Non-ambient X-ray and neutron diffraction of novel relaxor ferroelectric xBi2(Zn2/3,Nb1/3)O3–(1 – x)BaTiO3

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%.