Lead niobates

The Nb NMR spectra of a number of alkali and lead niobates have been acquired using MAS, DAS, MQMAS and two-dimensional nutation NMR to improve the resolution and determine values of the quadrupolar products Pq for these materials (Prasad et al. 2001). The 9.4 T Nb MAS NMR spectrum of LiNbOs spun at 25 kHz (Figure 10.16A) shows a lineshape dominated by the second-order quadrupolar interaction, with only marginal improvement in resolution at a field of 14.1 T. For most of the metal niobates, the second-order interaction is not removed by MAS alone, even at high magnetic fields and fast spinning speeds. The expected improvement in Nb resolution provided by DAS spectroscopy is offset by significant homonuclear... 

Detail studies on the reaction sequences in the Pb0-Fe203-Nb205-W03 and PMN systems [27-30] suggested that the perovskite phase was formed through a sequence of reactions involving several lead-niobate pyrochlores. From extensive differential thermal analysis and XRD analysis, Inada [30] proposed the following reactions in PMN ... 

The pure PbMgo.33Nbo.67O3 perovskite phase was crystallized at 1253 K from xerogel obtained by cogelation of Pb-acetate, Mg- and Nb-ethoxides in methoxyethanol [69]. Its purity was controlled by addition of excess Pb and Mg components that prevented formation of the lead niobate pyrochlore phase. 

Lead Niobate. Pb(Nb03)2 a ferroelectric compound having properties that make it useful in high-temperature transducers and in sensing devices. The Curie temperature is 570 = C. 

Geusic J.E., Kurts S.K., Van Uitert L.G., Wemple S.H. Electrooptic properties of some ABO3 perovskite in the paraelectric phase. Appl. Phys. Lett. 1964 4 141-143 Giess E.A., Scott B.A., Burns G., O kane D.F., Segmuller A. Alkali strontiirm-barium-lead niobate systems with a tungsten bronze structure Crystallographic properties and Curie points. J. Am. Ceram. Soc. 1969 52 276-281... 

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