Phase relations and lattice parameters in the system SrO-BaO-Nb2O5 focussing on SBN (SrxBa1-xNb2O6)

Journal article


Publication Details

Author(s): Göbbels M
Journal: Journal of Crystal Growth
Publisher: Elsevier
Publication year: 2004
Volume: 269
Journal issue: 2-4
Pages range: 324 - 332
ISSN: 0022-0248
Language: English


Abstract


In this paper we report the phase relations of the tetragonal tungsten bronze type strontium barium niobate (SrxBa1−xNb2O6) solid solution in the temperature range from 1200°C to 1450°C. The x-value depends on the synthesis temperature and reaches from 0.19 ⩽ x ⩽ 0.62 at 1200°C up to 0.18 ⩽ x ⩽ 0.84 at 1440°C. In addition lattice parameters of the stable phases at 1300°C depending on their chemical compositions are given.



Samples with different SrO:BaO:Nb2O5 ratios were sintered in vertical tube furnaces at suitable temperatures in air. The chemical composition of the quenched equilibrated phase associations were determined by EPMA. Lattice parameters of the resulting crystalline phases were derived from refinement of d-values from XRD patterns.



The phase field of SBN is strongly temperature dependent. The Ba-rich end-member of the solid solution contains 80 mol% Ba and 20 mol% Sr independently of the synthesis temperature. On the other hand the maximum Sr-content of the solid solution increases with temperature from 62 mol% Sr at 1200°C up to 84 mol% Sr at 1450°C. Also the Nb-content varies with temperature especially at synthesis temperatures below 1400°C. In particular at 1300°C the solid solution field of SBN extents to higher Nb-contents on the Ba-rich side leading to a Sr-free end-member of the solid solution. For this Ba-rich side of the solid solution series a substitutional formula Ba4Sr1−yNbyNb10O30+1.5y (0 ⩽ y ⩽ 1) can be given.



A new compound (Sr, Ba)5Nb8O25 in the SrO–BaO–Nb2O5 system has been found, exhibiting also a solid solution range. Chemical compositions of some previously described phases could be determined in more detail.



The lattice parameters of the tetragonal tungsten bronze cell (A12A24C4M12M28O30) depend on the chemical composition of the solid solution. In the Sr-rich region and at low Nb-contents the a-parameter shifts strongly while on the Ba-rich side and at high Nb-contents the variation is lower. The c-parameter increases with the Ba-content.


FAU Authors / FAU Editors

Göbbels, Matthias Prof. Dr.
Lehrstuhl für Mineralogie

Last updated on 2019-05-09 at 07:13