Temperature-dependent neutron diffraction study at the morphotropic phase boundary of $$(1-x)$$Bi(Fe$${}_{2/8}$$Ti$${}_{3/8}$$Mg$${}_{3/8}$$)O$${}_{3}$$–$$x$$PbTiO$${}_{3}$$†

The ferroelectric ceramic (0.675)Bi(Fe $${}_{2/8}$$ Ti $${}_{3/8}$$ Mg $${}_{3/8}$$ )O $${}_{3}$$ –(0.325)PbTiO $${}_{3}$$ is attractive because it contains low-lead content with a competitive piezoelectric coefficient, $${d}_{33}$$ of 100 pC/N. It also has a high-Curie temperature, ( $${T}_{\text{C}}$$ ) of 650 °C, although $${d}_{33}$$ reduces above 100 °C, being 0 pC/N at ( $${T}_{\text{d}}$$ ) = 525 °C. We clarified its temperature-dependent structure–property relationships on the average scale. Rietveld analysis against neutron powder diffraction, revealed three phase transitions: Cc + P4mm from RT to 600 °C; Cc + Pm $$\overline{3}$$ m from 610 to 680 °C; and Pm $$\overline{3}$$ m above 680 °C, over $${T}_{\text{C}}$$ . Dielectric permittivity increases at 610 °C, matching the symmetry change from P4mm to Pm $$\overline{3}$$ m. A broad diffuse phase transition is observed over a Curie range of 70 °C in the region Cc + Pm $$\overline{3}$$ m, potentially due to presence of microregions with local compositions different from the average composition over short length scales.