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Phase Transition in Ba 6−3 x (Sm 1− y La y ) 6+2 x Ti 18 O 54 ( x =0.5) Ceramics
Author(s) -
Qin Ni,
Liu Xiao Qiang,
Chen Xiang Ming
Publication year - 2006
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2006.01128.x
Subject(s) - analytical chemistry (journal) , materials science , phase transition , tungsten , rietveld refinement , phase (matter) , x ray crystallography , crystallography , atmospheric temperature range , differential thermal analysis , temperature coefficient , crystal structure , mineralogy , diffraction , chemistry , metallurgy , condensed matter physics , physics , thermodynamics , organic chemistry , chromatography , optics , composite material
The effect of La substitution for Sm was investigated in Ba 6−3 x (Sm 1− y La y ) 6+2 x Ti 18 O 54 ( x =0.5) ceramics in the entire range of y (0∼1.0). X‐ray diffraction (XRD) analysis indicated that the phase constitution of the present ceramics was sensitive to y , and an abnormal phase transition from the tungsten bronze‐type to a new Ba 16 Ce 32 Ti 64 O 192 ‐type solid solution was determined at y =0.6–0.9. The crystal structure of the new phase was refined by Rietveld refinement. The stability of the Ba 16 Ce 32 Ti 64 O 192 ‐type structure was discussed with the ordering of cations and the average radius of Ln 3+ . The Ba 16 Ce 32 Ti 64 O 192 ‐type phase was observed only in the sintered pellets but not in the loose powders in the investigated temperature range of 1200°–1350°C. A differential scanning calorimetric analysis (DSC) was performed for investigating the thermal effect of the phase transition. Discontinuous dielectric properties were observed corresponding to the phase transition. The Ba 16 Ce 32 Ti 64 O 192 ‐type phase has a much higher dielectric constant, a lower quality factor, and a larger positive temperature coefficient of resonant frequency at microwave frequencies in comparison with the tungsten bronze‐type phase. Besides, the dielectric loss of the Ba 16 Ce 32 Ti 64 O 192 ‐type phase is much lower (tan δ∼10 −4 ) at frequencies below 10 8 Hz, while the dielectric constant is insensitive to the frequency.