Elastic and anelastic relaxations accompanying relaxor ferroelectric behaviour of Ba6GaNb9O30 tetragonal tungsten bronze from resonant ultrasound spectroscopy
Schiemer, Jason A
Journal of Thermal Analysis and Calorimetry
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Rotaru, A., Schiemer, J. A., & Carpenter, M. (2016). Elastic and anelastic relaxations accompanying relaxor ferroelectric behaviour of Ba6GaNb9O30 tetragonal tungsten bronze from resonant ultrasound spectroscopy. Journal of Thermal Analysis and Calorimetry, 124 571-583. https://doi.org/10.1007/s10973-015-5202-z
Tetragonal tungsten bronze (TTB) structures offer some promise as lead-free ferroelectrics and have an advantage of great flexibility in terms of accessible composition ranges due to the number of crystallographic sites available for chemical substitution. The ferroic properties of interest are coupled with strain, which will be important in the context of stability, switching dynamics and thin film properties. Coupling of strain with the ferroelectric order parameter give rise to changes in elastic properties and these have been investigated for a ceramic sample of Ba6GaNb9O30 (BGNO) by resonant ultrasound spectroscopy (RUS). Room temperature values of the shear and bulk moduli for BGNO are rather higher than for TTB’s with related composition which are orthorhombic at room temperature, consistent with suppression of the ferroelectric transition. Instead, a broad, rounded minimum in the shear modulus measured at ~1 MHz is accompanied by a broad rounded maximum in acoustic loss near 115 K, and signifies relaxor freezing behaviour. Elastic softening with falling temperature from room temperature, ahead of the freezing interval, is attributed to the development of dynamical polar nanoregions (PNRs), while the non-linear stiffening below ~115 K is consistent with a spectrum of relaxation times for freezing of the PNR microstructure.
bulk modulus, ceramics, elastic properties, phase transitions, polar nanoregions (PNRs), relaxor dielectrics, resonant ultrasound spectroscopy (RUS), shear modulus, tetragonal tungsten bronzes (TTBs)
This work was supported by the strategic grant POSDRU/159/1.5/S/133255, Project ID 133255 (2014), co-financed by the European Social Fund within the Sectorial Operational Program Human Resources Development 2007 –2013. RUS facilities in Cambridge were established with funding from the Natural Environment Research Council (grants NE/B505738/1, NE/F017081/1) and from the Engineering and Physical Sciences Research Council (EP/I036079/1).
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External DOI: https://doi.org/10.1007/s10973-015-5202-z
This record's URL: https://www.repository.cam.ac.uk/handle/1810/253446