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Erschienen in:
01.04.2015
Structure–property relationship in NaCa4B5O17 (B = Nb, Ta) perovskites
Erschienen in: Journal of Materials Science: Materials in Electronics | Ausgabe 4/2015
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Abstract
The crystal structure of NaCa4B5O17 (B = Nb, Ta) ceramics sintered at 1,200–1,350 °C was investigated. Analysis of X-ray diffraction (XRD) data revealed that both the NaCa4Nb5O17 and NaCa4Ta5O17 compounds crystallized into the monoclinic (P21/b) symmetry. The observed variation in the XRD peak intensities of NaCa4Nb5O17 with sintering temperature might be associated with the preferred orientation of grains rather than the change in crystal symmetry. Microstructural examination revealed a visible increase in grain size and change in grain morphology with increasing sintering temperature. The presence of the same active modes on the Raman spectra of samples sintered at 1,200–1,350 °C did not indicate any change in crystal symmetry with temperature. NaCa4Ta5O17 exhibited relative permittivity εr ~ 41, quality factor Q × f
o
~ 11,595 GHz and temperature coefficient of resonance frequency τf ~ −13.9 ppm/°C.