Abstract
The first determination of the phase diagram of the novel ferroelectric relaxor xBi(Zn2/3Nb1/3)O3-(1 - x)BaTiO3 (BZN-BT) has been achieved with a combination of high-resolution X-ray and neutron diffraction up to the miscibility limit near x(BZN) = 20.0% over a temperature range 20 < T < 400 K. The combined X-ray and neutron data show that the instability within the xBZN-(1-x)BT system reaches a maximum at x = 3.9% and is driven by B-site displacement and distortion of the oxygen octahedra in the polar phases. Composition-dependent effects include a narrow Amm2-dominated region focused at x = 3.9%, significant convergence of the lattice parameters in both P4mm and Amm2 phases, and sharp maxima in piezoelectric coefficient d 33 and maximum polarization P max. Lattice parameter dilation at x ≥ 4.0% was observed for both P4mm and Amm2 unit cells, alongside the first appearance of Pm 3 m at 295 K and the onset of significant dielectric relaxation. Low-temperature neutron diffraction indicated a weak or non-existent temperature dependence on the transition from ferroelectric at x = 3.9% to ferroelectric relaxor at x = 4.0%. Temperature-dependent phase transitions were eliminated near x = 3.0%, with the ferroelectric limit observed at x = 5.0% and a transition to a low-loss relaxor dielectric near x = 8.0%.
Highlights
The properties of relaxor ferroelectrics make them useful for a variety of applications including low-loss high-power dielectrics, electrocalorics and nonlinear optical materials (Cross, 1987; Bokov & Ye, 2006)
Relaxors are characterized by the presence of microscopic clusters a few unit cells in size, known as polar nanoregions (PNRs) (Cross, 1987; Bokov & Ye, 2006; Shvartsman et al, 2008; Shvartsman & Lupascu, 2012), which form on cooling through the Burns temperature (Td)
Dilute additions of BZN have a significant impact on the structure and dielectric properties of the BaTiO3 host
Summary
The properties of relaxor ferroelectrics make them useful for a variety of applications including low-loss high-power dielectrics, electrocalorics and nonlinear optical materials (Cross, 1987; Bokov & Ye, 2006). Recent studies of a lead-free BaTiO3-based analogue of PZN-PT, xBi(Zn2/3Nb1/3)O3–(1 À x)BaTiO3 (BZN-BT) (Ren et al, 2001; Zhou et al, 2018; Paterson et al, 2015), show interesting relaxor properties within the BaTiO3 host (Wu et al, 2016, 2017; Chen et al, 2015; Wang et al, 2014; Marshall et al, 2020) Previous studies of this system observed the presence of multiple polar phases at 295 K (Wu et al, 2017; Marshall et al, 2020), alongside maxima in dielectric constants and the piezoelectric coefficient d33 near x = 4.0%
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