A-site size effect in a family of unfilled ferroelectric tetragonal tungsten bronzes : Ba4R0.67Nb10O30 (R = La, Nd, Sm, Gd, Dy and Y)
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The effect of A-cation size on the structural and electrical properties in a family of ferroelectric tetragonal tungsten bronzes (TTBs) Ba4R0.67□1.33Nb10O30 (R = La, Nd, Sm, Gd, Dy and Y; □ = vacancy) was investigated. In each case, the crystal structure, as determined from lab-based ambient powder X-ray diffraction (PXRD), is metrically tetragonal and can be refined in the P4bm space group. XRD data show an increased splitting of hk0 00l reflections with decreasing R cation size indicating an increasing tetragonal distortion (measured by tetragonality c/a). Dielectric data and ferroelectric measurements indicate that the ferroelectric Curie temperature, TC, increases with decreasing R size and so a direct correlation between TC and tetragonality/ionic radius of R is demonstrated. Rietveld refinements show that the large A2-site is fully occupied by Ba2+ and, in addition to the R cation size, the presence of vacancies at the A1-site (perovskite-like site) is also shown to strongly affect the stability of ferroelectricity in this structure type.
Gardner , J & Morrison , F 2014 , ' A-site size effect in a family of unfilled ferroelectric tetragonal tungsten bronzes : Ba4R0.67Nb10O30 (R = La, Nd, Sm, Gd, Dy and Y) ' Dalton Transactions , vol 43 , no. 30 , pp. 11687-11695 . DOI: 10.1039/c4dt00126e
This journal is © The Royal Society of Chemistry 2014. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence (http://creativecommons.org/licenses/by-nc/3.0/).
JG acknowledges the EPSRC and EaStCHEM for provision of a studentship via the doctoral training grant.
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