American Chemical Society
cm0c02639_si_001.pdf (1.72 MB)

Local Structure and Order–Disorder Transitions in “Empty” Ferroelectric Tetragonal Tungsten Bronzes

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journal contribution
posted on 2020-09-18, 18:52 authored by Jason A. McNulty, David Pesquera, Jonathan Gardner, Andrei Rotaru, Helen Y. Playford, Matthew G. Tucker, Michael A. Carpenter, Finlay D. Morrison
The “empty” tetragonal tungsten bronze Ba4La0.671.33Nb10O30 displays both relaxor-like and normal dielectric anomalies as a function of temperature; the former is associated with loss of ferroelectricity and was proposed to originate from anion disordering [Chem. Mater. 2016, 28, 4616–4627]. Here we present total neutron scattering and pair distribution function (PDF) analysis, which shows an increase in the distribution of oxygen–oxygen distances at the relaxor transition and which supports the proposed anion disordering mechanism. The disordering process can be destabilized by reducing the average A-cation size (i.e., Nd-doping: Ba4(La1–xNdx)0.67Nb10O30); this introduces a more strongly propagating tilt system in line with the previously reported crystal-chemical framework model [Chem. Mater. 2015, 27, 3250–3261]. Mechanical loss data obtained using resonant ultrasound spectroscopy also indicate destabilization of the disordering process with increasing Nd-substitution.