Browsing by Author "R. Chakravarthy"

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Effect of powder synthesis procedure on calcium site occupancies in barium calcium titanate: A Rietveld analysis
(1993) P.S.R. Krishna; Dhananjai Pandey; V.S. Tiwari; R. Chakravarthy; B.A. Dasannacharya
(Ba,Ca)TiO3 samples with the ratio of (Ba+Ca) to Ti as unity but prepared by (i) a semiwet route involving (Ba,Ca)CO3 solid solution precursors and TiO2 and (ii) the conventional dry route involving BaCO3, CaCO3, and TiO2 powders, exhibit diffuse and BaTiO3-type sharp ferroelectric phase transitions, respectively. Rietveld analysis of neutron powder diffraction data from the two types of samples shows that, whereas in the samples prepared by the semiwet route, Ca2+ exclusively occupies the Ba2+ site, nearly half of the substituted Ca2+ occupies the Ti4+ site in the case of samples prepared by the dry route. We show that Ca replacement at the Ba site leads to diffuseness whereas Ca introduction at the Ti site leads to sharpening of the transition. To our knowledge, this is the first clear demonstration of the powder synthesis procedure affecting the substitutional sites in multicomponent ceramics and this, in turn, influencing their physical behavior drastically.
Neutron diffraction study of ferroelectric Ba0.88Ca0.12TiO3
(1991) V.S. Tiwari; Dhananjai Pandey; P.S.R. Krishna; R. Chakravarthy; B.A. Dasannacharya
Profile analysis of neutron diffraction data on Ba0.88Ca0.12TiO3 samples shows that Ca can enter either Ba site exclusively or both Ba and Ti sites depending on the method of preparation. Nature of structural phase transition has been examined in samples where Ca occupies Ba site only. © 1991.