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A synchrotron X-ray study of structural ordering in the microwave dielectric ceramic system: Ba(Ni1/3Nb2/3)O3–Ba(Zn1/3Nb2/3)O3.

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Title: A synchrotron X-ray study of structural ordering in the microwave dielectric ceramic system: Ba(Ni1/3Nb2/3)O3–Ba(Zn1/3Nb2/3)O3.
Authors: Cernik, R. J.1 r.cernik@manchester.ac.uk, Barwick, M.1, Azough, F.1, Freer, R.1
Source: Journal of Applied Crystallography. Aug2007, Vol. 40 Issue 4, p749-755. 7p. 4 Charts, 6 Graphs.
Subjects: Ceramics, Synchrotrons, Sintering, Statistical correlation, Spectrum analysis, Isostatic pressing
Abstract: Microwave dielectric ceramics in Ba(Ni1/3Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 (BNN–BZN) have been studied using high-resolution synchrotron powder diffraction. Two crystalline phases (cubic Pm m and trigonal P m1) have been found to coexist in both the BZN and BNN end members and mixed phases. A direct correlation between cooling rate (513 K h−1 to 275 K h−1) after sintering (annealing) and the growth of the trigonal ordered phase has been observed. The effect of annealing time (up to 72 h) at 1573 K has also been investigated for BNN ceramics and has been found to affect the growth of the ordered phase in a similar way to the variation of cooling rate. The degree of order in both BNN and BZN was found to increase with slow cooling and annealing from 28% to 38%, and from 10% to 31%, respectively. The degree of ordering in solid-solution samples prepared from a mixture of BZN and BNN also increased with slow cooling and annealing. In this case, the growth of the ordered phases were less well developed than those of the individual end members. Two surface-specific phases were found in the slowly cooled BZN sample, one of which was confirmed as Ba5Nb4O15 by wavelength dispersive spectroscopy (WDS) and Rietveld analysis; the other was found to be Ba8ZnNb6O24 by WDS. [ABSTRACT FROM AUTHOR]
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Abstract:Microwave dielectric ceramics in Ba(Ni1/3Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 (BNN–BZN) have been studied using high-resolution synchrotron powder diffraction. Two crystalline phases (cubic Pm m and trigonal P m1) have been found to coexist in both the BZN and BNN end members and mixed phases. A direct correlation between cooling rate (513 K h−1 to 275 K h−1) after sintering (annealing) and the growth of the trigonal ordered phase has been observed. The effect of annealing time (up to 72 h) at 1573 K has also been investigated for BNN ceramics and has been found to affect the growth of the ordered phase in a similar way to the variation of cooling rate. The degree of order in both BNN and BZN was found to increase with slow cooling and annealing from 28% to 38%, and from 10% to 31%, respectively. The degree of ordering in solid-solution samples prepared from a mixture of BZN and BNN also increased with slow cooling and annealing. In this case, the growth of the ordered phases were less well developed than those of the individual end members. Two surface-specific phases were found in the slowly cooled BZN sample, one of which was confirmed as Ba5Nb4O15 by wavelength dispersive spectroscopy (WDS) and Rietveld analysis; the other was found to be Ba8ZnNb6O24 by WDS. [ABSTRACT FROM AUTHOR]
ISSN:00218898
DOI:10.1107/S0021889807028051