Naslov
Tailoring phase composition and microstructural features of Ba4Nb2O9 polymorphs via thermal decomposition route

Autori
Vrankić, Martina ; Popović, Jasminka ; Jurić Marijana

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of Abstracts of the 29th European Crystallographic Meeting (ECM29) / - , 2015, S384-s384

Skup
The 29th European Crystallographic Meeting

Mjesto i datum
Rovinj, Hrvatska, 23.08.2015. - 28.08.2015

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
phase composition; size and strain analysis; Rietveld refinement

Sažetak
Synthesis of nanoparticles with a controlled size has been found to be crucial for tailoring desired material properties since thermal, electric, optical, catalytic, and magnetic properties are strongly composition-, structure-, but also, size- and shape dependent.1, 2 It is well known that Ba4Nb2O9 exhibits mixed electronic, oxide ion, and proton conductivity, which makes it especially attractive in the field of fuel cells, steam electrolysers, and humidity sensors.3 Especially, the γ-Ba4Nb2O9 phase exhibits several orders higher conductivity than α Ba4Nb2O9 due to a faster protonic and oxide ionic transport.3 Up to now, the γ polymorph was metastable at room temperature (RT) and so could be isolated only by quenching the sample from high temperatures, because slow cooling led to a transformation to α phase.3 In the present study the mixed BaII−NbV containing oxides were prepared using {; ; Ba2(H2O)5[NbO(C2O4)3]HC2O4}; ; ·H2O as a single- molecular precursor. A systematic study of preparation conditions was carried out, namely, tuning the final structural and microstructural parameters by (i) the holding time (2, 1 and 0.5 h) at 1175 °C and (ii) the cooling rate (3, 7 and 12 °C min−1) from 1175 °C back to RT. Nanocrystalline products obtained by thermal decomposition of the precursor were investigated by X-ray powder diffraction at RT. Size and strain analysis were obtained in the course of the Rietveld refinement. Since all samples prepared by a cooling rate of 12 °C min −1 contained only the γ-Ba4Nb2O9 polymorph, it was evident that faster cooling prevented the γ → α phase transition, which resulted in the retention of the high-temperature γ- Ba4Nb2O9 phase at RT. Shortening of the time period for which γ-Ba4Nb2O9 containing samples were held at 1175 °C had no impact on their phase composition. All samples were found to be strain free. Crystallite sizes were ∼20 nm for γ-Ba4Nb2O9 prepared with a holding time of 2 h while it decreased to ∼5 nm with shortening of the holding time to 0.5 h. References: (1) Fernández-García, M. ; Martínez-Arias, A. ; Hanson, J. C. ; Rodriguez, J. A. Chem. Rev. 2004, 104, 4063−4104. (2) Burda, C. ; Chen, X. ; Narayanan, R. ; El- Sayed, M. A. Chem. Rev. 2005, 105, 1025−1102. (3) Ling, C. D. ; Avdeev, M. ; Kutteh, R. ; Kharton, V. V. ; Yaremchenko, A. A. ; Fialkova, S. ; Sharma, N. ; Macquart, R. B. ; Hoelzel, M. ; Gutmann, M. Chem. Mater. 2009, 21, 3853−3864.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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