Confirmation of $M_B$-type monoclinic phase in $\mathrm{Pb}\left[\right({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}{)}_{0.71}{\mathrm{Ti}}_{0.29}]{\mathrm{O}}_3:$ A powder neutron diffraction study

Analysis of high-resolution powder neutron diffraction data for $\mathrm{Pb}\left[\right({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}{)}_{0.71}{\mathrm{Ti}}_{0.29}]{\mathrm{O}}_3$ is presented to show unambiguously that its structure is not rhombohedral but monoclinic of $M_B$ type. Presence of this phase in between the rhombohedral (R) and $M_C$ phase fields provides the missing link for the polarization rotation path $R-M_B-O\left(\mathrm{orthorhombic}\right)\mathrm{}-M_C-T$ (tetragonal) predicted by Vanderbilt and Cohen’s theory.