of P4mm and P4bm tegragonal phases, which is in very good
agreement with the Rietveld refinement results for these
compositions.
The results confirm the validity of the MPB region proposed by
Takenaka et al., but partially disagree with the approach of Trelcat.
However, differently of the current proposals, in this work was
observed an additional tetragonal (P4bm) phase for BNBK compositions
into the MPB region.
4. Conclusions
BNBK100x ceramics with density higher than 95% were prepared
in this work. Rietveld refinements of the XRD patterns
indicated the BNBK82 sample has a single tetragonal symmetry
(P4mm) and the BNBK91 and BNBK93 samples, single rhombohedral
one (R3c). For BNBK88 and BNBK86 compositions was
observed the coexistence of the above two phases (R3c and P4mm)
with a not previously reported additional tetragonal P4bm phase.
Raman spectra deconvolution analysis confirmed the XRD results.
Estimated phase fraction from the Raman measurements are
in very good agreement with those estimated by Rietveld refinement,
evidencing the BNBK88 and BNBK86 compositions are
located in the MPB region of the BNBK system.
Acknowledgments
The authors would like to thank PVE/CAPES (processes
88881.062225/2014-01 and 88881.030500/2013-01) and grant
#2012/084577, grant #2013/001347 S~ao Paulo Research Foundation
(FAPESP), for the financial support.