High-temperature (high-$T)$ and high-electric-field (high-$E)$ effects on $\mathrm{Pb}\left[\right({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{2/3}{)}_{0.92}{\mathrm{Ti}}_{0.08}]{\mathrm{O}}_3$ were studied comprehensively by neutron diffraction in the ranges $300<~T<~550\mathrm{K}$ and $0<~E<~15\mathrm{k}\mathrm{V}/\mathrm{c}\mathrm{m}.$ We have focused on how phase transitions depend on preceding thermal and electrical sequences. In the field-cooling process $\left(E\Vert \right[001]>~0.5\mathrm{k}\mathrm{V}/\mathrm{c}\mathrm{m}),$ a successive cubic $\mathrm{}\left(C\right)\mathrm{}\to \mathrm{tetragonal}\mathrm{}\left(T\right)\mathrm{}\to$ monoclinic ${(M}_{\mathrm{C}})$ transition was observed. In the zero-field-cooling process, however, we have found that the system does not transform to the rhombohedral (R) phase as widely believed, but to an unidentified phase, which we call X. X gives a Bragg-peak profile similar to that expected for R, but the c axis is always slightly shorter than the a axis. As for field effects on the X phase, it transforms into the $M_{\mathrm{C}}$ phase via another monoclinic phase ${(M}_{\mathrm{A}})$ as expected from a previous paper [Noheda et al., Phys. Rev. B 65, 224101 (2002)]. At a higher electric field, we confirmed the field-induced $M_{\mathrm{C}}\to T$ transition, which shows a gradual c-axis jump contrary to a sharp c-axis jump observed by strain and x-ray diffraction measurements.

• Received 12 August 2002

DOI:https://doi.org/10.1103/PhysRevB.67.094111