction methods. For PWO-A and PWO-N2 crystals, the presence of additional reflections (50%) was revealed, indicating the symmetry reduction from space group I41/a to I4_ caused by kinetic (growth) order–disorder phase transition associated with an ordering/disordering of oxygen vacancies. In the structures of PMO samples, the vacancies are absent in the Mo and O sites (PMO-A and PMO-N2) and they are present in the Pb sites (except for PMO-N2(Pb)); the defect content being higher in the PMO-N2 crystal grown in an inert atmosphere. It is shown that the light yellow color of PTO crystals is due to the O and Pb vacancies, that may be accompanied by the transition Pb2+→Pb3+, and the gray-purple color of PMO-N2(Pb) is due to the transition Mo6+→Mo5+.
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•PbTO4 (T=Mo, W) crystal structures were refined by neutron and X-ray diffraction.•Symmetry reduction from space group I41/a to I4_ was first found for PbWO4 crystals.•The type and concentration of point defects were determined.•Coloration is caused by the Pb and O vacancy formation and Mo6+→Mo5+ transition. |
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ISSN: | 0264-1275 1873-4197 |
DOI: | 10.1016/j.matdes.2016.02.062 |