کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9594200 | 1507518 | 2005 | 21 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
93Nb NMR chemical shift scale for niobia systems
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موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی تئوریک و عملی
پیش نمایش صفحه اول مقاله
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چکیده انگلیسی
93Nb solid-state NMR spectra of a series of inorganic niobates with Nb in different oxygen coordination environments were measured. For all studied compounds the chemical shielding and quadrupole tensor parameters were determined using conventional and ultrahigh field NMR facilities, ultrahigh speed MAS, DQ STMAS, solid-echo and computer modeling. It has been demonstrated that the 93Nb isotropic chemical shift is sensitive to the coordination number of Nb sites. For the first time the 93Nb NMR chemical shift scale for NbOx polyhedra in solid materials has been proposed: for four-coordinated Nb sites, the isotropic shifts occur from â650 to â950Â ppm; five-coordinated Nb sites have the isotropic shifts in the range of -900 to -980Â ppm; for six-coordinated Nb sites the isotropic shifts vary from â900 to â1360Â ppm; the shifts from â1200 to â1600Â ppm are typical for seven-coordinated Nb sites; for eight-coordinated Nb sites the shifts are higher than â1400Â ppm. The possible correlation between the value of the isotropic chemical shift and the ionic character of the NbOx-MOy polyhedra association has been suggested. The magnitude of the 93Nb quadrupole coupling constant depends on the local symmetry of Nb sites and may vary from hundreds of kHz to hundreds of MHz.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Solid State Nuclear Magnetic Resonance - Volume 28, Issues 2â4, September 2005, Pages 204-224
Journal: Solid State Nuclear Magnetic Resonance - Volume 28, Issues 2â4, September 2005, Pages 204-224
نویسندگان
Olga B. Lapina, Dzhalil F. Khabibulin, Konstantin V. Romanenko, Zhehong Gan, Mikhail G. Zuev, Vladimir N. Krasil'nikov, Vladimir E. Fedorov,